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Question 1581Question →

A 68-year-old man presents to the emergency department complaining of sudden-onset, severe, "tearing" chest pain that radiates to between his shoulder blades. He has a history of poorly controlled hypertension and type 2 diabetes mellitus complicated by diabetic nephropathy. His current medications include amlodipine, lisinopril, and insulin glargine.

Blood pressure is 172/96 mmHg in the right arm and 148/88 mmHg in the left arm. Heart rate is 92/min, and respiratory rate is 18/min. Physical examination reveals a new early diastolic murmur heard best at the right sternal border.

Laboratory testing shows a serum creatinine of 3.4 mg/dL3.4 \text{ mg/dL} (baseline 3.1 mg/dL3.1 \text{ mg/dL}) and an estimated glomerular filtration rate of 17 mL/min/1.73m217 \text{ mL/min/1.73m}^2. An electrocardiogram shows left ventricular hypertrophy without acute ischemic changes. A portable chest radiograph demonstrates a widened mediastinum.

Which of the following is the most appropriate next step in imaging to confirm the diagnosis?

Show answer & explanation

Answer: Transesophageal echocardiography

Answer

Transesophageal echocardiography is the most appropriate next imaging study, as it provides definitive diagnosis without exposing the patient to contraindicated contrast agents.
The clinical presentation (sudden tearing chest pain radiating to the back, asymmetric arm blood pressures, new diastolic murmur, and widened mediastinum) is classic for an acute aortic dissection. To definitively establish the diagnosis, imaging must clearly delineate the aortic anatomy and locate the intimal flap. While computed tomography angiography is often the initial test of choice due to its speed and widespread availability, it requires iodinated contrast, which is absolutely contraindicated in this patient given his estimated glomerular filtration rate of 17 mL/min/1.73m². Magnetic resonance angiography is similarly contraindicated because gadolinium exposure in severe renal impairment carries a black-box warning for nephrogenic systemic fibrosis. Transesophageal echocardiography circumvents these issues; it does not require intravenous contrast, can be rapidly deployed at the bedside, and provides excellent visualization of the thoracic aorta (particularly the ascending segment and aortic valve), making it the most appropriate choice.

Step-by-Step Solution

1
Identify the primary suspected diagnosis based on the clinical presentation.
The patient's sudden tearing chest pain, asymmetric blood pressures, new early diastolic murmur (aortic regurgitation), and widened mediastinum are highly suggestive of an acute thoracic aortic dissection.
Establishing the pretest probability of the disease dictates the need for definitive confirmatory imaging.
2
Evaluate the patient's baseline physiological parameters and comorbidities for imaging contraindications.
The patient has severe renal impairment, with an estimated glomerular filtration rate (eGFR) of 17 mL/min/1.73m².
Renal function directly determines whether nephrotoxic contrast (iodine) or renally cleared contrast (gadolinium) can be safely administered.
3
Select the imaging modality that provides high diagnostic accuracy while avoiding contraindicated agents.
Transesophageal echocardiography is selected.
It offers excellent sensitivity and specificity for detecting intimal flaps in the thoracic aorta and can be performed rapidly at the bedside without requiring intravenous contrast.

Key Concept

In patients with suspected acute aortic dissection who have severe renal impairment or hemodynamic instability, transesophageal echocardiography is the imaging modality of choice to avoid the nephrotoxic effects of iodinated contrast and the risk of nephrogenic systemic fibrosis from gadolinium.
Estimated Time:1m 30s
Question 1582Question →

A 68-year-old man presents to the outpatient clinic with a 3-month history of episodic dizziness, ataxia, and diplopia. These episodes typically last for 5 to 10 minutes and resolve spontaneously. He recently noticed that these symptoms predictably occur when he vigorously uses his left arm to saw wood for his carpentry hobby. During these episodes, he also experiences cramping pain in his left forearm. His past medical history is significant for peripheral artery disease, hypertension, and a 40-pack-year smoking history. Current medications include aspirin, lisinopril, and atorvastatin. Vital signs show a blood pressure of 152/90 mmHg in the right arm and 110/68 mmHg in the left arm. Heart rate is 76/min and regular. Physical examination reveals a diminished left radial pulse compared to the right. Auscultation reveals a continuous bruit over the left supraclavicular area. Neurological examination is completely normal at rest. Based on the physical examination findings, which of the following is the most direct cause of this patient's neurological symptoms during exertion?

Show answer & explanation

Answer: Retrograde blood flow through the ipsilateral vertebral artery

Answer

The symptoms and physical examination findings are characteristic of subclavian steal syndrome, which is caused by retrograde blood flow through the ipsilateral vertebral artery.
This patient presents with classic physical examination findings of subclavian steal syndrome, characterized by a significant blood pressure discrepancy between the arms (typically a >15 mmHg systolic difference), a diminished pulse in the affected arm, and a supraclavicular bruit. This condition arises due to severe atherosclerotic stenosis or occlusion of the proximal subclavian artery, located proximal to the origin of the vertebral artery. When the patient exercises the affected arm, local peripheral vasodilation significantly lowers the vascular resistance in that extremity. Because the proximal subclavian artery is stenosed, forward blood flow is insufficient to meet the metabolic demand. Consequently, a pressure gradient is established that causes blood to flow up the intact contralateral vertebral artery to the basilar artery, and then travel in a retrograde direction down the ipsilateral vertebral artery to supply the arm. This 'steal' of blood from the vertebrobasilar system leads to transient posterior circulation neurological symptoms (such as dizziness, ataxia, and diplopia) exclusively during ipsilateral arm exertion.

Step-by-Step Solution

1
Analyze the physical examination findings.
Identify a significant systolic blood pressure discrepancy (>15 mmHg) between the arms, a diminished left radial pulse, and a left supraclavicular bruit.
These signs point to a severe stenosis or occlusion of the arterial supply to the left upper extremity.
2
Correlate the physical findings with the clinical presentation.
The patient experiences exertional left arm claudication paired with transient vertebrobasilar insufficiency (dizziness, ataxia, diplopia).
Simultaneous arm ischemia and posterior brain ischemia triggered by arm exercise is the hallmark of a vascular 'steal' phenomenon.
3
Deduce the precise anatomical lesion location.
The lesion must be a stenosis of the left subclavian artery proximal to the origin of the left vertebral artery.
Only a lesion proximal to the vertebral artery takeoff can cause the distal pressure to drop low enough to reverse the normal direction of vertebral blood flow.
4
Determine the pathophysiologic mechanism causing the neurological symptoms.
Left arm exertion causes vasodilation, creating a low-pressure sink that draws blood down the left vertebral artery in a retrograde fashion, stealing it from the basilar artery.
This hemodynamic shift temporarily deprives the brainstem and cerebellum of blood, producing the observed neurological deficits.

Key Concept

Subclavian Steal Syndrome Pathophysiology and Physical Findings
Question 1583Question →

A 42-year-old woman comes to the emergency department complaining of severe, constant right upper quadrant abdominal pain that began 18 hours ago after eating a large, high-fat meal. The pain radiates to her right scapula and is associated with nausea and two episodes of vomiting. She has no significant past medical history and takes no medications. Her temperature is 38.3∘C38.3^\circ\text{C} (100.9°F), heart rate is 102/min, blood pressure is 130/80 mmHg, and respiratory rate is 18/min. Physical examination reveals focal tenderness in the right upper quadrant with voluntary guarding, and inspiratory arrest occurs upon deep palpation of the right upper quadrant. Laboratory studies reveal a leukocyte count of 14,500/mm314,500/\text{mm}^3. Aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin, and lipase levels are all within normal limits. A comprehensive right upper quadrant abdominal ultrasound is performed. It demonstrates the presence of multiple gallstones within the gallbladder, but there is no gallbladder wall thickening, no pericholecystic fluid, and the common bile duct measures 4 mm in diameter. The sonographer notes that the sonographic Murphy sign is equivocal. Which of the following is the most appropriate next step in imaging for this patient?

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Answer: Cholescintigraphy

Answer

Cholescintigraphy is the most appropriate next step in imaging.
The correct answer is cholescintigraphy (hepatobiliary iminodiacetic acid or HIDA scan). This patient's clinical presentation (fever, right upper quadrant pain radiating to the scapula, focal tenderness, leukocytosis) is highly suggestive of acute cholecystitis. The initial imaging test of choice for suspected acute cholecystitis is a right upper quadrant abdominal ultrasound, which typically shows gallstones, gallbladder wall thickening (greater than 4 mm), pericholecystic fluid, and a positive sonographic Murphy sign. However, in this patient, the ultrasound is equivocal (gallstones are present, but there is no wall thickening or pericholecystic fluid, and an equivocal sonographic Murphy sign). When the clinical suspicion for acute cholecystitis remains high despite a non-diagnostic or equivocal initial ultrasound, the most appropriate next step in imaging is cholescintigraphy. During this scan, a radiotracer is injected intravenously, taken up by the liver, and excreted into the biliary tree. In acute cholecystitis, the cystic duct is obstructed by a gallstone, which prevents the radiotracer from entering the gallbladder. Therefore, non-visualization of the gallbladder on a HIDA scan is diagnostic for acute cholecystitis.

Step-by-Step Solution

1
Evaluate the clinical presentation.
The patient has symptoms and signs highly suspicious for acute cholecystitis (fever, right upper quadrant pain, leukocytosis, positive physical exam findings).
Establishing the pre-test probability guides the diagnostic imaging algorithm.
2
Analyze the results of the initial imaging study.
The initial right upper quadrant ultrasound shows gallstones but lacks definitive inflammatory signs (no wall thickening or pericholecystic fluid) and has an equivocal sonographic Murphy sign.
Ultrasound is the best initial test, but its results determine if further imaging is needed.
3
Determine the next best imaging step based on the equivocal initial results.
Select cholescintigraphy (HIDA scan) to definitively confirm or rule out cystic duct obstruction.
Cholescintigraphy has high sensitivity and specificity for acute cholecystitis and is the standard of care when ultrasound is non-diagnostic but clinical suspicion remains high.

Key Concept

When clinical suspicion for acute cholecystitis is high but initial abdominal ultrasound is equivocal, cholescintigraphy (HIDA scan) is the most appropriate next diagnostic imaging step.
Question 1584Question →

A 28-year-old man is brought to the emergency department by his roommate due to acute-onset agitation, confusion, and fever that began earlier today. The roommate reports that the patient had been feeling unwell with a "severe cold and dry cough" for the past three days. Past medical history is significant for major depressive disorder and allergic rhinitis. Surgical history includes an uncomplicated appendectomy at age 15. He drinks alcohol socially on weekends but denies illicit drug use. His prescribed daily medications include fluoxetine and a fluticasone nasal spray. Vital signs are temperature 38.8°C (101.8°F), blood pressure 158/96 mm Hg, heart rate 122/min, and respiratory rate 20/min. Physical examination reveals an agitated man with profuse diaphoresis and dilated pupils. Neurologic examination shows continuous horizontal eye movements (ocular clonus), bilateral lower extremity hyperreflexia, and inducible ankle clonus. Muscle tone is normal in the upper extremities but increased in the lower extremities. Which of the following specific historical elements is the most critical to elicit from the roommate to confirm the etiology of this patient's presentation?

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Answer: Recent use of an over-the-counter antitussive medication

Answer

Recent use of an over-the-counter antitussive medication
The correct answer identifies the need to ask about over-the-counter antitussive medications. This patient is exhibiting the classic clinical triad of Serotonin Syndrome: altered mental status, autonomic hyperactivity (diaphoresis, tachycardia, hyperthermia), and neuromuscular abnormalities (hyperreflexia, clonus). Since he is already taking fluoxetine (an SSRI), the addition of another serotonergic agent is the most likely trigger. The history of a recent 'dry cough' suggests he may have taken dextromethorphan, a common OTC cough suppressant that also inhibits serotonin reuptake and frequently precipitates Serotonin Syndrome when combined with SSRIs.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and physical exam findings.
The patient presents with altered mental status (agitation, confusion), autonomic instability (hyperthermia, tachycardia, hypertension, diaphoresis), and neuromuscular hyperactivity (ocular clonus, hyperreflexia, ankle clonus).
Identifying the specific triad of symptoms is required to diagnose the underlying toxidrome.
2
Correlate the toxidrome with the patient's known medication history.
The presentation is classic for Serotonin Syndrome. The patient is taking fluoxetine, a selective serotonin reuptake inhibitor (SSRI), which provides a baseline serotonergic load.
Serotonin Syndrome typically occurs when two or more serotonergic agents are combined, necessitating a search for the second agent.
3
Evaluate the recent history for potential interacting agents.
The patient has a 3-day history of a 'severe cold and dry cough'. Dextromethorphan is a widely available over-the-counter antitussive (cough suppressant) that acts as a serotonin reuptake inhibitor.
Eliciting a history of dextromethorphan use will confirm the etiology of the Serotonin Syndrome by identifying the interacting drug.

Key Concept

Patients taking serotonergic antidepressants (e.g., SSRIs) are at high risk for Serotonin Syndrome if they inadvertently consume over-the-counter medications with serotonergic properties, such as the antitussive dextromethorphan.
Question 1585Question →

Correlate the following specific cellular and molecular biopsy findings with the targeted pharmacologic agent most appropriate for exploiting that underlying neoplastic mechanism.

Click a left item, then click its matching right item

Items

Biopsy of a breast mass in a premenopausal patient reveals invasive carcinoma with marked ERBB2 gene amplification.
Bone marrow aspirate from a patient presenting with marked leukocytosis shows myeloid cells harboring the t(9;22)(q34;q11) translocation.
Tissue analysis of metastatic non-small cell lung cancer in a lifelong non-smoker demonstrates an EML4-ALK inversion.
Molecular profiling of recurrent high-grade serous ovarian carcinoma identifies a deleterious germline BRCA1 mutation.

Matches

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Answer

The correct matches pair the specific foundational molecular derangement identified in the biopsy with its corresponding targeted pharmacologic inhibitor.
Each correct pair accurately links a fundamental molecular derangement within a neoplastic cell to the pharmacologic agent specifically designed to inhibit or exploit that altered pathway.

Step-by-Step Solution

1
Analyze the molecular and genetic findings described for each neoplastic tissue sample.
Identified the specific pathogenic drivers: HER2 receptor amplification, BCR-ABL fusion kinase, ALK fusion kinase, and BRCA1-mediated homologous recombination deficiency.
Understanding the foundational mechanism driving the neoplastic process is essential to successfully selecting modern targeted therapies.
2
Correlate each identified molecular driver with its specific pharmacologic inhibitor.
Matched the molecular targets to trastuzumab, imatinib, crizotinib, and olaparib, respectively.
Targeted biologic therapies exploit highly specific cellular vulnerabilities, which differ significantly across varying cancer types.

Key Concept

Targeted oncologic therapies exploit specific molecular vulnerabilities characteristic of distinct neoplastic processes, such as oncogene addiction (e.g., HER2, BCR-ABL, ALK) or synthetic lethality (e.g., PARP inhibition in BRCA-mutated cells).
Question 1586Question →

An adult female patient is referred to the internal medicine clinic for evaluation of rapid, unexplained weight gain, severe proximal muscle weakness, and new-onset easy bruising over the past eight months. The patient is 39 years of age. Physical examination is notable for significant central adiposity, facial plethora, supraclavicular fat pads, and broad violaceous striae across her abdomen. Blood pressure is 158/96 mm Hg. Suspecting an endocrine etiology for her clinical presentation, the physician plans a step-wise diagnostic laboratory workup.

Arrange the following diagnostic laboratory investigations in the most appropriate sequential order for establishing the diagnosis and etiology of this patient's condition, from the initial diagnostic screening step to the final definitive localization step.

Drag items to arrange them in the correct order

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Answer

The correct sequence begins with confirming hypercortisolism via 24-hour urinary free cortisol, followed by establishing ACTH dependence by measuring plasma ACTH concentration, then attempting non-invasive source localization using a high-dose dexamethasone suppression test, and finally utilizing invasive localization with inferior petrosal sinus sampling if required.
The correct ordering strictly follows the standard endocrine guidelines for diagnosing Cushing syndrome. Proceeding out of this established sequence significantly increases the risk of diagnostic errors due to the physiological variability of these hormones and the high prevalence of incidental benign tumors on imaging.

Step-by-Step Solution

1
Confirm pathological hypercortisolism.
Order 24-hour urinary free cortisol measurement.
Before investigating the etiology, one must biochemically prove an excess of cortisol exists to prevent false positive diagnostic cascades.
2
Determine if the hypercortisolism is ACTH-dependent.
Order plasma ACTH concentration.
This step critically divides the diagnostic algorithm into ACTH-independent (adrenal tumors) and ACTH-dependent (pituitary or ectopic) pathways.
3
Differentiate the source of ACTH non-invasively.
Perform a high-dose dexamethasone suppression test.
Pituitary adenomas typically retain partial negative feedback mechanisms and will suppress cortisol production, whereas ectopic sources usually do not.
4
Definitively localize the source of ACTH invasively.
Perform inferior petrosal sinus sampling.
This is utilized when biochemical tests and imaging are equivocal, accurately measuring the central-to-peripheral ACTH gradient to confirm a pituitary source.

Key Concept

The diagnostic algorithm for Cushing syndrome requires strict sequential laboratory testing: first confirming hypercortisolism, second determining ACTH dependence, and finally localizing the exact source.
Question 1587Question →

A 32-year-old woman is evaluated in the outpatient clinic for a 6-month history of fatigue, intermittent abdominal bloating, and large, malodorous bowel movements. Over the same period, she has experienced a 4-kg (8.8-lb) unintentional weight loss. Her past medical history is notable for recurrent sinus infections during childhood, at which time she was diagnosed with selective IgA deficiency. She takes no medications and has no known drug allergies. Vital signs are within normal limits. Physical examination reveals pale conjunctivae and a highly pruritic, grouped vesicular eruption symmetrically distributed on her elbows and knees. Laboratory studies reveal a hemoglobin of 10.2 g/dL and a mean corpuscular volume (MCV) of 74 fL. Which of the following is the most appropriate next step in laboratory evaluation?

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Answer: Measurement of deamidated gliadin peptide IgG antibodies

Answer

Measurement of deamidated gliadin peptide IgG antibodies
The patient's presentation of malabsorption, iron deficiency anemia, and dermatitis herpetiformis is highly suspicious for celiac disease. While tissue transglutaminase (tTG) IgA is the standard initial screening test, this patient has a documented history of selective IgA deficiency. In such patients, IgA-based assays will be falsely negative. Therefore, testing must rely on IgG-based antibodies, such as deamidated gliadin peptide (DGP) IgG or tTG IgG, to accurately establish the diagnosis.

Step-by-Step Solution

1
Identify the underlying clinical syndrome based on the patient's presentation.
The combination of chronic diarrhea, weight loss, microcytic anemia, and dermatitis herpetiformis strongly indicates celiac disease.
Recognizing the disease is necessary to select the appropriate diagnostic pathway.
2
Determine the standard initial screening test for the suspected condition.
The standard initial serologic test for celiac disease is tissue transglutaminase (tTG) IgA antibody testing.
tTG-IgA is highly sensitive and specific in the general population.
3
Incorporate the patient's specific past medical history into the diagnostic plan.
The patient has a known history of selective IgA deficiency, meaning any IgA-based test will yield a false-negative result.
Comorbid conditions can invalidate standard diagnostic assays.
4
Select the appropriate alternative laboratory test.
An IgG-based assay, such as deamidated gliadin peptide (DGP) IgG or tTG IgG, must be ordered.
IgG-based testing retains high sensitivity and specificity for celiac disease in patients who cannot produce sufficient IgA.

Key Concept

Patients with suspected celiac disease and concurrent selective IgA deficiency must be screened using IgG-based serologic testing (e.g., deamidated gliadin peptide IgG or tTG IgG) rather than standard IgA-based assays to avoid false-negative results.
Estimated Time:1m 30s
Question 1588Question →

A 72-year-old woman is evaluated in the emergency department for severe right thigh pain and swelling that began spontaneously 2 days ago. She also reports easy bruising over her trunk and arms for the past 3 weeks. She has no prior history of abnormal bleeding, even during three uncomplicated vaginal deliveries and an open cholecystectomy at age 55. She takes no medications and has no family history of bleeding disorders. Physical examination reveals a massive, tense hematoma over the right anterior thigh and multiple large ecchymoses on the abdomen.

Laboratory studies are as follows:

Laboratory ParameterPatient ValueReference Range
Hemoglobin8.2 g/dL8.2 \text{ g/dL}12.0−15.5 g/dL12.0-15.5 \text{ g/dL}
Platelet count250,000/mm3250,000/\text{mm}^3150,000−400,000/mm3150,000-400,000/\text{mm}^3
Prothrombin time (PT)12.1 seconds12.1 \text{ seconds}11.0−15.0 seconds11.0-15.0 \text{ seconds}
Activated partial thromboplastin time (aPTT)86 seconds86 \text{ seconds}25−40 seconds25-40 \text{ seconds}
Thrombin time14 seconds14 \text{ seconds}<15 seconds< 15 \text{ seconds}

A 1:1 mixing study with normal pooled plasma is performed to further evaluate the prolonged aPTT:

ParameterPatient Value
Immediate aPTT37 seconds37 \text{ seconds}
Incubated aPTT (2 hours at 37∘C37^\circ\text{C})74 seconds74 \text{ seconds}

Which of the following is the most likely underlying mechanism for this patient's clinical and laboratory findings?

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Answer: Autoantibody directed against factor VIII

Answer

Autoantibody directed against factor VIII
The correct answer explains the pathophysiology of acquired hemophilia A. The patient has an isolated prolonged aPTT and severe, spontaneous, deep-tissue bleeding despite a negative bleeding history, which strongly points to an acquired inhibitor. The 1:1 mixing study is the critical differentiating test: factor deficiencies will correct immediately and remain corrected, while most inhibitors (like lupus anticoagulant) will fail to correct immediately. However, autoantibodies directed against factor VIII (acquired hemophilia A) are distinctively time- and temperature-dependent. They may initially appear to correct the aPTT immediately after mixing, but the aPTT will progressively prolong after a 1- to 2-hour incubation at 37∘C37^\circ\text{C} as the autoantibodies bind and neutralize the factor VIII in the normal pooled plasma.

Step-by-Step Solution

1
Analyze the basic coagulation panel.
The patient has an isolated prolonged aPTT with a normal PT, normal platelet count, and normal thrombin time.
An isolated prolonged aPTT narrows the differential to an intrinsic pathway issue (factor VIII, IX, XI, XII deficiency or an inhibitor like lupus anticoagulant or specific factor autoantibody).
2
Interpret the 1:1 mixing study results.
The immediate mix corrected the aPTT to normal (37 seconds), but the incubated mix became prolonged again (74 seconds).
Immediate correction suggests a factor deficiency, but subsequent prolongation after incubation at body temperature is the hallmark of a time- and temperature-dependent inhibitor, classic for factor VIII autoantibodies.
3
Synthesize laboratory findings with the clinical presentation.
An elderly patient with no prior bleeding history who suddenly develops life-threatening deep tissue bleeding (muscle hematoma) and a time-dependent factor VIII inhibitor.
This combination definitively establishes the diagnosis of acquired hemophilia A (autoantibody directed against factor VIII).

Key Concept

Interpretation of time-dependent inhibitors on mixing studies (Acquired Hemophilia A)
Question 1589Question →

A 42-year-old woman is evaluated in the outpatient clinic for medication-refractory hypertension. She is currently prescribed maximum tolerated doses of amlodipine, valsartan, and chlorthalidone. Despite reported medication adherence, her home blood pressure readings average 170/105 mm Hg. Over the past three months, she has developed progressive fatigue, polyuria, and painful muscle spasms in her calves. Her past medical history is notable for chronic dyspepsia, for which she prefers natural remedies over prescription antacids, and a laparoscopic cholecystectomy 5 years ago. She does not smoke or consume alcohol and works as a high school teacher. Vital signs show a blood pressure of 172/108 mm Hg and a heart rate of 78/min. Physical examination is notable for 4/5 motor strength in the proximal lower extremities; no abdominal bruits or striae are appreciated. Initial laboratory studies reveal a serum potassium of 2.6 mEq/L and a serum bicarbonate of 33 mEq/L. Subsequent hormonal evaluation demonstrates profoundly suppressed plasma renin activity and undetectable serum aldosterone levels. Which of the following elements of the patient's medical history is most critical to specifically elicit in order to establish the diagnosis?

Show answer & explanation

Answer: Detailed inventory of non-pharmacologic remedies and supplements for dyspepsia

Answer

The most critical historical element to elicit is a detailed inventory of non-pharmacologic remedies and supplements for dyspepsia, specifically to identify chronic licorice root ingestion.
The correct answer identifies the need to obtain a detailed supplement history. The patient's severe hypertension, hypokalemia, metabolic alkalosis, and suppressed renin/aldosterone levels characterize a syndrome of apparent mineralocorticoid excess. Her history of using natural remedies for dyspepsia strongly suggests chronic ingestion of licorice root (glycyrrhizin). Glycyrrhizin inhibits the enzyme 11-beta-hydroxysteroid dehydrogenase type 2 in the kidneys, preventing the conversion of active cortisol to inactive cortisone. The excess cortisol then inappropriately activates renal mineralocorticoid receptors, mimicking hyperaldosteronism but suppressing both endogenous renin and aldosterone. Thus, explicitly asking about her non-pharmacologic remedies is the critical diagnostic step.

Step-by-Step Solution

1
Analyze the patient's vital signs and laboratory findings in the context of her chief complaint.
The patient presents with severe, medication-refractory hypertension, profound hypokalemia, and metabolic alkalosis.
Identifying the clinical syndrome (mineralocorticoid excess) is the necessary first step before interpreting the hormonal workup.
2
Interpret the endocrine workup results to narrow the differential diagnosis.
Both plasma renin activity and serum aldosterone are profoundly suppressed.
Suppressed renin and aldosterone eliminate primary hyperaldosteronism (high aldosterone, low renin) and secondary hyperaldosteronism (high renin, high aldosterone), pointing toward an exogenous mineralocorticoid effect or rare genetic syndrome.
3
Correlate the pathophysiologic state with clues from the patient's background history.
The patient uses natural remedies for chronic dyspepsia. Licorice root (glycyrrhizin) is a common natural remedy for gastric distress that inhibits 11-beta-hydroxysteroid dehydrogenase type 2.
Connecting the biochemical pattern to a possible historical exposure allows the clinician to formulate a targeted diagnostic question.
4
Determine the most critical historical inquiry to establish the diagnosis.
Asking for a detailed inventory of supplements and remedies is essential.
Confirming exogenous glycyrrhizin ingestion definitively diagnoses her syndrome of apparent mineralocorticoid excess.

Key Concept

Patients presenting with treatment-resistant hypertension, hypokalemia, metabolic alkalosis, and suppressed renin/aldosterone should be carefully interviewed regarding the use of over-the-counter supplements, specifically licorice root, which causes a syndrome of apparent mineralocorticoid excess.
Question 1590Question →

Match each patient's specific occupational, environmental, or travel history to the most likely associated diagnosis based on their clinical presentation.

Click a left item, then click its matching right item

Items

A 45-year-old demolition worker renovating 19th-century homes who presents with severe abdominal colic, fatigue, and new-onset unilateral extensor weakness of the wrist.
A 52-year-old agricultural laborer who recently sprayed crops and now exhibits excessive salivation, miosis, bradycardia, and generalized muscle fasciculations.
A 38-year-old cave explorer returning from the Ohio River Valley with a subacute febrile respiratory illness, dry cough, and newly detected hepatosplenomegaly.
A 62-year-old retired shipyard worker presenting with progressive dyspnea on exertion, dry cough, and chest imaging revealing bilateral pleural plaques and lower lobe interstitial opacities.

Matches

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Answer

The correct matches correlate the demolition worker with Lead toxicity, the agricultural laborer with Organophosphate poisoning, the cave explorer with Histoplasmosis, and the shipyard worker with Asbestosis.
Each patient's distinct occupational, environmental, or travel history provides the critical diagnostic anchor that, when combined with their specific clinical presentation, leads to the correct diagnosis. Thorough medical history evaluation requires recognizing these classic historical triggers to avoid premature closure and misdiagnosis.

Step-by-Step Solution

1
Analyze the demolition worker's history.
Identified exposure to older building materials (lead paint), correlating with symptoms of abdominal pain and peripheral neuropathy (wrist drop).
To establish lead toxicity as the primary diagnosis over other heavy metal poisonings.
2
Analyze the agricultural laborer's history.
Identified recent pesticide exposure correlating with a classic cholinergic and nicotinic toxidrome.
To confirm organophosphate poisoning as the cause of the acute autonomic and neuromuscular symptoms.
3
Analyze the cave explorer's geographic and hobby history.
Identified endemic fungal exposure (bat guano in the Ohio River Valley), matching the pulmonary and disseminated reticuloendothelial findings.
To differentiate Histoplasmosis from other endemic mycoses or atypical pneumonias.
4
Analyze the retired shipyard worker's history.
Identified chronic occupational asbestos exposure, supported by pathognomonic imaging findings of pleural plaques and lower lobe fibrosis.
To distinguish asbestosis from other pneumoconioses like silicosis, which typically affects upper lobes.

Key Concept

Evaluating specific occupational, environmental, and travel histories is essential for diagnosing exposure-related toxicities, endemic infections, and pneumoconioses.

Alternative Method

When approaching matching questions based on history, first isolate the most unique geographic or occupational keyword (e.g., 'shipyard', 'spelunker') and link it to its classic pathology before verifying that the clinical symptoms align with that preliminary match.
Estimated Time:1m 30s
Question 1591Question →

A 6464-year-old man is evaluated in the emergency department for progressively worsening abdominal distension, shortness of breath, and bilateral lower extremity swelling over the past three weeks. His medical history includes long-standing alcohol use disorder, essential hypertension, and a myocardial infarction three years ago. His current medications are aspirin, metoprolol, and lisinopril. On physical examination, his temperature is 37.0∘C37.0^\circ\text{C} (98.6∘F98.6^\circ\text{F}), blood pressure is 130/80130/80 mmHg, heart rate is 88/min88/\text{min}, and respiratory rate is 18/min18/\text{min}. Jugular venous pulsation is visible 99 cm above the sternal angle. Abdominal examination reveals a positive fluid wave and shifting dullness. Bilateral 2+2+ pitting edema is present up to the knees.

Laboratory studies are as follows:

TestResultReference Range
Serum
Sodium136136 mEq/L136−145136-145 mEq/L
Creatinine1.11.1 mg/dL0.7−1.30.7-1.3 mg/dL
Albumin3.43.4 g/dL3.5−5.03.5-5.0 g/dL
Total protein6.56.5 g/dL6.0−7.86.0-7.8 g/dL
Total bilirubin1.81.8 mg/dL0.1−1.20.1-1.2 mg/dL
Ascitic Fluid
Albumin1.61.6 g/dL--
Total protein3.13.1 g/dL--
Cell count150/mm3150/\text{mm}^3--
Differential20%20\% segmented neutrophils, 80%80\% lymphocytes--

Based on the interpretation of these laboratory results, which of the following is the most likely etiology of this patient's abdominal fluid accumulation?

Show answer & explanation

Answer: Right ventricular failure

Answer

Right ventricular failure
The correct answer is right ventricular failure. Ascitic fluid analysis is critical for determining the etiology of a patient's ascites. The first diagnostic step is calculating the serum-ascites albumin gradient (SAAG), defined as the serum albumin concentration minus the ascitic fluid albumin concentration. In this patient, the SAAG is 3.4−1.6=1.83.4 - 1.6 = 1.8 g/dL. A SAAG ≥1.1\ge 1.1 g/dL indicates that the ascites is caused by portal hypertension. The second step is assessing the ascitic fluid total protein to narrow the differential. Post-hepatic causes of portal hypertension (e.g., right ventricular failure, constrictive pericarditis, Budd-Chiari syndrome) cause hepatic sinusoidal congestion and the leakage of protein-rich hepatic lymph into the peritoneum, resulting in an ascitic fluid total protein ≥2.5\ge 2.5 g/dL. In contrast, intrahepatic causes (e.g., cirrhosis) lead to capillarization of the sinusoids and yield a low-protein ascites (<2.5< 2.5 g/dL). This patient's high SAAG and high ascitic protein profile firmly point to a post-hepatic etiology. This is further corroborated by his physical examination showing elevated jugular venous pulsation (99 cm) and a history of myocardial infarction, confirming cardiac ascites secondary to right ventricular failure.

Step-by-Step Solution

1
Calculate the serum-ascites albumin gradient (SAAG).
The SAAG is 3.4−1.6=1.83.4 - 1.6 = 1.8 g/dL, which is ≥1.1\ge 1.1 g/dL.
To determine if the ascites is driven by portal hypertension or a non-portal hypertensive process.
2
Evaluate the ascitic fluid total protein level.
The ascitic total protein is 3.13.1 g/dL, which is ≥2.5\ge 2.5 g/dL.
To differentiate between intrahepatic (low protein) and post-hepatic (high protein) causes of portal hypertension.
3
Correlate the laboratory interpretation with the patient's clinical findings.
The combination of high SAAG and high ascitic protein aligns with the patient's elevated jugular venous pressure and history of myocardial infarction.
To confirm the specific post-hepatic etiology (cardiac ascites due to right ventricular failure) over other potential causes.

Key Concept

Interpretation of ascitic fluid analysis requires calculating the serum-ascites albumin gradient (SAAG) to diagnose portal hypertension (≥1.1\ge 1.1 g/dL) and evaluating ascitic total protein to differentiate intrahepatic (<2.5< 2.5 g/dL) from post-hepatic (≥2.5\ge 2.5 g/dL) etiologies.
Estimated Time:1m 30s
Question 1592Question →

An obstetrician is asked to evaluate a patient in the emergency department. The patient, pregnant with twins at 1010 weeks gestation, has been experiencing intractable vomiting, leading to severe dehydration and a weight loss of 4 kg4\text{ kg} (8.8 lbs8.8\text{ lbs}) over the last two weeks. During the evaluation, the physician notes a resting heart rate of 115/min115/\text{min} and a fine resting tremor. The patient mentions she feels constantly hot despite the room being air-conditioned. Examination of the neck reveals no thyromegaly or cervical lymphadenopathy, and eye examination is unremarkable.

Initial laboratory investigations show a human chorionic gonadotropin (hCG) level of 245,000 mIU/mL245,000\text{ mIU/mL}, a suppressed thyroid-stimulating hormone (TSH) level of 0.05 \muU/mL0.05\text{ \mu U/mL}, and an elevated free thyroxine (free T4) level of 2.5 ng/dL2.5\text{ ng/dL}.

Which of the following best explains the cellular mechanism underlying this patient's abnormal thyroid laboratory profile?

Show answer & explanation

Answer: Activation of the G-protein-coupled thyrotropin receptor by a structurally homologous placental glycoprotein

Answer

Activation of the G-protein-coupled thyrotropin receptor by a structurally homologous placental glycoprotein
The correct answer accurately describes the mechanism of gestational transient thyrotoxicosis. Human chorionic gonadotropin (hCG) is a glycoprotein that shares an identical alpha subunit with thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH). In conditions where hCG levels are exceptionally high, such as hyperemesis gravidarum, multiple gestations, or molar pregnancies, the beta subunit of hCG exhibits enough structural homology to directly bind and stimulate the G-protein-coupled TSH receptor on thyroid follicular cells. This stimulation leads to increased production of thyroid hormones (elevated free T4), which exerts negative feedback on the pituitary, resulting in a suppressed TSH level.

Step-by-Step Solution

1
Analyze the clinical presentation and laboratory findings.
The patient has clinical thyrotoxicosis (tachycardia, tremor, heat intolerance) with laboratory confirmation (suppressed TSH, elevated free T4) in the setting of hyperemesis gravidarum and twin gestation.
Establishing the functional thyroid status and correlating it with the specific pregnancy complications is required to identify the etiology.
2
Identify the hormonal abnormalities associated with the patient's specific pregnancy state.
Twin gestation and hyperemesis gravidarum are both characterized by exceptionally high levels of human chorionic gonadotropin (hCG), which is confirmed by the lab value of 245,000 mIU/mL245,000\text{ mIU/mL}.
Connecting the obstetric findings to the endocrine profile narrows down the pathophysiological mechanism.
3
Determine the biochemical relationship between hCG and thyroid function.
hCG shares an identical alpha subunit with TSH. High levels of hCG cross-react with the TSH receptor, stimulating the thyroid gland to produce excess T4 and subsequently suppressing endogenous TSH.
This structural homology perfectly explains the transient thyrotoxicosis without requiring an underlying autoimmune or destructive thyroid pathology.

Key Concept

Gestational transient thyrotoxicosis occurs because hCG shares an identical alpha subunit with TSH; at very high concentrations (e.g., hyperemesis gravidarum, multiple gestation), hCG directly stimulates the TSH receptor.
Question 1593Question →

Match each clinical laboratory profile with the most likely underlying diagnostic entity.

Click a left item, then click its matching right item

Items

A 4141-year-old woman presents with palpitations. Labs: TSH\text{TSH} 0.02 \muU/mL0.02 \text{ \mu U/mL}, Free T4\text{Free T4} 0.6 ng/dL0.6 \text{ ng/dL} (Low), Free T3\text{Free T3} 6.4 pg/mL6.4 \text{ pg/mL} (High), Thyroglobulin\text{Thyroglobulin} <0.1 ng/mL<0.1 \text{ ng/mL} (Low), 2424-hour RAIU 1%1\%.
A 3535-year-old man presents with diffuse goiter and bitemporal hemianopsia. Labs: TSH\text{TSH} 7.8 \muU/mL7.8 \text{ \mu U/mL} (High), Free T4\text{Free T4} 2.9 ng/dL2.9 \text{ ng/dL} (High), Free T3\text{Free T3} 5.6 pg/mL5.6 \text{ pg/mL} (High). SHBG is elevated. Pituitary α\alpha-subunit to TSH\text{TSH} molar ratio is 2.52.5 (Ref: <1.0<1.0).
An asymptomatic 2929-year-old woman is evaluated during a routine physical. Labs: TSH\text{TSH} 5.5 \muU/mL5.5 \text{ \mu U/mL} (High), Free T4\text{Free T4} 2.6 ng/dL2.6 \text{ ng/dL} (High), Free T3\text{Free T3} 5.2 pg/mL5.2 \text{ pg/mL} (High). SHBG is normal. Pituitary α\alpha-subunit to TSH\text{TSH} molar ratio is 0.40.4 (Ref: <1.0<1.0).
A 6868-year-old man in the intensive care unit with severe sepsis. Labs: TSH\text{TSH} 0.6 \muU/mL0.6 \text{ \mu U/mL} (Normal), Free T4\text{Free T4} 1.1 ng/dL1.1 \text{ ng/dL} (Normal), Free T3\text{Free T3} 1.2 pg/mL1.2 \text{ pg/mL} (Low), Reverse T3\text{Reverse T3} 550 pg/mL550 \text{ pg/mL} (High).

Matches

Show answer & explanation

Answer

The correct matches are: Profile 1 maps to Exogenous liothyronine administration; Profile 2 maps to TSH-secreting pituitary adenoma; Profile 3 maps to Resistance to thyroid hormone; Profile 4 maps to Non-thyroidal illness syndrome.
The profiles accurately reflect the pathophysiological laboratory findings unique to each disease state. Distinguishing factitious T3 toxicosis requires noting the low T4 and Thyroglobulin. Distinguishing TSH-oma from RTH requires analyzing SHBG and alpha-subunit. Distinguishing non-thyroidal illness requires noting the elevated Reverse T3.

Step-by-Step Solution

1
Analyze the first clinical profile showing isolated T3 elevation with suppressed TSH and low T4.
Identified as exogenous liothyronine administration.
Exogenous T3 administration raises Free T3, which suppresses central TSH secretion. The lack of TSH stimulation leads to ceased endogenous thyroid production, marked by low Free T4 and undetectable thyroglobulin.
2
Compare profiles two and three, which both show central hyperthyroidism patterns (High TSH, High T4, High T3).
Profile 2 is a TSH-secreting adenoma; Profile 3 is Resistance to Thyroid Hormone (RTH).
TSH-omas (Profile 2) cause true thyrotoxicosis (driving up hepatic SHBG production) and concurrently overproduce pituitary alpha-subunits. RTH (Profile 3) is a receptor defect where tissues do not respond normally to T4/T3, resulting in normal SHBG (no peripheral thyrotoxicosis) and a normal alpha-subunit ratio.
3
Examine the fourth profile showing an ICU patient with low T3 but high Reverse T3.
Identified as non-thyroidal illness syndrome (euthyroid sick syndrome).
During critical illness, 5'-deiodinase activity decreases, reducing the conversion of T4 to T3 and shifting conversion toward the inactive metabolite Reverse T3.

Key Concept

Advanced interpretation of thyroid function tests requires integrating secondary biomarkers (Thyroglobulin, SHBG, Alpha-subunit, Reverse T3) to differentiate mechanisms of complex central and peripheral HPT axis disruption.
Estimated Time:2m 30s
Question 1594Question →

A 28-year-old man presents to the clinic with a 3-year history of progressively worsening dysphagia to solid foods. He reports that food often feels "stuck in his chest," and he required emergency endoscopy 6 months ago to remove an impacted piece of meat. His medical history is notable for allergic rhinitis and childhood asthma. He has tried a 2-month course of daily omeprazole with no significant improvement in his symptoms. Physical examination is unremarkable. An upper endoscopy is performed and shows multiple stacked circular rings (trachealization), linear furrows, and scattered whitish exudates in the mid and distal esophagus. Biopsy specimens are obtained from the proximal and distal esophageal mucosa. Which of the following microscopic findings is most likely to be present on histopathologic interpretation of these biopsies?

Show answer & explanation

Answer: Squamous epithelium with >15 intraepithelial eosinophils per high-power field

Answer

Squamous epithelium with >15 intraepithelial eosinophils per high-power field
The correct answer accurately describes the defining histopathologic criterion for eosinophilic esophagitis (EoE). EoE is a chronic, immune-mediated disease characterized clinically by esophageal dysfunction (e.g., solid-food dysphagia, food impaction) and pathologically by eosinophil-predominant inflammation. The patient's history of atopy, lack of response to a proton pump inhibitor, and classic endoscopic findings (trachealization, linear furrows, white mucosal exudates) strongly suggest EoE. Biopsies taken from both the proximal and distal esophagus will reveal >15 eosinophils per high-power field, distinguishing it from GERD, which primarily affects the distal esophagus and has a much lower eosinophil count.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient is a young male with atopy (allergic rhinitis, asthma) presenting with solid-food dysphagia, a history of food impaction, and failure to respond to proton pump inhibitors (PPIs).
Identifying the demographic and symptomatic profile points toward an immune-mediated esophageal condition rather than simple acid reflux or a purely mechanical obstruction.
2
Evaluate the endoscopic findings.
Endoscopy shows stacked circular rings (trachealization), linear furrows, and whitish exudates in both the mid and distal esophagus.
These findings are classically associated with eosinophilic esophagitis (EoE), whereas strictures or esophagitis isolated to the distal esophagus would be more typical of GERD.
3
Determine the expected histopathologic findings that establish the diagnosis.
The diagnostic hallmark of EoE on esophageal biopsy is a dense intraepithelial eosinophilic infiltrate, specifically quantified as >15 eosinophils per high-power field (HPF), often accompanied by eosinophilic microabscesses (which correspond to the white exudates seen on endoscopy).
Correlating the suspected diagnosis with the definitive pathologic criteria is required to confirm EoE and differentiate it from other causes of esophagitis.

Key Concept

Eosinophilic esophagitis is diagnosed clinically by symptoms of esophageal dysfunction (dysphagia, food impaction) and histopathologically by the presence of >15 intraepithelial eosinophils per high-power field on esophageal mucosal biopsy.
Question 1595Question →

A 65-year-old man presents to the outpatient clinic for evaluation of a non-healing foot ulcer that he first noticed 4 weeks ago. His medical history is significant for poorly controlled type 2 diabetes mellitus, hypertension, and stage 4 chronic kidney disease. His current medications include insulin glargine, amlodipine, and sodium bicarbonate. He reports no fevers, chills, or systemic symptoms. Vital signs are within normal limits. Physical examination reveals a 2.5-cm, painless ulceration on the plantar aspect of the right first metatarsal head. The ulcer has a hyperkeratotic border and mild surrounding erythema. The wound base contains granulation tissue, but a sterile metal probe gently inserted into the ulcer easily contacts hard, gritty bone. Pedal pulses are palpable bilaterally. Laboratory studies show a serum creatinine of 2.9 mg/dL and an estimated glomerular filtration rate (eGFR) of 21 mL/min/1.73 m². Which of the following is the most appropriate initial diagnostic imaging study for this patient?

Show answer & explanation

Answer: Plain radiography of the right foot

Answer

Plain radiography of the right foot
The correct answer is plain radiography of the foot. In any patient with a suspected diabetic foot infection and possible osteomyelitis (strongly suggested in this scenario by the positive probe-to-bone test), plain radiography is the most appropriate initial imaging study. Even though plain radiographs have low sensitivity for detecting early acute osteomyelitis—as cortical bone destruction may not become radiographically apparent for 2 to 3 weeks—they are crucial as a first-line test. Radiographs can rapidly rule out the presence of radiopaque foreign bodies, detect soft-tissue gas indicating a potentially limb-threatening necrotizing infection, identify underlying structural deformities such as Charcot neuroarthropathy, and establish a baseline for monitoring disease progression.

Step-by-Step Solution

1
Analyze the clinical presentation and physical examination findings.
The patient is a diabetic male with a chronic foot ulcer and a positive probe-to-bone test, which is highly predictive of underlying osteomyelitis.
Establishing the primary clinical suspicion dictates the diagnostic pathway.
2
Evaluate the patient's laboratory values for potential contraindications.
The patient has stage 4 chronic kidney disease with an eGFR of 21 mL/min/1.73 m², indicating severe renal impairment.
Renal function directly impacts the safety profile of certain imaging contrast agents, particularly gadolinium.
3
Determine the most appropriate initial imaging study according to clinical guidelines.
Evidence-based guidelines mandate that plain radiography (X-ray) should be the first imaging modality performed for suspected osteomyelitis.
Plain radiographs are rapid, cost-effective, and essential for identifying soft-tissue gas, foreign bodies, or baseline bony destruction before more expensive tests are considered.

Key Concept

Plain radiography is the most appropriate initial diagnostic imaging study for all patients with suspected diabetic foot osteomyelitis. Advanced imaging, such as MRI, is reserved for cases where radiographs are negative or equivocal.
Estimated Time:1m 0s
Question 1596Question →

A 29-year-old man is evaluated in the hypertension clinic for persistently elevated blood pressure. He was diagnosed with hypertension at age 21 and is currently taking maximally tolerated doses of amlodipine, lisinopril, and chlorthalidone with poor control. He reports occasional muscle cramps but no headaches, palpitations, or diaphoresis. Family history is notable for his father, who developed severe hypertension in his twenties and died of a hemorrhagic stroke at age 42.

Blood pressure is 168/104 mm Hg and heart rate is 76/min. BMI is 24 kg/m². Physical examination reveals no abdominal bruits, striae, or abnormal fat distribution.

Laboratory results are as follows:

Laboratory StudyResultReference Range
Sodium145 mEq/L136-145 mEq/L
Potassium2.9 mEq/L3.5-5.0 mEq/L
Chloride104 mEq/L98-106 mEq/L
Bicarbonate31 mEq/L22-28 mEq/L
Creatinine0.9 mg/dL0.7-1.3 mg/dL
Plasma renin activity0.1 ng/mL/hr0.6-4.3 ng/mL/hr
Serum aldosterone32 ng/dL3-16 ng/dL

An unenhanced CT scan of the abdomen demonstrates bilateral adrenal enlargement without discrete masses. Following a 4-week therapeutic trial with low-dose oral dexamethasone, the patient's blood pressure decreases to 126/82 mm Hg and serum potassium rises to 4.3 mEq/L.

Which of the following is the most likely molecular mechanism underlying this patient's condition?

Show answer & explanation

Answer: Formation of a chimeric gene combining an ACTH-responsive promoter with the aldosterone synthase coding region

Answer

Formation of a chimeric gene combining an ACTH-responsive promoter with the aldosterone synthase coding region
The clinical presentation of primary hyperaldosteronism (hypertension, hypokalemia, elevated aldosterone, suppressed renin) that resolves with exogenous glucocorticoids (dexamethasone) is diagnostic of Glucocorticoid-Remediable Aldosteronism (Familial Hyperaldosteronism Type I). This autosomal dominant condition results from an unequal crossing-over event during meiosis between two closely linked genes on chromosome 8: CYP11B1 (which encodes 11-beta-hydroxylase, normally regulated by ACTH) and CYP11B2 (which encodes aldosterone synthase, normally regulated by angiotensin II). The resulting chimeric gene places the coding sequence for aldosterone synthase under the control of the ACTH-responsive CYP11B1 promoter. Consequently, aldosterone is secreted in an ACTH-dependent manner rather than in response to renin/angiotensin II. Dexamethasone suppresses pituitary ACTH secretion, thereby silencing the chimeric gene and normalizing aldosterone production.

Step-by-Step Solution

1
Analyze the patient's clinical and laboratory presentation.
The patient has severe, early-onset, resistant hypertension with hypokalemia, metabolic alkalosis, suppressed plasma renin activity, and elevated serum aldosterone.
These findings establish a clear diagnosis of primary hyperaldosteronism (renin-independent aldosterone hypersecretion).
2
Evaluate the imaging and therapeutic trial results.
CT shows bilateral adrenal hyperplasia. Low-dose dexamethasone completely normalizes blood pressure and potassium levels.
While bilateral idiopathic hyperplasia is a common cause of primary hyperaldosteronism, the complete resolution of the biochemical and clinical abnormalities with exogenous glucocorticoids (dexamethasone) is pathognomonic for Glucocorticoid-Remediable Aldosteronism (GRA).
3
Identify the molecular mechanism of GRA.
GRA is caused by an unequal meiotic crossing-over event that fuses the ACTH-responsive promoter of CYP11B1 to the coding sequence of CYP11B2.
This genetic alteration places aldosterone synthesis under the regulatory control of ACTH rather than angiotensin II. Exogenous dexamethasone suppresses pituitary ACTH, thereby removing the stimulus for the chimeric gene and halting excess aldosterone production.

Key Concept

Glucocorticoid-Remediable Aldosteronism (GRA) is a familial cause of primary hyperaldosteronism resulting from a chimeric gene fusion that places aldosterone synthase under ACTH regulation.
Question 1597Question →

A 32-year-old woman is evaluated in the emergency department for sudden-onset severe shortness of breath and right-sided chest pain that worsens with deep inspiration. She recently returned from a 14-hour international flight. Her medical history is unremarkable, and her only medication is an oral contraceptive pill. On physical examination, her lungs are clear to auscultation bilaterally. Her right calf is mildly swollen and tender.

Vital signs:
Temperature: 37.1∘C37.1^\circ\text{C} (98.8∘F98.8^\circ\text{F})
Blood pressure: 118/74 mmHg118/74\text{ mmHg}
Pulse: 115/min115/\text{min}
Respiratory rate: 26/min26/\text{min}

An arterial blood gas is obtained while the patient is breathing room air at sea level:
pH: 7.527.52
PaCO2PaCO_2: 28 mmHg28\text{ mmHg}
PaO2PaO_2: 56 mmHg56\text{ mmHg}
HCO3−HCO_3^-: 22 mEq/L22\text{ mEq/L}

To further evaluate the pathophysiology of her hypoxemia, the physician decides to calculate the alveolar-arterial (A-a) oxygen gradient. Assume the partial pressure of inspired oxygen (PiO2PiO_2) is 150 mmHg150\text{ mmHg} and the respiratory quotient (R) is 0.80.8.

Based on the laboratory results, what is the patient's calculated A-a gradient?

Show answer & explanation

Answer: 59

Answer

59
The correct calculation of the A-a gradient requires two steps. First, the alveolar oxygen tension (PAO2P_AO_2) is determined using the alveolar gas equation: PAO2=PiO2−PaCO2RP_AO_2 = PiO_2 - \frac{PaCO_2}{R}. Given a PiO2PiO_2 of 150 mmHg150\text{ mmHg} and an R of 0.80.8, the equation becomes 150−280.8=150−35=115 mmHg150 - \frac{28}{0.8} = 150 - 35 = 115\text{ mmHg}. Second, the measured arterial oxygen tension (PaO2P_aO_2 of 56 mmHg56\text{ mmHg}) is subtracted from the calculated PAO2P_AO_2. Thus, 115−56=59 mmHg115 - 56 = 59\text{ mmHg}. This significantly elevated A-a gradient, combined with the clinical presentation of sudden-onset pleuritic chest pain, tachypnea, and a swollen right calf following prolonged immobilization, is highly indicative of a pulmonary embolism causing ventilation-perfusion (V/Q) mismatch.

Step-by-Step Solution

1
Calculate the partial pressure of oxygen in the alveoli (PAO2P_AO_2).
PAO2=115 mmHgP_AO_2 = 115\text{ mmHg}
The alveolar gas equation estimates PAO2P_AO_2 as PiO2−PaCO2RPiO_2 - \frac{PaCO_2}{R}. Substituting the given values: PAO2=150−280.8=150−35=115 mmHgP_AO_2 = 150 - \frac{28}{0.8} = 150 - 35 = 115\text{ mmHg}.
2
Calculate the alveolar-arterial (A-a) oxygen gradient.
59 mmHg59\text{ mmHg}
The A-a gradient is the difference between the alveolar and arterial oxygen tensions (PAO2−PaO2P_AO_2 - P_aO_2). Substituting the calculated and measured values: 115−56=59 mmHg115 - 56 = 59\text{ mmHg}.

Key Concept

The alveolar-arterial (A-a) oxygen gradient helps differentiate causes of hypoxemia; an elevated gradient (> 10-15 mmHg in young adults) in the setting of respiratory alkalosis strongly suggests ventilation-perfusion (V/Q) mismatch, commonly seen in pulmonary embolism.
Estimated Time:1m 30s
Question 1598Question →

Match each patient's clinical presentation and care setting with the single most appropriate initial or definitive diagnostic imaging modality.

Click a left item, then click its matching right item

Items

Emergency department presentation of a 35-year-old man with abrupt onset of severe, unilateral scrotal pain, localized swelling, and an absent cremasteric reflex.
Emergency department presentation of a 55-year-old woman with a sudden-onset 'thunderclap' headache, photophobia, and neck stiffness within 4 hours of symptom onset.
Outpatient gastroenterology clinic presentation of a 28-year-old woman with known Crohn's disease complaining of progressive perianal pain and induration, concerning for a deep tissue fistula.
Primary care clinic presentation of a 65-year-old man with a recent onset of painless jaundice, acholic stools, and a palpable, non-tender right upper quadrant abdominal mass, requiring an initial evaluation step.

Matches

Show answer & explanation

Answer

The patient with abrupt scrotal pain requires a Color Doppler ultrasonography of the scrotum; the patient with a 'thunderclap' headache requires a non-contrast computed tomography of the head; the patient with Crohn's disease and perianal pain requires magnetic resonance imaging of the pelvis; and the patient with painless jaundice requires ultrasonography of the right upper quadrant as the initial test.
Each clinical scenario presents a classic diagnostic challenge where the choice of imaging is critical for timely and accurate patient management. Testicular torsion requires immediate blood flow evaluation via Doppler ultrasound. Subarachnoid hemorrhage is a neurologic emergency best initially evaluated by a non-contrast head CT to detect acute blood. Complex perianal fistulas in Crohn's disease require precise soft-tissue anatomical mapping, making pelvic MRI the gold standard. Finally, the initial evaluation of painless jaundice begins with a right upper quadrant ultrasound to differentiate between intrahepatic and extrahepatic causes of biliary obstruction, prior to advanced cross-sectional imaging.

Step-by-Step Solution

1
Analyze each clinical vignette to identify the primary suspected diagnosis based on the key signs, symptoms, and the clinical setting.
The suspected diagnoses are testicular torsion, subarachnoid hemorrhage, perianal fistula from Crohn's disease, and malignant biliary obstruction, respectively.
Accurate recognition of the underlying pathology is the prerequisite for selecting the appropriate diagnostic pathway.
2
Determine the optimal, evidence-based imaging modality tailored to both the suspected pathology and the chronological sequence of evaluation (e.g., initial versus definitive staging).
Identified Doppler US for torsion, non-contrast head CT for acute hemorrhage, pelvic MRI for soft-tissue fistula mapping, and RUQ ultrasound for initial biliary evaluation.
Different tissue types and diagnostic urgencies require specific imaging techniques (e.g., ultrasound for flow and biliary tracts, non-contrast CT for acute intracranial hemorrhage, MRI for detailed pelvic soft tissue).
3
Match each identified imaging modality to its corresponding patient presentation.
All four clinical presentations are correctly paired with their respective optimal imaging study.
This confirms mastery of diagnostic imaging selection guidelines.

Key Concept

Selecting the most appropriate initial or definitive imaging modality based on the specific clinical presentation, suspected diagnosis, and evidence-based guidelines.
Question 1599Question →

A 34-year-old woman presents to the emergency department with a rapidly expanding hematoma on her right thigh and extensive ecchymoses on her arms and torso. She delivered a healthy infant 4 weeks ago via an uncomplicated vaginal delivery. She has no personal or family history of bleeding disorders and had no excessive bleeding during childbirth, prior menses, or dental procedures. Her only medication is a daily prenatal vitamin. Vital signs are within normal limits. Physical examination reveals a 12-cm tense, tender hematoma on the right anterior thigh.

Laboratory evaluation shows:
- Hemoglobin: 10.2 g/dL
- Platelet count: 280,000/mm³
- Prothrombin time (PT): 12 seconds (normal: 11-14 seconds)
- Activated partial thromboplastin time (aPTT): 68 seconds (normal: 25-35 seconds)
- Thrombin time: 14 seconds (normal: 12-14 seconds)
- Fibrinogen: 350 mg/dL (normal: 200-400 mg/dL)

A 1:1 mixing study with normal pooled plasma is performed. The aPTT immediately corrects to 30 seconds. However, after incubating the mixture for 2 hours at 37°C, the aPTT is 62 seconds.

Which of the following is the most appropriate next step in laboratory evaluation?

Show answer & explanation

Answer: Measurement of factor VIII activity and a Bethesda assay

Answer

Measurement of factor VIII activity and a Bethesda assay
The correct answer involves quantifying the factor VIII activity and the inhibitor titer. The patient has acquired hemophilia A, a rare but life-threatening autoimmune disorder caused by autoantibodies against factor VIII. It classically occurs in older adults, patients with underlying autoimmune diseases, or in the postpartum period (usually 1-4 months after delivery). The laboratory hallmark is an isolated prolonged aPTT with a normal PT. In a mixing study, acquired factor VIII inhibitors exhibit a unique time- and temperature-dependent pattern: the aPTT initially corrects (mimicking a factor deficiency) but prolongs again after a 1-to-2-hour incubation at 37°C. The most appropriate next step to confirm the diagnosis is to measure specific factor VIII activity and quantify the inhibitor using a Bethesda assay.

Step-by-Step Solution

1
Analyze the initial coagulation panel results.
The patient has an isolated prolongation of the activated partial thromboplastin time (aPTT) with a normal prothrombin time (PT), thrombin time, and platelet count.
To localize the coagulation defect to the intrinsic pathway (factors VIII, IX, XI, XII) or identify the presence of a circulating inhibitor.
2
Interpret the 1:1 mixing study results.
The immediate correction of the aPTT followed by significant prolongation after a 2-hour incubation at 37°C indicates the presence of a time- and temperature-dependent inhibitor.
To differentiate between a simple factor deficiency (which shows sustained correction) and an immediate or time-dependent inhibitor.
3
Correlate the laboratory findings with the clinical presentation.
A time-dependent inhibitor in a postpartum patient presenting with sudden, severe soft tissue bleeding is highly characteristic of an acquired factor VIII autoantibody (acquired hemophilia A).
To formulate the most likely clinical diagnosis driving the need for specific confirmatory testing.
4
Determine the most appropriate confirmatory laboratory test sequence.
The next step is to measure specific factor VIII activity levels (which will be low) and quantify the inhibitor titer using a Bethesda assay.
To definitively confirm the diagnosis of acquired hemophilia A and guide subsequent immunosuppressive and hemostatic therapies.

Key Concept

Laboratory evaluation and diagnosis of acquired hemophilia A using a mixing study algorithm
Question 1600Question →

A 64-year-old man presents to the emergency department with a 4-day history of severe, crampy abdominal pain and 8 to 10 watery, non-bloody bowel movements daily. He was diagnosed with metastatic non-small cell lung cancer 3 months ago. Genomic testing of his tumor revealed high expression of a ligand that binds to an inhibitory T-cell receptor. Based on these findings, he recently began targeted monoclonal antibody therapy, receiving his last infusion 10 days ago. His temperature is 37.9°C (100.2°F), blood pressure is 102/65 mm Hg, and pulse is 112/min. Physical examination reveals dry mucous membranes and diffuse abdominal tenderness without rigidity, rebound, or guarding. Laboratory studies show a serum creatinine of 1.4 mg/dL (baseline 0.9 mg/dL) and a white blood cell count of 11,500/mm³. Rapid stool testing for Clostridioides difficile toxin is negative. Which of the following is the most appropriate next step in management?

Show answer & explanation

Answer: Initiate intravenous methylprednisolone and permanently discontinue the targeted monoclonal antibody therapy

Answer

Initiate intravenous methylprednisolone and permanently discontinue the targeted monoclonal antibody therapy
The correct intervention involves halting the immunotherapy permanently and administering systemic steroids. The patient's history of targeted therapy for a tumor expressing a ligand for an inhibitory T-cell receptor indicates he is taking a PD-1 or PD-L1 inhibitor. These immune checkpoint inhibitors restore T-cell-mediated anti-tumor immunity but frequently disrupt self-tolerance, causing autoimmune toxicities known as immune-related adverse events (irAEs). This patient is presenting with Grade 3 immune-mediated colitis (defined as an increase of ≥7 stools per day over baseline, or symptoms interfering with activities of daily living). Standard management for Grade 3 or 4 irAEs requires immediate hospitalization, initiation of high-dose intravenous corticosteroids (such as methylprednisolone), and permanent discontinuation of the checkpoint inhibitor.

Step-by-Step Solution

1
Identify the mechanism of the patient's antineoplastic therapy.
The tumor expresses a ligand binding to an inhibitory T-cell receptor (PD-L1), indicating the patient is receiving an immune checkpoint inhibitor (e.g., pembrolizumab or nivolumab).
Identifying the drug class is necessary to anticipate its specific, mechanism-based adverse effect profile.
2
Evaluate the clinical severity of the patient's gastrointestinal presentation.
The patient has 8 to 10 watery stools daily along with dehydration and acute kidney injury, which classifies as Grade 3 (severe) colitis.
Toxicity grading directly dictates the algorithmic management of immune-related adverse events.
3
Determine the appropriate intervention for severe immune-mediated colitis.
Administration of systemic high-dose corticosteroids and the permanent cessation of the immunotherapy.
Grade 3 and 4 immune-mediated toxicities require immediate suppression of the overactive immune response to prevent life-threatening bowel perforation or toxic megacolon.

Key Concept

Severe (Grade 3 or 4) immune-mediated colitis secondary to immune checkpoint inhibitors (e.g., PD-1/PD-L1 antagonists) requires prompt administration of systemic high-dose corticosteroids and permanent discontinuation of the offending immunotherapy agent.
Estimated Time:1m 15s
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