Tüm alıştırma soruları

4736 soru

Soru 1621Soru →

Neurological physical examination is critical for localizing acute ischemic strokes. Match each constellation of physical examination findings with its most likely corresponding occluded vascular territory.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Ipsilateral ptosis and miosis, hoarseness, absent gag reflex, and contralateral body loss of pain and temperature sensation
Ipsilateral tongue deviation upon protrusion, contralateral hemiparesis, and contralateral loss of proprioception
Ipsilateral ptosis, resting 'down and out' eye position with mydriasis, and contralateral hemiparesis
Ipsilateral complete facial paralysis, inability to abduct the eye, and contralateral hemiparesis
Contralateral lower extremity weakness and sensory loss, with relative sparing of the upper extremity, accompanied by urinary incontinence

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The correct matches correlate classic neurological examination findings to their respective vascular territories: Lateral Medullary (Wallenberg) syndrome to PICA, Medial Medullary syndrome to ASA, Midbrain (Weber) syndrome to PCA paramedian branches, Caudal Pontine syndrome to Basilar paramedian branches, and medial frontoparietal cortical strokes to ACA.
Crossed signs (ipsilateral cranial nerve palsies and contralateral long tract deficits) indicate a brainstem lesion. CN III localization points to the midbrain (PCA paramedian branches). CN VI/VII localizations point to the pons (Basilar paramedian branches). CN XII localization points to the medial medulla (ASA), while the nucleus ambiguus and sympathetic fibers point to the lateral medulla (PICA). Cortical strokes lack crossed cranial nerve signs; ACA strokes preferentially cause contralateral lower extremity weakness and sensory loss, along with incontinence, due to medial cortex involvement.

Adım Adım Çözüm

1
Analyze the cranial nerve deficits to determine the rostrocaudal level of the brainstem lesion.
Oculomotor (CN III) deficits localize to the midbrain. Abducens (CN VI) and Facial (CN VII) deficits localize to the pons. Glossopharyngeal (CN IX), Vagus (CN X), and Hypoglossal (CN XII) deficits localize to the medulla.
Cranial nerve nuclei have strict vertical anatomical positions within the brainstem.
2
Evaluate the long tract signs (motor and sensory) to establish the medial-lateral position of the lesion.
Corticospinal tract (motor) and medial lemniscus (proprioception) deficits indicate a medial lesion. Spinothalamic tract (pain/temperature) and sympathetic chain (Horner syndrome) deficits indicate a lateral lesion.
Vascular supply to the brainstem is strictly segregated into paramedian (medial structures) and circumferential (lateral structures) arterial branches.
3
Synthesize the neuroanatomical localization to deduce the occluded vascular territory.
A medial medullary lesion maps to the ASA, a lateral medullary lesion to the PICA, a medial pontine lesion to basilar paramedian branches, and a midbrain lesion to PCA paramedian branches. Deficits sparing cranial nerves but disproportionately affecting the contralateral leg map to the ACA.
Understanding distinct cerebrovascular territories is necessary to establish the etiology of the physical examination findings.

Anahtar Kavram

Neuroanatomical localization of acute ischemic strokes using cranial nerve and long tract physical examination findings
Tahmini Süre:1m 30s
Soru 1622Soru →

A physician is managing a 45-year-old female patient who presents with resistant hypertension and spontaneous hypokalemia. Diagnostic testing reveals an elevated plasma aldosterone concentration to plasma renin activity ratio, and abdominal imaging confirms a unilateral adrenal adenoma. The patient's condition results in excessive sodium reabsorption in the distal nephron. Arrange the following cellular events in the correct chronological sequence to describe the physiological mechanism of action for the hormone overproduced in this condition.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence begins with the hormone entering the cell via diffusion, followed by cytosolic receptor binding, nuclear translocation, gene transcription, and finally the insertion of sodium channels into the membrane.
Aldosterone is a lipophilic steroid hormone that exerts its effects primarily via a genomic mechanism. First, it diffuses across the basolateral membrane of the principal cells in the renal collecting duct. Second, it binds to the cytosolic mineralocorticoid receptor, inducing a conformational change and the shedding of associated chaperone proteins. Third, this active complex translocates into the nucleus. Fourth, it binds to specific DNA sequences to promote the transcription of aldosterone-induced proteins, particularly SGK1. Finally, SGK1 inhibits the ubiquitin ligase Nedd4-2, preventing the degradation of epithelial sodium channels (ENaC) and resulting in their increased insertion into the apical membrane.

Adım Adım Çözüm

1
Identify the primary hormone involved based on the clinical presentation.
The patient has primary hyperaldosteronism (Conn syndrome), indicating that the hormone driving the pathology is aldosterone.
Identifying the hormone is required to determine its specific intracellular signaling pathway.
2
Determine the biochemical class of the hormone.
Aldosterone is a steroid hormone (mineralocorticoid).
Steroid hormones share a common genomic mechanism of action, differentiating them from peptide hormones that bind to extracellular cell-surface receptors.
3
Sequence the steroid hormone genomic signaling pathway.
Cellular diffusion -> Cytosolic receptor binding -> Nuclear translocation -> Gene transcription (AIPs/SGK1) -> Physiological effect (ENaC insertion).
This is the classic multi-step mechanism required for steroid hormones to exert their physiological effects on target tissues.

Anahtar Kavram

Steroid hormone mechanism of action (Aldosterone)
Soru 1623Soru →

A 6262-year-old man comes to the clinic to review the results of a recent imaging study. Two weeks ago, he was evaluated in the emergency department for severe left-sided flank pain radiating to the groin. A non-contrast computed tomography (CT) scan of the abdomen and pelvis demonstrated a 44-mm left ureteral calculus, which he subsequently passed. The CT scan also incidentally revealed a 3.23.2-cm right adrenal nodule. The nodule is well-circumscribed and homogeneous, with an unenhanced attenuation of 88 Hounsfield units. The patient has no history of malignancy and reports feeling well since passing the stone. Medical history is significant for hypertension and osteoarthritis. His medications include lisinopril, hydrochlorothiazide, and occasional ibuprofen. Blood pressure is 142/88142/88 mm Hg, pulse is 7676/min, and body mass index is 2626 kg/m 2^2. Physical examination is unremarkable, with no supraclavicular fat pads, abdominal striae, or skin thinning. Serum potassium was 4.14.1 mEq/L in the emergency department.

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

Cevabı ve açıklamayı göster

Cevap: 1-mg overnight dexamethasone suppression test, plasma free metanephrines, and plasma aldosterone-to-renin ratio

Cevap

The most appropriate next step is to order a 1-mg overnight dexamethasone suppression test, plasma free metanephrines, and a plasma aldosterone-to-renin ratio.
This patient has an adrenal incidentaloma, defined as an adrenal mass ≥1\geq 1 cm discovered serendipitously on imaging performed for reasons other than suspected adrenal disease. All patients with an adrenal incidentaloma require a comprehensive biochemical evaluation to rule out hormonal hypersecretion, regardless of the presence or absence of overt clinical symptoms. The initial screening panel must include tests to rule out hypercortisolism (e.g., 11-mg overnight dexamethasone suppression test) and pheochromocytoma (e.g., plasma free metanephrines or 2424-hour urine fractionated metanephrines). In addition, for patients with hypertension or hypokalemia, screening for primary aldosteronism is required using the plasma aldosterone-to-renin ratio (ARR). Because this patient has a history of hypertension, he requires the complete triad of screening tests.

Adım Adım Çözüm

1
Identify the clinical problem from the vignette.
The patient has an incidentally discovered 3.23.2-cm adrenal mass with benign imaging characteristics (<10<10 HU) and concurrent hypertension.
Recognizing the definition and clinical context of an adrenal incidentaloma dictates the subsequent standard diagnostic algorithm.
2
Determine the necessary baseline biochemical evaluation for all adrenal incidentalomas.
All patients, regardless of symptoms or imaging phenotype, require screening for subclinical hypercortisolism (e.g., 11-mg dexamethasone suppression test) and pheochromocytoma (e.g., plasma free metanephrines).
Subclinical hyperfunctioning adenomas are common and can cause significant metabolic morbidity or life-threatening perioperative complications if missed.
3
Determine if additional specific biochemical testing is indicated based on patient comorbidities.
The patient has hypertension, which mandates additional screening for primary aldosteronism using the plasma aldosterone-to-renin ratio.
Primary aldosteronism is a common cause of secondary hypertension and must be evaluated in incidentalomas accompanied by elevated blood pressure, even if serum potassium is normal.

Anahtar Kavram

All adrenal incidentalomas require biochemical screening for hypercortisolism and pheochromocytoma. Additional screening for primary aldosteronism (aldosterone-to-renin ratio) is required if the patient has hypertension or hypokalemia.
Soru 1624Soru →

A 35-year-old woman comes to the clinic reporting progressive fatigue, diffuse muscle weakness, and excessive thirst for the past three weeks. Her medical history is notable for Sjögren syndrome and two episodes of calcium phosphate nephrolithiasis over the past five years. She currently takes no medications. Her temperature is 37.0°C (98.6°F), blood pressure is 110/70 mmHg, pulse is 88/min, and respiratory rate is 16/min. Physical examination reveals dry mucous membranes but is otherwise unremarkable. Laboratory studies are obtained as shown below:

Serum Laboratory Results:
TestResultReference Range
Sodium (Na⁺)139 mEq/L136-145 mEq/L
Potassium (K⁺)2.7 mEq/L3.5-5.0 mEq/L
Chloride (Cl⁻)112 mEq/L98-106 mEq/L
Bicarbonate (HCO₃⁻)15 mEq/L22-28 mEq/L
Blood urea nitrogen (BUN)14 mg/dL7-20 mg/dL
Creatinine0.9 mg/dL0.6-1.2 mg/dL
Glucose88 mg/dL70-100 mg/dL
Urine Laboratory Results:
TestResult
pH6.5
Sodium (Na⁺)40 mEq/L
Potassium (K⁺)25 mEq/L
Chloride (Cl⁻)50 mEq/L
Urea Nitrogen (UUN)420 mg/dL
Glucose0 mg/dL
Measured Osmolality310 mOsm/kg H₂O

Based on the laboratory data provided, what is the patient's calculated urine osmolar gap? (Enter the numerical value only)

Cevabı ve açıklamayı göster

Cevap: 30

Cevap

30
The patient has a normal anion gap metabolic acidosis (NAGMA) secondary to distal (type 1) renal tubular acidosis, which is strongly associated with Sjögren syndrome and calcium phosphate nephrolithiasis. In the workup of NAGMA, it is critical to determine if the kidneys are appropriately secreting acid in the form of ammonium (NH4+NH_4^+). The urine osmolar gap (UOG) is the most accurate indirect measure of urinary ammonium. The gap is the difference between the measured urine osmolality and the calculated urine osmolality.

The formula for calculated urine osmolality is: Calculated Uosm=2×(Na++K+)+UUN2.8+Glucose18 \text{Calculated U}_{\text{osm}} = 2 \times (\text{Na}^+ + \text{K}^+) + \frac{\text{UUN}}{2.8} + \frac{\text{Glucose}}{18}

Plugging in the patient's values:
Calculated Uosm=2×(40+25)+4202.8+0 \text{Calculated U}_{\text{osm}} = 2 \times (40 + 25) + \frac{420}{2.8} + 0
Calculated Uosm=2×65+150=130+150=280 mOsm/kg \text{Calculated U}_{\text{osm}} = 2 \times 65 + 150 = 130 + 150 = 280 \text{ mOsm/kg}

The UOG is the measured osmolality minus the calculated osmolality:
310−280=30 mOsm/kg 310 - 280 = 30 \text{ mOsm/kg}

A UOG of less than 40-50 mOsm/kg indicates low urinary ammonium excretion, confirming a renal etiology for the acidosis (RTA), whereas a UOG > 100 mOsm/kg would indicate adequate ammonium excretion (suggesting gastrointestinal bicarbonate loss).

Adım Adım Çözüm

1
Calculate the serum anion gap.
Serum AG = 139 - (112 + 15) = 12 mEq/L.
To classify the metabolic acidosis as a normal anion gap metabolic acidosis (NAGMA), which dictates the next step in laboratory interpretation.
2
Apply the calculated urine osmolality formula.
Calculated U_osm = 2 * (40 + 25) + (420 / 2.8) + (0 / 18) = 130 + 150 = 280 mOsm/kg.
To estimate the osmolar contribution of the measured major urinary solutes (sodium, potassium, urea, and glucose).
3
Calculate the urine osmolar gap.
Gap = 310 (Measured) - 280 (Calculated) = 30 mOsm/kg.
The difference between measured and calculated osmolality reflects unmeasured osmoles, which in the urine primarily consist of ammonium and its accompanying anions.

Anahtar Kavram

The urine osmolar gap is used to indirectly measure urinary ammonium excretion in the evaluation of a normal anion gap metabolic acidosis.
Soru 1625Soru →

Match each characteristic thoracic imaging finding described below with its most likely associated clinical condition.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Enlarged, globular cardiac silhouette with a 'water bottle' configuration on a PA chest radiograph
Shallow, wedge-shaped peripheral consolidation with its base against the pleural surface on a chest radiograph
Abnormal radiolucency extending deeply into the costophrenic angle on a supine anteroposterior chest radiograph
Bilateral, symmetric, perihilar airspace opacities that spare the peripheral lung zones on a chest radiograph

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The 'water bottle' silhouette matches a large pericardial effusion; the wedge-shaped consolidation matches a pulmonary embolism with infarction; the abnormal radiolucency in the costophrenic angle matches a supine pneumothorax; and the perihilar opacities match acute cardiogenic pulmonary edema.
Each radiographic finding is a pathognomonic sign for a specific acute cardiopulmonary pathology. The 'water bottle' silhouette represents fluid accumulation in the pericardial space. 'Hampton's hump' reflects localized lung necrosis and hemorrhage due to a pulmonary embolus. The 'deep sulcus sign' indicates pleural air collecting in the nondependent costophrenic recess in a supine patient. The 'batwing' pattern reflects fluid shifting into the central alveolar spaces due to elevated pulmonary venous pressure.

Adım Adım Çözüm

1
Analyze the description of the 'water bottle' cardiac silhouette.
Identify this as representing an accumulation of fluid in the pericardial sac.
Pericardial fluid settles dependently, rounding the heart borders and eliminating normal anatomical indentations.
2
Evaluate the wedge-shaped peripheral consolidation.
Associate this finding with pulmonary infarction due to a distal pulmonary embolism.
Vascular occlusion leads to downstream lung ischemia and hemorrhage, which takes a wedge shape corresponding to the affected vascular territory.
3
Assess the abnormal lucency in the costophrenic angle on a supine film.
Correlate this 'deep sulcus sign' with a pneumothorax in a recumbent patient.
In a supine position, free pleural air rises to the highest point in the hemithorax, which is anterior and basal, deepening the sulcus rather than forming an apical line.
4
Examine the description of bilateral perihilar 'batwing' opacities.
Link this structural pattern to acute cardiogenic pulmonary edema.
Elevated hydrostatic pressure causes fluid to extravagate preferentially in the central, perihilar alveolar spaces before extending peripherally.

Anahtar Kavram

Classic Thoracic Imaging Signs
Soru 1626Soru →

A 48-year-old man who recently emigrated from Southeast Asia presents to the clinic complaining of progressive abdominal swelling, bilateral ankle swelling, and generalized fatigue over the past 4 months. He recalls having a chronic cough and night sweats a few years ago that resolved without formal medical treatment. His temperature is 37.1∘C37.1^{\circ}\text{C} (98.8∘F98.8^{\circ}\text{F}), blood pressure is 118/78 mm Hg118/78\text{ mm Hg}, and pulse is 88 /min88\text{ /min}. On physical examination, the jugular veins are distended to 11 cm H2O11\text{ cm H}_2\text{O} while the patient is sitting at a 45∘45^{\circ} angle. The jugular venous pressure paradoxically increases during deep inspiration. Careful inspection of the neck veins reveals a rapid, deep yy descent. Cardiac auscultation reveals a high-pitched, early diastolic sound heard best at the left sternal border. The lungs are clear to auscultation bilaterally. Abdominal examination demonstrates shifting dullness. Which of the following is the most likely diagnosis?

Cevabı ve açıklamayı göster

Cevap: Constrictive pericarditis

Cevap

Constrictive pericarditis
The correct answer is constrictive pericarditis. This condition, often caused by tuberculosis in endemic areas, creates a rigid, fibrotic pericardial shell. This noncompliant casing prevents the right heart from accommodating the normal increase in venous return during inspiration, resulting in a paradoxical rise in jugular venous pressure (Kussmaul sign). During early diastole, ventricular filling is exceptionally rapid (producing a deep, steep yy descent on the JVP tracing) until the expanding ventricle hits the rigid pericardium. This sudden halt in filling produces a characteristic high-pitched, early diastolic sound known as a pericardial knock.

Adım Adım Çözüm

1
Identify the clinical syndrome from the patient's presentation.
The patient has signs of severe right-sided heart failure (elevated jugular venous pressure, ascites, peripheral edema) with a history suggesting prior untreated tuberculosis.
Establishing the broad syndromic category narrows the differential diagnosis to causes of right heart failure.
2
Analyze the specific jugular venous pulse (JVP) findings.
The paradoxical rise in JVP with inspiration is Kussmaul sign. The rapid, deep yy descent is Friedreich sign. Both point to restricted right ventricular filling.
Specific JVP waveforms differentiate between pericardial, myocardial, and valvular causes of right heart failure.
3
Interpret the cardiac auscultation findings.
The high-pitched, early diastolic sound is a pericardial knock, characteristic of rapid ventricular filling abruptly halting against a rigid, scarred pericardium.
The timing and pitch of the extra heart sound help differentiate between constriction (knock) and restriction (S3S_3 or S4S_4).
4
Synthesize the findings to establish the diagnosis.
The combination of Kussmaul sign, a rapid yy descent, and a pericardial knock in a patient from an endemic area with probable prior tuberculosis firmly diagnoses constrictive pericarditis.
Combining multiple distinct physical examination findings prevents premature diagnostic closure on similar mimicking conditions.

Anahtar Kavram

The classic physical examination findings for constrictive pericarditis include an elevated jugular venous pressure that rises with inspiration (Kussmaul sign), a prominent and rapid yy descent (Friedreich sign), and a high-pitched early diastolic sound (pericardial knock).
Tahmini Süre:1m 30s
Soru 1627Soru →

For each of the following clinical scenarios requiring targeted biologic therapy, select the precise immunopathologic mechanism of the most appropriate therapeutic agent.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

A 32-year-old woman with highly active relapsing-remitting multiple sclerosis requires escalation of therapy. Serological testing for the John Cunningham (JC) virus is negative.
A 45-year-old man with medically refractory chronic spontaneous urticaria continues to experience daily wheals and severe pruritus despite maximum tolerated doses of second-generation H1-antihistamines.
A 28-year-old woman is diagnosed with severe fistulizing Crohn disease and concurrent moderate-to-severe plaque psoriasis. She requires induction and maintenance therapy.
A 55-year-old man with newly diagnosed microscopic polyangiitis and rapidly progressive glomerulonephritis requires non-glucocorticoid induction therapy.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The correct matches align each specific autoimmune or inflammatory condition with the precise molecular target of its corresponding first-line or escalation biologic agent: MS with alpha-4 integrin blockade, chronic urticaria with IgE binding, Crohn/psoriasis with IL-12/23 p40 inhibition, and microscopic polyangiitis with CD20 depletion.
Each clinical presentation requires a specific immunomodulator whose mechanism precisely targets the underlying pathophysiology of the disease. Natalizumab blocks leukocyte CNS entry in MS. Omalizumab neutralizes IgE in chronic urticaria. Ustekinumab halts the IL-12/23 inflammatory cascade in Crohn disease and psoriasis. Rituximab depletes the autoantibody-producing B cells in ANCA-associated vasculitis.

Adım Adım Çözüm

1
Identify the indicated biologic agent for each specific clinical scenario.
Natalizumab is indicated for the MS patient. Omalizumab is indicated for the chronic urticaria patient. Ustekinumab is indicated for the patient with Crohn disease and psoriasis. Rituximab is indicated for the patient with microscopic polyangiitis.
Establishing the correct drug based on clinical presentation and guidelines is necessary before identifying its molecular mechanism.
2
Map each identified agent to its immunopharmacologic mechanism of action.
Natalizumab blocks alpha-4 integrin; Omalizumab binds circulating IgE; Ustekinumab targets the IL-12/23 p40 subunit; Rituximab depletes CD20+ B cells.
Demonstrates foundational knowledge of how targeted immunotherapies modulate specific immune cascades and pathways.

Anahtar Kavram

Understanding the precise immunologic targets of monoclonal antibodies is essential for selecting appropriate therapies and anticipating specific adverse effects or contraindications (e.g., PML risk with alpha-4 integrin blockade).
Soru 1628Soru →

A physician is reviewing laboratory results for several patients presenting with microcytic anemia (Mean Corpuscular Volume < 80 fL). Match the following serum iron and hematologic profiles to their most likely diagnostic etiology.

Reference ranges:
Serum iron: 60-170 µg/dL
Total iron-binding capacity (TIBC): 240-450 µg/dL
Ferritin: 15-200 ng/mL
Transferrin saturation: 20-50%
Red Cell Distribution Width (RDW): 11.5-14.5%

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Serum iron: 35 µg/dL, TIBC: 480 µg/dL, Ferritin: 8 ng/mL, Transferrin saturation: 7%
Serum iron: 40 µg/dL, TIBC: 210 µg/dL, Ferritin: 350 ng/mL, Transferrin saturation: 19%
Serum iron: 185 µg/dL, TIBC: 280 µg/dL, Ferritin: 450 ng/mL, Transferrin saturation: 66%
Serum iron: 95 µg/dL, TIBC: 310 µg/dL, Ferritin: 110 ng/mL, Transferrin saturation: 30%, RDW: 12%

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Profile 1 matches Iron deficiency anemia; Profile 2 matches Anemia of chronic inflammation; Profile 3 matches Sideroblastic anemia; Profile 4 matches Beta-thalassemia minor.
Interpreting microcytic anemias requires analyzing the interplay between serum iron, TIBC, and ferritin. Iron deficiency is characterized by depleted stores (low ferritin) and compensatory increased transferrin (high TIBC). Anemia of chronic inflammation is driven by hepcidin, which sequesters iron in macrophages (high ferritin) and decreases transferrin synthesis (low TIBC). Sideroblastic anemia involves an inability to incorporate iron into protoporphyrin, leading to systemic iron accumulation (high serum iron, high ferritin). Beta-thalassemia is a primary globin defect; therefore, iron studies remain normal, and patients typically present with uniform microcytosis (normal RDW).

Adım Adım Çözüm

1
Evaluate ferritin levels as the primary indicator of total body iron stores.
A distinctly low ferritin uniquely identifies iron deficiency, while high or normal levels point to chronic disease, sideroblastic anemia, or thalassemia.
Ferritin is the most specific initial test to differentiate true systemic iron deficiency from other causes of microcytic anemia.
2
Assess TIBC and transferrin saturation in patients presenting with normal or high ferritin levels.
A low TIBC with high ferritin indicates anemia of chronic inflammation. Conversely, high transferrin saturation with high ferritin points to sideroblastic anemia or iron overload.
Hepcidin upregulation in chronic inflammation decreases transferrin (TIBC), whereas defective heme synthesis in sideroblastic anemia leaves excess iron unbound in serum.
3
Review the red cell distribution width (RDW) in the context of entirely normal iron studies.
Normal iron studies accompanied by a normal RDW in the setting of isolated microcytosis is indicative of thalassemia trait.
Thalassemia is a primary globin chain synthesis defect, meaning iron metabolism remains unaffected, and red cell sizing is uniformly microcytic without the size variation seen in early iron deficiency.

Anahtar Kavram

Differential diagnosis of microcytic anemia using serum iron studies.
Soru 1629Soru →

A 28-year-old woman is brought to the emergency department by her roommate due to confusion, ringing in her ears, and rapid breathing for the past 66 hours. She has also had multiple episodes of non-bilious vomiting. The roommate reports finding an empty bottle of over-the-counter pain medication in their shared bathroom. On physical examination, the patient appears agitated and diaphoretic. Vital signs are temperature 37.8∘37.8^\circ C (100.0∘100.0^\circ F), blood pressure 110/70110/70 mm Hg, heart rate 112112/min, and respiratory rate 2828/min.

Laboratory studies show:

Serum chemistry
Sodium: 140140 mEq/L
Potassium: 3.43.4 mEq/L
Chloride: 9696 mEq/L
Bicarbonate: 1414 mEq/L
Blood urea nitrogen: 2020 mg/dL
Creatinine: 1.21.2 mg/dL

Arterial blood gas (room air)
pH: 7.457.45
PaCO 2_2: 2020 mm Hg
PaO 2_2: 9696 mm Hg

Which of the following is the most accurate interpretation of this patient's acid-base status?

Cevabı ve açıklamayı göster

Cevap: Mixed primary elevated anion gap metabolic acidosis, primary respiratory alkalosis, and primary metabolic alkalosis

Cevap

Mixed primary elevated anion gap metabolic acidosis, primary respiratory alkalosis, and primary metabolic alkalosis
The correct answer identifies a triple acid-base disorder based on systematic interpretation of the lab values. First, the anion gap is 3030 mEq/L (140−[96+14]140 - [96 + 14]), confirming a primary elevated anion gap metabolic acidosis. Second, Winter's formula demonstrates an expected PaCO 2_2 of 2929 mm Hg; the actual PaCO 2_2 of 2020 mm Hg falls below this expected range, confirming a concurrent primary respiratory alkalosis. Finally, the delta-delta gap calculation gives a corrected bicarbonate of 3232 mEq/L (14+[30−12]14 + [30 - 12]). Because this corrected value exceeds normal levels (2424-2626 mEq/L), an independent primary metabolic alkalosis is also confirmed.

Adım Adım Çözüm

1
Calculate the serum anion gap to evaluate for metabolic acidosis.
Anion Gap (AG) = Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-) = 140−(96+14)=30140 - (96 + 14) = 30 mEq/L.
An elevated AG (normal 88-1212 mEq/L) confirms the presence of a primary high anion gap metabolic acidosis, which in this case is caused by salicylate toxicity and resulting lactic acidosis.
2
Apply Winter's formula to determine the expected respiratory compensation for the metabolic acidosis.
Expected PaCO 2_2 = (1.5×HCO3−)+8=(1.5×14)+8=29±2(1.5 \times HCO_3^-) + 8 = (1.5 \times 14) + 8 = 29 \pm 2 mm Hg.
Because the measured PaCO 2_2 (2020 mm Hg) is significantly lower than the expected range (2727-3131 mm Hg), an independent primary respiratory alkalosis is also present (due to direct salicylate stimulation of the medullary respiratory center).
3
Perform a delta-delta (Δ/Δ\Delta/\Delta) gap calculation to reveal any hidden metabolic disorders.
Δ\Delta AG = 30−12=1830 - 12 = 18 mEq/L. Corrected HCO3−HCO_3^- = Measured HCO3−HCO_3^- + Δ\Delta AG = 14+18=3214 + 18 = 32 mEq/L.
Since the corrected HCO3−HCO_3^- (3232 mEq/L) is greater than the normal baseline of 2424-2626 mEq/L, a concurrent primary metabolic alkalosis must be present, which is clinically consistent with her history of severe vomiting.

Anahtar Kavram

Patients with severe salicylate toxicity frequently present with a mixed primary high anion gap metabolic acidosis and primary respiratory alkalosis; concurrent vomiting can add a third primary disorder (metabolic alkalosis), which is unmasked by calculating the delta-delta gap.
Soru 1630Soru →

Match each clinical presentation to the most appropriate initial or confirmatory laboratory test required to establish the diagnosis.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

A 35-year-old construction worker presents with recurrent severe abdominal cramping, new-onset right foot drop, and a CBC demonstrating microcytic anemia with basophilic stippling.
A 42-year-old agricultural worker complains of progressive stocking-glove sensorimotor neuropathy, painful hyperkeratosis on the palms and soles, and transverse white lines on the fingernails.
A 28-year-old man presents with a new-onset resting tremor, worsening dysarthria, and mildly elevated hepatocellular transaminases without serologic evidence of viral hepatitis.
A 55-year-old man is evaluated for progressive erectile dysfunction, generalized skin hyperpigmentation, and bilateral symmetric arthropathy involving the second and third metacarpophalangeal joints.
A 45-year-old woman receiving long-term total parenteral nutrition develops an erythematous, vesicular perioral and acral dermatitis, accompanied by alopecia and ageusia.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The presentations correspond respectively to lead toxicity, arsenic poisoning, Wilson disease, hereditary hemochromatosis, and zinc deficiency, each requiring a specific targeted laboratory test.
Each clinical presentation contains classic pathognomonic features for a specific condition (lead toxicity, arsenic toxicity, Wilson disease, hemochromatosis, and zinc deficiency), which dictate the precise initial or confirmatory laboratory assay required.

Adım Adım Çözüm

1
Analyze the first clinical vignette for key syndromic features.
Identified abdominal pain, motor neuropathy (foot drop), and basophilic stippling.
These findings are pathognomonic for lead toxicity, necessitating a whole blood lead level rather than a serum level.
2
Evaluate the second clinical vignette for characteristic physical exam findings.
Identified neuropathy, palmoplantar hyperkeratosis, and Mees lines on the nails.
These are hallmark signs of chronic arsenic exposure, best diagnosed via a 24-hour urinary arsenic concentration.
3
Assess the third clinical vignette involving a young adult with mixed neuropsychiatric and hepatic manifestations.
Identified a resting tremor, dysarthria, and unexplained transaminitis.
This combination strongly suggests Wilson disease, which requires testing for serum ceruloplasmin and 24-hour urinary copper.
4
Review the fourth clinical vignette for classic systemic and joint findings.
Identified erectile dysfunction, hyperpigmentation, and second/third metacarpophalangeal arthropathy.
These findings indicate hereditary hemochromatosis, prompting an initial serum iron panel.
5
Analyze the fifth clinical vignette focusing on the nutritional context and cutaneous findings.
Identified a patient on total parenteral nutrition developing periorificial dermatitis and ageusia.
This presentation is characteristic of acquired zinc deficiency, confirmed by measuring the serum zinc level.

Anahtar Kavram

Selecting the most appropriate diagnostic laboratory test requires precise pattern recognition of specific toxicological, metabolic, and nutritional deficiency syndromes, as well as an understanding of the specific specimen type required (e.g., whole blood vs. serum).
Tahmini Süre:2m 0s
Soru 1631Soru →

A 68-year-old institutionalized female with advanced Parkinson disease is evaluated in the emergency department for severe abdominal distension and an inability to pass flatus for the past 48 hours. She has experienced intermittent, crampy abdominal pain and two episodes of nonbilious emesis earlier today. Her medical history is significant for chronic constipation, hypertension, and osteoarthritis. Vital signs show a temperature of 37.2°C (99.0°F), heart rate of 110/min, blood pressure of 132/82 mm Hg, and respiratory rate of 18/min. Physical examination reveals a markedly distended, tympanitic abdomen with high-pitched, 'tinkling' bowel sounds. There is diffuse mild tenderness to palpation but no guarding or rebound tenderness. Digital rectal examination demonstrates an empty rectal vault. An upright abdominal radiograph is obtained, which reveals a massively dilated, comma-shaped large bowel loop originating from the right lower quadrant and projecting toward the left upper quadrant. Multiple dilated loops of small bowel with air-fluid levels are also present, with a complete absence of gas in the distal descending colon and rectum. Based on these imaging findings, which of the following is the most appropriate next step in management?

Cevabı ve açıklamayı göster

Cevap: Emergent surgical exploration and right colectomy

Cevap

Emergent surgical exploration and right colectomy is the most appropriate next step in management.
The correct answer is emergent surgical exploration and right colectomy. The key to this clinical scenario relies entirely on interpreting the exact morphology and vector of the imaging findings. The patient's plain radiograph demonstrates a massively dilated large bowel loop originating from the right lower quadrant (RLQ) and projecting toward the left upper quadrant (LUQ). This specific vector, often referred to as an 'embryo' or 'comma' appearance, is pathognomonic for a cecal volvulus. This contrasts with a sigmoid volvulus, where the dilated loop classically originates in the left lower quadrant (LLQ) and projects toward the right upper quadrant (RUQ) in a 'coffee bean' shape. Because cecal volvulus represents a high-risk closed-loop obstruction with a significant threat of rapid strangulation, and because endoscopic detorsion in the cecum is both technically challenging and associated with a high failure/perforation rate, emergent surgical intervention (e.g., right hemicolectomy) is the definitive standard of care.

Adım Adım Çözüm

1
Interpret the specific orientation of the dilated bowel loop on the abdominal radiograph.
The massively dilated loop originates in the right lower quadrant and projects toward the left upper quadrant, accompanied by small bowel dilation and an empty distal colon.
Differentiating the vector of the dilated loop is critical; a right-to-left vector indicates a cecal volvulus, whereas a left-to-right vector (classic 'coffee bean' sign) indicates a sigmoid volvulus.
2
Correlate the imaging diagnosis with the patient's acute presentation to determine the pathology.
The imaging findings establish a diagnosis of cecal volvulus, which represents a mechanical, closed-loop obstruction.
Closed-loop obstructions carry a rapidly escalating risk of vascular compromise, bowel ischemia, and perforation, necessitating immediate, definitive intervention.
3
Select the appropriate definitive management for the diagnosed condition.
Surgical exploration (typically right colectomy, ileocecectomy, or cecopexy) is selected as the required treatment.
Unlike sigmoid volvulus, which can often be managed initially with endoscopic detorsion, endoscopic management is technically difficult, largely ineffective, and highly hazardous for cecal volvulus, making surgery the standard of care.

Anahtar Kavram

Radiographic differentiation of large bowel volvulus and corresponding management
Soru 1632Soru →

A 47-year-old woman comes to the clinic reporting worsening fatigue, increased thirst, and frequent urination over the past three months. She has a history of chronic cough and was told she had "enlarged lymph nodes" in her chest a year ago, but she did not follow up. Her temperature is 37.0°C (98.6°F), blood pressure is 128/82 mmHg, and pulse is 78/min. Physical examination reveals a few erythematous nodules on her anterior lower legs. Laboratory studies show:

Laboratory ParameterResultReference Range
Calcium, serum12.8 mg/dL8.4-10.2 mg/dL
Phosphorus, serum4.6 mg/dL2.5-4.5 mg/dL
Parathyroid hormone (PTH)9 pg/mL10-65 pg/mL
Creatinine, serum1.1 mg/dL0.6-1.1 mg/dL

Which of the following cellular mechanisms best explains this patient's current laboratory abnormalities?

Cevabı ve açıklamayı göster

Cevap: Unregulated conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D by activated macrophages

Cevap

Unregulated conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D by activated macrophages
The correct answer is the unregulated conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D by activated macrophages. This patient's presentation of hypercalcemia, suppressed parathyroid hormone (PTH), polyuria, and constitutional symptoms, along with a history of bilateral hilar lymphadenopathy and erythema nodosum, is highly suspicious for sarcoidosis. In sarcoidosis and other granulomatous diseases, disease-associated macrophages ectopically express the enzyme 1-alpha-hydroxylase. This enzyme converts 25-hydroxyvitamin D into the active form, 1,25-dihydroxyvitamin D (calcitriol), independent of normal physiologic feedback mechanisms. The excess calcitriol increases intestinal absorption of both calcium and phosphorus, leading to hypercalcemia and normal-to-elevated serum phosphorus. The resultant hypercalcemia suppresses endogenous PTH secretion from the parathyroid glands via negative feedback.

Adım Adım Çözüm

1
Analyze the patient's clinical presentation.
The patient has fatigue, polyuria, a history of bilateral hilar lymphadenopathy, and erythema nodosum.
These findings are classic for sarcoidosis, a systemic granulomatous disease.
2
Interpret the laboratory findings.
The patient has severe hypercalcemia, slightly elevated phosphorus, and a definitively suppressed PTH level.
A suppressed PTH level indicates a PTH-independent mechanism of hypercalcemia, directing the differential diagnosis away from primary hyperparathyroidism.
3
Synthesize clinical and laboratory data to identify the cellular mechanism.
The hypercalcemia is driven by the underlying granulomatous disease process.
Granulomas contain activated macrophages that ectopically express 1-alpha-hydroxylase, which converts 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D, causing increased intestinal absorption of calcium and phosphorus.

Anahtar Kavram

The primary mechanism of hypercalcemia in sarcoidosis and other granulomatous diseases is the unregulated, ectopic production of 1,25-dihydroxyvitamin D (calcitriol) by 1-alpha-hydroxylase expressed in activated macrophages.
Soru 1633Soru →

A 28-year-old woman, gravida 3, para 1, abortus 1, comes to the clinic for a routine prenatal visit at 11 weeks gestation. She has a healthy 3-year-old child and a history of a spontaneous abortion at 10 weeks gestation last year. Over the past 6 months, she has noticed that her fingers frequently turn pale, then blue, and finally red when exposed to cold weather. She also reports intermittent aching in her wrists and knees, but denies any morning stiffness lasting longer than a few minutes. Vital signs are temperature 37.0°C (98.6°F), blood pressure 118/76 mm Hg, pulse 82/min, and respirations 14/min. Physical examination shows no joint swelling, warmth, or erythema. There are no skin rashes, oral ulcers, or alopecia.

Initial laboratory results are as follows:

Hemoglobin: 11.2 g/dL
Leukocyte count: 4,500/mm³
Platelet count: 115,000/mm³
Urinalysis: 1+ protein, no red blood cells or casts

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

Cevabı ve açıklamayı göster

Cevap: Antinuclear antibody and antiphospholipid antibody panel

Cevap

The most appropriate next step is to order an antinuclear antibody and antiphospholipid antibody panel to screen for Systemic Lupus Erythematosus and Antiphospholipid Syndrome.
The correct answer identifies the need for highly sensitive initial screening tests. The patient's constellation of symptoms (Raynaud phenomenon, arthralgias, history of miscarriage, thrombocytopenia, and proteinuria) raises high clinical suspicion for Systemic Lupus Erythematosus (SLE) and secondary Antiphospholipid Syndrome (APS). The most appropriate initial laboratory step is screening with an Antinuclear Antibody (ANA) test, which has excellent sensitivity for SLE. Concurrently, screening for APS with an antiphospholipid antibody panel (lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies) is indicated due to her history of spontaneous abortion and current thrombocytopenia.

Adım Adım Çözüm

1
Analyze the patient's clinical presentation and obstetric history.
The patient exhibits Raynaud phenomenon, arthralgias, a history of a first-trimester spontaneous abortion, mild thrombocytopenia, and proteinuria.
Identifying the syndromic constellation of signs and symptoms is necessary to formulate a prioritized differential diagnosis.
2
Formulate the most likely differential diagnosis.
The combination of findings is highly suggestive of an undiagnosed systemic autoimmune condition, specifically Systemic Lupus Erythematosus (SLE) and secondary Antiphospholipid Syndrome (APS).
SLE frequently presents in women of childbearing age with joint pain, Raynaud's, cytopenias, and renal involvement, while APS is strongly associated with recurrent or unexplained pregnancy loss.
3
Determine the most appropriate initial laboratory evaluation based on the suspected diagnosis.
The initial evaluation requires highly sensitive screening tests: the Antinuclear Antibody (ANA) test for SLE and an antiphospholipid antibody panel for APS.
Highly sensitive tests should be ordered first to efficiently rule out or screen for the condition. Specific confirmatory tests should only follow a positive screening test.

Anahtar Kavram

The initial laboratory evaluation of suspected Systemic Lupus Erythematosus (SLE) requires highly sensitive screening with an Antinuclear Antibody (ANA) test, followed by specific confirmatory testing if positive. Co-evaluation for Antiphospholipid Syndrome (APS) is indicated in patients with a history of pregnancy loss and cytopenias.
Tahmini Süre:1m 15s
Soru 1634Soru →

A 58-year-old man comes to the clinic reporting a two-month history of a persistent left-sided scrotal mass that feels like a 'bag of worms.' The mass does not decrease in size when he lies flat. He also reports intermittent episodes of pink-tinged urine over the past month. His past medical history is significant for a 30-pack-year smoking history, though he quit 5 years ago. His vital signs show a blood pressure of 150/95 mmHg, heart rate 82/min, and a BMI of 28 kg/m2. Physical examination confirms a left-sided varicocele that remains prominent in the supine position. Laboratory testing reveals a hemoglobin of 19.2 g/dL and a hematocrit of 58%. Which of the following best describes the molecular or pathophysiologic mechanism most directly responsible for the laboratory abnormality seen in this patient?

Cevabı ve açıklamayı göster

Cevap: Inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesis

Cevap

Inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesis
The correct answer is inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesis. This patient's presentation of painless gross hematuria and a left-sided varicocele that fails to empty in the supine position is highly suspicious for a left-sided renal cell carcinoma (RCC). The left gonadal vein drains perpendicularly into the left renal vein. An RCC can extend into the renal vein, obstructing the gonadal vein and leading to a left-sided varicocele. Polycythemia (elevated hemoglobin and hematocrit) is a well-documented paraneoplastic syndrome of RCC. This occurs due to the ectopic production of erythropoietin (EPO). At the molecular level, clear cell RCCs are strongly associated with mutations in the von Hippel-Lindau (VHL) tumor suppressor gene. Loss of VHL function prevents the normal ubiquitination and degradation of hypoxia-inducible factor (HIF). The resulting inappropriate stabilization and accumulation of HIF leads to increased transcription of several target genes, including EPO, which causes secondary polycythemia.

Adım Adım Çözüm

1
Analyze the physical exam findings to localize the primary lesion.
The patient has a left-sided varicocele that fails to empty when supine, alongside painless hematuria. This suggests an obstruction of the left renal vein, which the left gonadal vein drains into.
A varicocele that does not decompress raises high suspicion for a left-sided Renal Cell Carcinoma (RCC) invading the renal vein.
2
Evaluate the laboratory abnormalities in the context of the suspected lesion.
The elevated hemoglobin (19.2 g/dL) and hematocrit (58%) indicate polycythemia. In a patient with suspected RCC, this is a recognized paraneoplastic syndrome.
RCC can autonomously secrete hormones, most notably erythropoietin (EPO), causing secondary absolute polycythemia.
3
Determine the molecular mechanism underlying this specific paraneoplastic syndrome.
Ectopic EPO production in clear cell RCC is driven by mutations in the VHL tumor suppressor gene.
Loss of VHL prevents the degradation of hypoxia-inducible factor (HIF), leading to its stabilization and the subsequent autonomous transcription of EPO.

Anahtar Kavram

Renal cell carcinoma (RCC) can present with hematuria and a left-sided varicocele due to left renal vein invasion. It frequently causes paraneoplastic polycythemia due to VHL mutation-mediated stabilization of hypoxia-inducible factor (HIF), leading to autonomous erythropoietin production.
Soru 1635Soru →

Match the following distinct radiographic descriptions with their most likely underlying clinical condition or pathophysiologic diagnosis.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Focal, wedge-shaped enhancement of hepatic segment IV (quadrate lobe) on early arterial phase abdominal CT
Central non-enhancing filling defect within the superior sagittal sinus surrounded by contrast on a head CT venogram
Central focal area of ground-glass opacity completely surrounded by a denser, complete ring of consolidation on high-resolution chest CT
Sharp linear radiopacity traversing the right upper quadrant, distinctly outlined by radiolucent gas on both of its sides on a supine abdominal radiograph

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The correct matching pairs specific imaging findings to their classic underlying diagnoses: Segment IV hepatic enhancement matches Superior Vena Cava Syndrome, the superior sagittal sinus filling defect matches Cerebral Venous Sinus Thrombosis, the ring of consolidation surrounding ground-glass opacity matches Cryptogenic Organizing Pneumonia, and the linear radiopacity outlined by gas matches Pneumoperitoneum.
Each radiographic description corresponds precisely to a classic diagnostic sign. The 'hot quadrate lobe' sign reflects collateral circulation in SVC syndrome. The 'empty delta' sign represents a thrombus in cerebral venous sinus thrombosis. The 'reversed halo' sign is characteristic of cryptogenic organizing pneumonia. The 'falciform ligament' sign indicates free air in pneumoperitoneum on a supine film.

Adım Adım Çözüm

1
Evaluate the focal hepatic segment IV enhancement on arterial CT.
Identified as the 'hot quadrate lobe' sign.
In SVC syndrome, systemic venous return diverts through the internal mammary and paraumbilical veins, directly entering the left portal system and prematurely enhancing segment IV.
2
Evaluate the sagittal sinus filling defect on head CT venogram.
Identified as the 'empty delta' sign.
Pathognomonic for dural venous sinus thrombosis; the 'empty' center represents the thrombus, while the surrounding enhancement is collateral dural venous flow.
3
Evaluate the ring of consolidation around ground-glass opacity on chest CT.
Identified as the 'reversed halo' or 'atoll' sign.
Characteristic of cryptogenic organizing pneumonia (or certain fungal infections), differentiating it from the standard halo sign.
4
Evaluate the linear radiopacity outlined by gas on a supine abdominal X-ray.
Identified as the 'falciform ligament' sign.
Free intraperitoneal air rises in a supine patient, outlining both sides of the falciform ligament, serving as a critical indicator of massive pneumoperitoneum.

Anahtar Kavram

Identification of pathognomonic eponymous imaging signs and understanding their underlying pathophysiologic mechanisms is essential for diagnosing critical vascular, inflammatory, and surgical emergencies.
Soru 1636Soru →

A 9-year-old boy is brought to the emergency department by his parents due to abdominal pain that began yesterday. The pain initially started around his umbilicus but has since migrated to the right lower quadrant. He has had one episode of nonbilious vomiting and has refused to eat since yesterday morning. His temperature is 38.3∘C38.3^\circ\text{C} (101.0∘F101.0^\circ\text{F}), blood pressure is 105/65 mm Hg105/65\text{ mm Hg}, pulse is 110/min110\text{/min}, and respiratory rate is 18/min18\text{/min}. Physical examination reveals localized tenderness halfway between the anterior superior iliac spine and the umbilicus, along with involuntary guarding. Laboratory studies demonstrate a leukocyte count of 14,500/mm314,500/\text{mm}^3 with 82% neutrophils. Which of the following is the most appropriate initial imaging modality to evaluate this patient's condition?

Cevabı ve açıklamayı göster

Cevap: Graded compression ultrasonography of the right lower quadrant

Cevap

Graded compression ultrasonography of the right lower quadrant is the most appropriate initial imaging study.
The correct answer is graded compression ultrasonography. Acute appendicitis classically presents with periumbilical pain migrating to the right lower quadrant, anorexia, nausea, fever, and focal tenderness. In pediatric and pregnant patients, ultrasonography is the initial imaging modality of choice. It is highly specific and avoids the ionizing radiation associated with a CT scan. If the ultrasound appendix cannot be visualized or the results are equivocal, further imaging (such as an MRI or a CT scan with intravenous contrast) may then be performed.

Adım Adım Çözüm

1
Analyze the clinical presentation.
The patient has classic signs of acute appendicitis: migratory periumbilical to right lower quadrant pain, anorexia, fever, focal tenderness at McBurney's point, and leukocytosis with a left shift.
Establishing the most likely diagnosis guides the selection of the appropriate confirmatory test.
2
Consider the patient demographic and associated imaging risks.
The patient is a 9-year-old child. Pediatric patients are highly vulnerable to the long-term oncologic risks associated with ionizing radiation from computed tomography.
Age-specific guidelines mandate minimizing radiation exposure whenever a safer, diagnostically acceptable alternative exists.
3
Determine the optimal imaging sequence.
Graded compression ultrasonography is selected as the initial modality.
Ultrasonography provides a definitive diagnosis in most pediatric cases of appendicitis without radiation exposure. If the ultrasound is nondiagnostic or equivocal, subsequent imaging with CT or MRI can then be justified.

Anahtar Kavram

In pediatric patients with suspected acute appendicitis, graded compression ultrasonography is the initial imaging modality of choice to prevent unnecessary exposure to ionizing radiation.
Soru 1637Soru →

A 62-year-old man comes to the clinic due to a 2-month history of progressive proximal muscle weakness, fatigue, and a 5-kg (11-lb) weight gain. He has a 40-pack-year smoking history. Blood pressure is 168/98 mm Hg, pulse is 88/min, and respirations are 16/min. Physical examination shows central obesity, facial plethora, and violaceous striae over the abdomen. There is 3/5 strength in the proximal muscles of the upper and lower extremities.

Laboratory studies show the following:

TestResultReference Range
Sodium146 mEq/L136-145 mEq/L
Potassium2.6 mEq/L3.5-5.0 mEq/L
Chloride96 mEq/L98-106 mEq/L
Bicarbonate34 mEq/L22-28 mEq/L
Glucose185 mg/dL70-99 mg/dL
Blood urea nitrogen18 mg/dL7-20 mg/dL
Creatinine0.9 mg/dL0.7-1.3 mg/dL

Endocrine studies:

TestResultReference Range
24-hour urine free cortisol850 µg/day10-50 µg/day
Morning serum ACTH240 pg/mL10-60 pg/mL

A high-dose (8 mg) dexamethasone suppression test is performed. The baseline serum cortisol is 42 µg/dL, and the post-dexamethasone serum cortisol is 40 µg/dL.

Which of the following is the most likely diagnosis?

Cevabı ve açıklamayı göster

Cevap: Ectopic ACTH production

Cevap

Ectopic ACTH production
The correct answer is ectopic ACTH production. The patient has clinical signs of Cushing syndrome (weight gain, proximal weakness, striae) and laboratory evidence of severe hypercortisolism (markedly elevated 24-hour urine free cortisol). To determine the etiology of Cushing syndrome, the serum ACTH level is measured. This patient's ACTH is elevated, indicating an ACTH-dependent cause, which narrows the differential to a pituitary adenoma (Cushing disease) or ectopic ACTH production. The high-dose dexamethasone suppression test is then used to differentiate between the two. Ectopic sources of ACTH (such as small cell lung cancer, likely in this heavy smoker) are autonomous and typically do not suppress cortisol production following high-dose dexamethasone administration. In contrast, pituitary adenomas usually retain some negative feedback mechanisms and demonstrate a >50% suppression in cortisol. Furthermore, the patient's severe hypokalemia and metabolic alkalosis are classic for ectopic ACTH production, as massive levels of cortisol overwhelm the renal 11-beta-hydroxysteroid dehydrogenase type 2 enzyme and directly stimulate mineralocorticoid receptors.

Adım Adım Çözüm

1
Identify the presence of hypercortisolism.
Cushing syndrome is confirmed.
The patient has characteristic clinical features and a 24-hour urine free cortisol level of 850 µg/day, which is markedly above the normal reference range.
2
Determine if the hypercortisolism is ACTH-dependent or ACTH-independent.
The hypercortisolism is ACTH-dependent.
The morning serum ACTH level is elevated at 240 pg/mL. A suppressed ACTH would indicate an adrenal or exogenous source.
3
Differentiate between a pituitary and an ectopic source of ACTH using the high-dose dexamethasone suppression test.
The source is ectopic ACTH production.
The serum cortisol did not suppress significantly following high-dose dexamethasone, indicating autonomous ectopic production rather than a pituitary adenoma.

Anahtar Kavram

The high-dose dexamethasone suppression test differentiates between ACTH-dependent causes of Cushing syndrome; pituitary adenomas generally suppress, while ectopic ACTH sources do not.
Tahmini Süre:1m 30s
Soru 1638Soru →

An emergency medical services team brings a 72-year-old man to the emergency department due to severe, escalating lower back pain and urinary retention over the past 14 hours. The patient reports a heavy, numb sensation in his groin and inner thighs, as well as new-onset difficulty ambulating. His medical history includes hypertension, prostate cancer treated with radiation therapy five years ago, and sick sinus syndrome. For the latter, a non-MRI-conditional permanent dual-chamber pacemaker was placed three weeks ago. Vital signs are within normal limits. On physical examination, there is pronounced focal tenderness over the L4-L5 spinous processes. Neurologic assessment shows 4/5 strength in bilateral ankle dorsiflexion and plantar flexion. Sensation to pinprick is diminished in the perianal and perineal regions. Achilles deep tendon reflexes are absent bilaterally. A bedside bladder ultrasound reveals a post-void residual volume of 850 mL. Which of the following is the most appropriate next step in diagnostic imaging for this patient?

Cevabı ve açıklamayı göster

Cevap: Computed tomography myelography

Cevap

Computed tomography myelography
The patient presents with classic red-flag signs of cauda equina syndrome (CES), including severe lower back pain, saddle anesthesia, lower extremity weakness, absent Achilles reflexes, and acute urinary retention (evidenced by a post-void residual volume of 850 mL). This is a surgical emergency that requires prompt imaging to localize the level of nerve root compression, likely due to epidural metastasis from his history of prostate cancer. While magnetic resonance imaging (MRI) is the gold standard for evaluating CES, this patient has an absolute contraindication due to the presence of a recently implanted, non-MRI-conditional pacemaker. In clinical scenarios where MRI cannot be performed, computed tomography (CT) myelography is the most appropriate alternative. This procedure involves the intrathecal administration of contrast followed by a CT scan, providing excellent visualization of the spinal canal, thecal sac, and nerve root compression.

Adım Adım Çözüm

1
Identify the primary clinical syndrome based on the patient's neurologic deficits and autonomic dysfunction.
The combination of severe back pain, saddle anesthesia, lower extremity weakness, absent Achilles reflexes, and acute urinary retention indicates cauda equina syndrome.
Recognizing this neurologic emergency dictates the urgency and type of diagnostic imaging required.
2
Determine the standard imaging modality for the suspected diagnosis.
Magnetic resonance imaging (MRI) of the spine is the gold standard for visualizing thecal sac and nerve root compression.
MRI provides superior soft-tissue contrast without ionizing radiation.
3
Evaluate the patient's medical history for any contraindications to the standard imaging modality.
The patient has a recently implanted, non-MRI-conditional permanent pacemaker, which is an absolute contraindication to undergoing an MRI.
Subjecting this patient to an MRI could lead to device malfunction, lead heating, or fatal arrhythmias.
4
Select the most appropriate alternative imaging modality that provides equivalent diagnostic information.
Computed tomography (CT) myelography is selected.
By injecting contrast into the subarachnoid space prior to the CT scan, this modality effectively outlines the spinal cord and nerve roots, serving as the best alternative when MRI is contraindicated.

Anahtar Kavram

Computed tomography myelography is the imaging modality of choice for suspected cauda equina syndrome or spinal cord compression in patients with absolute contraindications to magnetic resonance imaging.
Soru 1639Soru →

Various hereditary cancer syndromes are characterized by distinct clinical presentations and specific underlying molecular defects. Match each patient's clinical vignette with the fundamental genetic mechanism responsible for their disease pathogenesis.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

A 35-year-old female (BP 185/115 mmHg, HR 105 bpm) is evaluated for a rapidly enlarging thyroid mass. Physical exam notes oral mucosal neuromas. Labs demonstrate elevated serum calcitonin and 24-hour urine fractionated metanephrines.
An asymptomatic 42-year-old male with normal vital signs undergoes endoscopic screening due to family history. Gastroenterology reports the presence of approximately 300 adenomatous colonic polyps.
A 29-year-old female presents with progressive gait ataxia. Vital signs are within normal limits. Neuroimaging identifies a cerebellar hemangioblastoma, while concurrent abdominal ultrasound reveals bilateral renal cysts.
A 48-year-old female discovers a painless, fixed 3-cm breast mass. Vitals are unremarkable. Pathology confirms triple-negative invasive ductal carcinoma. Her pedigree includes a first-degree relative with high-grade serous ovarian cancer.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

MEN2B (vignette 1) is driven by RET receptor tyrosine kinase activation. FAP (vignette 2) is caused by APC mutation and failure to degrade β\beta-catenin. VHL disease (vignette 3) results from impaired HIF-1 α\alpha degradation. HBOC syndrome (vignette 4) is due to defective homologous recombination DNA repair.
This question requires a two-step reasoning process: first, diagnosing the hereditary cancer syndrome from the clinical vignette, and second, identifying the fundamental molecular defect responsible for that syndrome. The vignettes describe MEN2B (RET mutation), FAP (APC mutation), VHL disease (VHL mutation), and HBOC syndrome (BRCA mutation). Matching these clinical phenotypes to their respective receptor tyrosine kinase activation, Wnt/β\beta-catenin signaling dysregulation, impaired HIF-1 α\alpha degradation, and defective homologous recombination correctly maps the neoplastic processes.

Adım Adım Çözüm

1
Analyze the first vignette to diagnose the syndrome and its genetic basis.
The triad of medullary thyroid cancer, pheochromocytoma, and mucosal neuromas diagnoses MEN2B, caused by RET receptor tyrosine kinase activation.
Recognizing the syndromic presentation is the first step to identifying the specific oncogenic driver.
2
Evaluate the second vignette's endoscopic findings.
Hundreds of colonic polyps indicate FAP, which results from APC gene mutation and failure to degrade β\beta-catenin.
FAP has a distinct molecular pathogenesis compared to other polyposis syndromes.
3
Identify the disease described in the third vignette.
Hemangioblastoma and renal cysts are classic for VHL disease, driven by impaired HIF-1 α\alpha degradation.
VHL mutations directly link defective angiogenesis regulation to tumor development.
4
Assess the fourth vignette's family history and pathology.
Triple-negative breast cancer and familial ovarian cancer suggest BRCA mutations, which impair double-strand DNA repair.
BRCA mutations exhibit a characteristic pattern of related malignancies due to genomic instability.

Anahtar Kavram

Molecular pathogenesis and genetic drivers of hereditary cancer syndromes
Soru 1640Soru →

A 24-year-old man is evaluated in the emergency department for severe, escalating right lower leg pain. Twelve hours ago, he sustained a closed mid-shaft tibial fracture during a rugby match and was treated with closed reduction and application of a long-leg cast. He now complains of unrelenting pain that is not relieved by multiple doses of intravenous morphine. The resident physician examines the patient and documents: "The right foot is warm with a capillary refill time of less than 2 seconds. Both the dorsalis pedis and posterior tibial pulses are 2+ and symmetric to the contralateral side. Acute compartment syndrome is highly unlikely given the intact distal perfusion." The resident plans to admit the patient for pain control and observation. Which of the following physical examination findings is the most sensitive and reliable early indicator of the condition the resident erroneously excluded?

Cevabı ve açıklamayı göster

Cevap: Exacerbation of deep pain during passive flexion and extension of the toes

Cevap

Exacerbation of deep pain during passive flexion and extension of the toes
Acute compartment syndrome develops when tissue pressure within a closed fascial space rises above capillary perfusion pressure, leading to microvascular compromise and subsequent muscle and nerve ischemia. The earliest and most sensitive physical examination finding is severe pain out of proportion to the apparent injury, which is classically exacerbated by passively stretching the ischemic muscles contained within the affected compartment (e.g., passive plantarflexion/dorsiflexion of the toes). The resident's conclusion is a common and dangerous pitfall; because fascial compartment pressure rarely exceeds systolic blood pressure, major arterial flow continues, meaning distal pulses and capillary refill almost always remain normal during the early, salvageable stages of the syndrome.

Adım Adım Çözüm

1
Analyze the clinical vignette
Patient has a recent tibial fracture with cast placement, presenting with pain out of proportion to the injury that is unresponsive to opioids.
This is the classic presentation of acute compartment syndrome, a surgical emergency.
2
Evaluate the resident's physical exam findings and conclusion
The resident ruled out compartment syndrome because distal pulses (dorsalis pedis, posterior tibial) are intact and capillary refill is normal.
This represents a critical misunderstanding of the pathophysiology. Compartment syndrome occurs when interstitial pressure exceeds capillary perfusion pressure (typically around 30 mm Hg), not systolic arterial pressure (120 mm Hg).
3
Identify the most sensitive early clinical sign of compartment syndrome
Pain on passive stretching of the muscles within the affected compartment (e.g., moving the toes to stretch the anterior/deep posterior compartments) is the earliest and most reliable physical examination finding.
Ischemic muscle is highly sensitive to stretch, providing a clinical signal long before large-vessel occlusion (loss of pulses) or irreversible nerve damage (loss of two-point discrimination) occurs.

Anahtar Kavram

In acute compartment syndrome, large arterial pulses typically remain intact because compartmental pressures exceed capillary closing pressure but do not reach systolic arterial pressure. Pain on passive stretch is the most sensitive early clinical sign.
ÖncekiSayfa 82 / 237Sonraki
Tüm alıştırma soruları — USMLE Step 3 | Examkin