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Internal Medicine

3151 questions

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Question 1721Question →

A 48-year-old man comes to the clinic reporting progressive fatigue, decreased libido, and constant cold intolerance over the past six months. He also mentions occasionally bumping into objects on his far right and left sides. Vital signs are within normal limits, though his heart rate is 54/min. Physical examination reveals delayed relaxation of deep tendon reflexes and a visual field deficit in the outer half of both eyes. Laboratory testing shows:

TestResultReference Range
Thyroid-stimulating hormone (TSH)1.2 mU/L0.4 - 4.0 mU/L
Free T40.4 ng/dL0.9 - 1.7 ng/dL

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

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Answer: Magnetic resonance imaging of the brain

Answer

Magnetic resonance imaging of the brain
This patient presents with signs and symptoms of hypothyroidism (fatigue, cold intolerance, bradycardia, and delayed deep tendon reflexes) combined with decreased libido and bitemporal hemianopsia. The laboratory findings of a low free T4 paired with an inappropriately normal TSH confirm the diagnosis of central (secondary) hypothyroidism. The visual field deficit indicates a mass lesion in the sella turcica that is extending superiorly and compressing the optic chiasm. The most likely etiology is a pituitary macroadenoma (such as a non-functioning adenoma or a prolactinoma). The most appropriate next step in evaluation is an MRI of the brain to characterize the mass before planning surgical or medical intervention.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient has symptoms of hypothyroidism (fatigue, cold intolerance, bradycardia, delayed reflexes) alongside bitemporal hemianopsia (loss of outer visual fields).
Identifying the clinical syndrome guides the interpretation of the laboratory data.
2
Interpret the thyroid function tests.
Free T4 is low, but TSH is inappropriately normal (1.2 mU/L), which points to a central (pituitary or hypothalamic) etiology rather than a primary thyroid gland failure.
In primary hypothyroidism, a low T4 would trigger a compensatory elevation in TSH. A normal or low TSH with a low T4 is the hallmark of central hypothyroidism.
3
Synthesize findings to determine the next best step.
The combination of central hypothyroidism and optic chiasm compression strongly suggests a large pituitary mass (macroadenoma). Therefore, brain imaging is required.
MRI of the brain is the gold standard for visualizing the sella turcica and evaluating for pituitary tumors.

Key Concept

Patients with a low free T4 and an inappropriately normal or low TSH have central hypothyroidism, which necessitates an MRI of the brain to evaluate for a pituitary mass, especially when accompanied by compressive symptoms like bitemporal hemianopsia.
Question 1722Question →

A 62-year-old man is evaluated in the hospital for decreased urine output over the past 24 hours. He was admitted three days ago for the treatment of community-acquired pneumonia with intravenous antibiotics. His blood pressure is 110/70 mm Hg and his pulse is 88/min. Laboratory studies show:

Serum sodium: 140 mEq/L140 \text{ mEq/L}
Serum creatinine: 4.0 mg/dL4.0 \text{ mg/dL}
Urine sodium: 70 mEq/L70 \text{ mEq/L}
Urine creatinine: 80 mg/dL80 \text{ mg/dL}

Based on these laboratory values, what is this patient's fractional excretion of sodium (in percent)?

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Answer: 2.5

Answer

2.5
The correct calculation for the Fractional Excretion of Sodium (FENa) uses the formula (UNa×PCr)/(PNa×UCr)×100(U_{Na} \times P_{Cr}) / (P_{Na} \times U_{Cr}) \times 100. Plugging in the given values gives (70×4.0)/(140×80)×100=280/11200×100=2.5%(70 \times 4.0) / (140 \times 80) \times 100 = 280 / 11200 \times 100 = 2.5\%. A FENa greater than 2% in the setting of acute kidney injury is typically suggestive of acute tubular necrosis (ATN), which aligns with this patient's recent exposure to nephrotoxic intravenous antibiotics.

Step-by-Step Solution

1
Identify the mathematical formula for Fractional Excretion of Sodium (FENa).
FENa=UNa×PCrPNa×UCr×100 FENa = \frac{U_{Na} \times P_{Cr}}{P_{Na} \times U_{Cr}} \times 100
This formula relates the clearance of sodium to the clearance of creatinine to determine the percentage of filtered sodium that is excreted.
2
Substitute the patient's laboratory values into the FENa formula.
FENa=70×4.0140×80×100 FENa = \frac{70 \times 4.0}{140 \times 80} \times 100
Applying the specific serum and urine values provided in the clinical vignette.
3
Perform the calculation to find the final percentage.
FENa=28011200×100=0.025×100=2.5 FENa = \frac{280}{11200} \times 100 = 0.025 \times 100 = 2.5
Calculating the expression yields the final FENa percentage.

Key Concept

The Fractional Excretion of Sodium (FENa) is a calculated metric used to evaluate acute kidney injury, differentiating between prerenal (FENa < 1%) and intrinsic renal (FENa > 2%) etiologies.
Question 1723Question →

A 63-year-old man is brought to the emergency department by ambulance after vomiting a large amount of bright red blood. He has a history of alcohol use disorder and cirrhosis. On arrival, he is confused and lethargic. Temperature is 36.5°C (97.7°F), blood pressure is 85/50 mm Hg, and pulse is 124/min. Physical examination shows scleral icterus, spider angiomas on the chest, and a distended abdomen with a positive fluid wave. Two large-bore intravenous lines are placed, and fluid resuscitation is initiated.

Laboratory studies obtained prior to fluid administration show:

Serum:
Sodium: 140 mEq/L
Blood urea nitrogen: 68 mg/dL
Creatinine: 2.1 mg/dL

Urine:
Sodium: 12 mEq/L
Creatinine: 60 mg/dL

Calculate the patient's fractional excretion of sodium (in percent).

Show answer & explanation

Answer: 0.3

Answer

0.3
The fractional excretion of sodium (FENa) is a useful calculation to distinguish prerenal acute kidney injury from intrinsic renal causes, such as acute tubular necrosis. A FENa of less than 1% typically indicates a prerenal state (e.g., hypovolemia or decreased effective circulating volume), where the kidneys appropriately and avidly reabsorb sodium to restore volume. In this patient with upper gastrointestinal bleeding and severe hypovolemia, the calculated FENa is 0.3%0.3\%, which strongly supports a prerenal etiology for his acute renal impairment.

Step-by-Step Solution

1
Identify the required variables for the FENa formula from the laboratory results.
UNaU_{Na} = 12 mEq/L, PCrP_{Cr} = 2.1 mg/dL, PNaP_{Na} = 140 mEq/L, UCrU_{Cr} = 60 mg/dL.
These specific serum and urine values are necessary to calculate the fractional excretion of sodium.
2
Set up the FENa formula.
FENa=UNa×PCrPNa×UCr×100FENa = \frac{U_{Na} \times P_{Cr}}{P_{Na} \times U_{Cr}} \times 100
This formula evaluates sodium clearance relative to creatinine clearance to estimate the percentage of filtered sodium that is excreted.
3
Perform the calculation.
FENa=12×2.1140×60×100=25.28400×100=0.003×100=0.3FENa = \frac{12 \times 2.1}{140 \times 60} \times 100 = \frac{25.2}{8400} \times 100 = 0.003 \times 100 = 0.3
Mathematically solving the equation yields the final percentage.

Key Concept

Fractional Excretion of Sodium (FENa) Calculation
Question 1724Question →

A 6868-year-old woman is evaluated in the hospital for severe shortness of breath. She has a history of diffuse large B-cell lymphoma and chronic obstructive pulmonary disease. Two days ago, she underwent uncomplicated placement of a right internal jugular venous port. Today, she was admitted for symptomatic anemia and was prescribed two units of packed red blood cells. Toward the end of the second unit's infusion, she acutely developed dyspnea, orthopnea, and a cough productive of pink, frothy sputum.

Her temperature is 37.6∘C37.6^\circ\text{C} (99.7∘F99.7^\circ\text{F}), blood pressure is 178/92 mmHg178/92\text{ mmHg}, pulse is 112/min112/\text{min}, and respirations are 28/min28/\text{min}. Pulse oximetry shows 88%88\% on room air.

Physical examination reveals elevated jugular venous pressure. The port site is clean and without erythema. Cardiopulmonary auscultation reveals an S3 gallop, bilateral basilar crackles, and scattered expiratory wheezes.

Laboratory studies show:
Hemoglobin: 8.9 g/dL8.9\text{ g/dL} (up from 6.8 g/dL6.8\text{ g/dL} before transfusion)
Leukocyte count: 8,400/mm38,400/\text{mm}^3
Platelet count: 145,000/mm3145,000/\text{mm}^3
Brain natriuretic peptide (BNP): 850 pg/mL850\text{ pg/mL}
Creatinine: 1.1 mg/dL1.1\text{ mg/dL}

Which of the following is the most appropriate next step in management?

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Answer: Discontinue the transfusion and administer intravenous furosemide

Answer

The most appropriate next step is to stop the transfusion and administer intravenous furosemide to manage the volume overload.
This patient is experiencing Transfusion-Associated Circulatory Overload (TACO), a known complication of blood product administration, particularly in older patients or those with underlying cardiopulmonary disease. The rapid expansion of intravascular volume leads to acute decompensated heart failure and cardiogenic pulmonary edema. Classic signs include severe respiratory distress, hypertension, tachycardia, elevated jugular venous pressure (JVP), an S3 gallop, and bilateral pulmonary crackles. Laboratory testing often reveals an elevated BNP. The most appropriate next step in management is to immediately discontinue the transfusion to prevent further volume expansion, provide supplemental oxygen, and administer intravenous loop diuretics (e.g., furosemide) to reduce intravascular volume.

Step-by-Step Solution

1
Analyze the patient's acute symptoms and physical exam findings during a blood transfusion.
The patient developed acute dyspnea, hypertension, hypoxia, JVD, crackles, and an S3 gallop.
Identifying the constellation of symptoms helps differentiate between various transfusion reactions.
2
Differentiate between TRALI (Transfusion-Related Acute Lung Injury) and TACO (Transfusion-Associated Circulatory Overload).
The presence of hypertension, JVD, an S3 gallop, and markedly elevated BNP confirms TACO. TRALI typically presents with hypotension and normal cardiac filling pressures.
TRALI and TACO are the two most common causes of severe respiratory distress following transfusion, but their treatments differ significantly.
3
Determine the best management step for TACO.
The correct management is immediate cessation of the transfusion, respiratory support (oxygen), and diuresis (intravenous furosemide).
TACO is a form of acute decompensated heart failure; reducing intravascular volume is essential for recovery.

Key Concept

Transfusion-Associated Circulatory Overload (TACO)
Question 1725Question →

A 52-year-old man is evaluated for progressive central adiposity, severe fatigue, new-onset hypertension, and proximal muscle weakness. Physical examination reveals facial plethora, supraclavicular fat pads, and thin skin with easy bruising. He takes no medications. Arrange the following diagnostic steps in the most appropriate chronological sequence to definitively diagnose and localize his condition, assuming standard endocrine algorithms are followed and the results of each step sequentially lead to the diagnosis of an occult ectopic ACTH-secreting tumor.

Drag items to arrange them in the correct order

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Answer

The correct sequence is: 1) 24-hour urine free cortisol, 2) Plasma ACTH concentration, 3) Pituitary MRI, 4) Inferior petrosal sinus sampling (IPSS), 5) CT scan of the chest and abdomen.
The standard diagnostic algorithm for Cushing syndrome dictates a strict sequence to avoid misdiagnosis due to incidentalomas. Hypercortisolism must first be confirmed (24-hour urine free cortisol). Next, ACTH dependence is established (plasma ACTH). If ACTH-dependent, pituitary MRI is performed. Because up to 10% of the normal population has incidental non-functioning pituitary microadenomas, and because ACTH-secreting adenomas can be completely occult on MRI, a negative or equivocal (<6 mm) MRI mandates bilateral inferior petrosal sinus sampling (IPSS). Only after IPSS confirms the absence of a central ACTH gradient (indicating an ectopic source) should chest/abdominal imaging be performed to locate the ectopic tumor.

Step-by-Step Solution

1
Establish hypercortisolism
Elevated 24-hour urine free cortisol
To confirm pathological hypercortisolism before localizing the source.
2
Determine ACTH dependence
Elevated or inappropriately normal plasma ACTH
To differentiate ACTH-dependent from ACTH-independent (adrenal) causes.
3
Localize ACTH source initially
Negative or equivocal pituitary MRI
Pituitary adenoma is the most common cause; MRI is the first-line imaging modality.
4
Differentiate pituitary vs ectopic biochemically
No central-to-peripheral ACTH gradient on IPSS
Required when MRI is negative to definitively prove an ectopic source.
5
Localize ectopic source
Identification of a tumor (e.g., bronchial carcinoid) on CT chest/abdomen
Performed only after biochemical confirmation of ectopic ACTH production.

Key Concept

The diagnostic algorithm for Cushing syndrome requires sequential biochemical confirmation of hypercortisolism, determination of ACTH dependence, and specific localization tests (MRI followed by IPSS if necessary) before searching for an ectopic source.
Question 1726Question →

Match each clinical laboratory profile concerning calcium homeostasis to the most likely underlying pathophysiologic diagnosis.

Click a left item, then click its matching right item

Items

Hypercalcemia, elevated parathyroid hormone (PTH), hypophosphatemia, and hypercalciuria
Hypercalcemia, normal to mildly elevated PTH, and marked hypocalciuria (urine calcium to creatinine clearance ratio < 0.01)
Hypocalcemia, inappropriately low PTH, and hyperphosphatemia
Hypocalcemia, elevated PTH, hypophosphatemia, and elevated alkaline phosphatase
Hypercalcemia, suppressed PTH, hypophosphatemia, and elevated PTH-related peptide (PTHrP)

Matches

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Answer

The accurate diagnoses correspond to distinct biochemical signatures: Primary hyperparathyroidism with hypercalciuria, FHH with marked hypocalciuria, Primary hypoparathyroidism with low PTH and hyperphosphatemia, Severe vitamin D deficiency with secondary hyperparathyroidism and elevated alkaline phosphatase, and Malignancy with suppressed endogenous PTH.
Each laboratory pattern uniquely identifies a defect in the calcium homeostasis axis. Primary hyperparathyroidism and FHH are differentiated by urine calcium excretion. Hypoparathyroidism lacks the PTH hormone entirely, while vitamin D deficiency induces a secondary hyperparathyroidism to maintain calcium at the expense of phosphate and bone. Malignancy mimics PTH action via PTHrP, raising calcium but appropriately suppressing endogenous PTH.

Step-by-Step Solution

1
Analyze the relationship between serum calcium and PTH levels.
Hypercalcemia with unsuppressed PTH indicates a primary parathyroid disorder or CaSR defect. Hypercalcemia with suppressed PTH indicates an exogenous source or malignancy. Hypocalcemia with low PTH indicates parathyroid failure. Hypocalcemia with high PTH indicates an appropriate physiologic response to calcium loss or malabsorption.
The direction of the PTH response distinguishes primary parathyroid disorders from secondary responses to deranged calcium homeostasis.
2
Differentiate the hypercalcemic states with unsuppressed PTH by evaluating urinary calcium.
Hypercalciuria points to primary hyperparathyroidism, whereas pronounced hypocalciuria points to familial hypocalciuric hypercalcemia (FHH).
FHH involves a mutated calcium-sensing receptor that intrinsically increases renal calcium reabsorption, whereas primary hyperparathyroidism increases the total filtered load of calcium, spilling it into the urine.
3
Differentiate the hypocalcemic states based on phosphate and alkaline phosphatase.
Inappropriately low PTH with hyperphosphatemia confirms primary hypoparathyroidism. Elevated PTH with hypophosphatemia and elevated alkaline phosphatase confirms secondary hyperparathyroidism, typically due to severe vitamin D deficiency.
Vitamin D deficiency causes malabsorption of calcium, triggering compensatory PTH elevation which normalizes calcium through bone turnover but worsens phosphate wasting.

Key Concept

Calcium Homeostasis and Parathyroid Disorders
Question 1727Question →

During a preoperative assessment, a 74-year-old male is reviewed by the surgical team three days before an elective left total hip arthroplasty. He has longstanding osteoarthritis, diet-controlled type 2 diabetes mellitus, and mild benign prostatic hyperplasia. The patient feels well and explicitly denies any current urinary urgency, dysuria, increased frequency, or flank discomfort. His temperature is 37.0°C (98.6°F), blood pressure is 132/84 mmHg, and heart rate is 76/min. Aside from left hip stiffness and an antalgic gait, the physical examination is unremarkable.

Laboratory investigations are obtained as part of standard preoperative protocols. A midstream urine sample shows 18 leukocytes/hpf, positive leukocyte esterase, and negative nitrites. A reflex urine culture subsequently isolates >105>10^5 CFU/mL of Extended-Spectrum Beta-Lactamase (ESBL)-producing *Escherichia coli*. The isolate is resistant to ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole, but retains susceptibility to meropenem, nitrofurantoin, and fosfomycin.

Based on these findings, which of the following is the most appropriate next step in the management of this patient's urinary findings?

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Answer: Proceed with the scheduled surgery without targeted urinary antimicrobial therapy

Answer

The most appropriate action is to proceed with the scheduled surgery without targeted urinary antimicrobial therapy.
The correct course of action is to proceed with the scheduled hip arthroplasty without prescribing targeted antibiotics for the urine. This patient's presentation meets the criteria for asymptomatic bacteriuria (ASB): bacterial growth of >105>10^5 CFU/mL in the absence of localized or systemic symptoms of a urinary tract infection. The Infectious Diseases Society of America (IDSA) explicitly recommends against screening for or treating ASB in patients undergoing non-urologic surgeries, including orthopedic joint replacements. Numerous large cohort studies have demonstrated that preoperative ASB is not a significant risk factor for prosthetic joint infection, and eradicating the bacteriuria prior to surgery does not improve surgical outcomes. While the presence of an ESBL-producing organism might seem alarming, treating colonization only exposes the patient to adverse drug effects, increases the risk of *Clostridioides difficile* infection, and promotes further antimicrobial resistance. Pyuria frequently accompanies ASB in older adults and is not an independent indication for treatment.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and laboratory results.
The patient has >105>10^5 CFU/mL of ESBL-producing E. coli and pyuria, but entirely lacks signs or symptoms of a urinary tract infection (no dysuria, urgency, or fever).
Differentiating between asymptomatic bacteriuria (ASB) and a symptomatic UTI is the foundational step in urinary diagnostics.
2
Determine the significance of pyuria in this context.
Pyuria (18 leukocytes/hpf) is recognized as a common accompanying finding in ASB, particularly in the elderly, and does not alter the diagnosis.
Many clinicians erroneously believe pyuria mandates treatment; it is an expected inflammatory response to colonization.
3
Apply current treatment guidelines for ASB in the setting of upcoming surgery.
Guidelines strictly advise against treating ASB prior to non-urologic surgeries, including orthopedic joint replacements.
Treatment does not reduce the risk of prosthetic joint infections and unnecessarily drives antibiotic resistance.

Key Concept

Asymptomatic bacteriuria (ASB) does not require treatment prior to non-urologic surgeries, such as orthopedic joint arthroplasty, regardless of the organism's antimicrobial resistance profile or the presence of pyuria.
Question 1728Question →

Match each clinical presentation and associated laboratory profile to the most likely underlying pathophysiologic mechanism.

Click a left item, then click its matching right item

Items

A 42-year-old woman with recurrent calcium phosphate kidney stones. Labs show Na+Na^+ 140140 mEq/L, K+K^+ 2.72.7 mEq/L, Cl−Cl^- 115115 mEq/L, HCO3−HCO_3^- 1313 mEq/L. Urine studies reveal pH 6.86.8, Na+Na^+ 4545 mEq/L, K+K^+ 2020 mEq/L, Cl−Cl^- 3535 mEq/L.
A 58-year-old man with long-standing type 2 diabetes mellitus. Labs show Na+Na^+ 138138 mEq/L, K+K^+ 5.65.6 mEq/L, Cl−Cl^- 110110 mEq/L, HCO3−HCO_3^- 1616 mEq/L. Urine studies reveal pH 5.25.2, Na+Na^+ 5050 mEq/L, K+K^+ 2525 mEq/L, Cl−Cl^- 6565 mEq/L.
A 24-year-old woman evaluated for episodic severe muscle weakness. Labs show Na+Na^+ 136136 mEq/L, K+K^+ 2.92.9 mEq/L, Cl−Cl^- 114114 mEq/L, HCO3−HCO_3^- 1212 mEq/L. Urine studies reveal pH 5.05.0, Na+Na^+ 3030 mEq/L, K+K^+ 1515 mEq/L, Cl−Cl^- 7575 mEq/L.
A 32-year-old woman with lethargy, poor dentition, and muscle cramps. Labs show Na+Na^+ 139139 mEq/L, K+K^+ 2.42.4 mEq/L, Cl−Cl^- 9292 mEq/L, HCO3−HCO_3^- 3535 mEq/L. Urine studies reveal pH 7.27.2, Na+Na^+ 4040 mEq/L, K+K^+ 3535 mEq/L, Cl−Cl^- 88 mEq/L.

Matches

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Answer

Patient 1 matches impaired distal tubular secretion of hydrogen ions (Type 1 RTA). Patient 2 matches decreased production or effect of aldosterone (Type 4 RTA). Patient 3 matches profound gastrointestinal bicarbonate loss. Patient 4 matches gastric volume and hydrochloric acid depletion.
Each laboratory profile requires multi-step analysis: calculating the serum anion gap and, if normal, calculating the urine anion gap (UAG=Na++K+−Cl−\text{UAG} = Na^+ + K^+ - Cl^-). A negative UAG indicates intact renal ammonium excretion (e.g., gastrointestinal bicarbonate loss), whereas a positive UAG indicates impaired renal acidification (e.g., renal tubular acidosis). The profiles are further differentiated by serum potassium levels and urine pH. For metabolic alkalosis, the urine chloride level successfully differentiates saline-responsive from saline-resistant forms.

Step-by-Step Solution

1
Calculate the serum anion gap for each acid-base disturbance using the formula AG=Na+−(Cl−+HCO3−)\text{AG} = Na^+ - (Cl^- + HCO_3^-).
Patients 1, 2, and 3 have a normal serum anion gap (between 10−1210-12 mEq/L), identifying normal anion gap metabolic acidosis (NAGMA). Patient 4 has metabolic alkalosis (HCO3−HCO_3^- of 3535 mEq/L).
Differentiates between high anion gap metabolic acidosis (HAGMA), NAGMA, and metabolic alkalosis to establish the primary disorder.
2
For patients with NAGMA (1, 2, and 3), calculate the urine anion gap using the formula UAG=Na++K+−Cl−\text{UAG} = Na^+ + K^+ - Cl^-.
Patient 1: UAG=45+20−35=+30\text{UAG} = 45 + 20 - 35 = +30. Patient 2: UAG=50+25−65=+10\text{UAG} = 50 + 25 - 65 = +10. Patient 3: UAG=30+15−75=−30\text{UAG} = 30 + 15 - 75 = -30.
A negative UAG indicates appropriate renal ammonium excretion (e.g., GI loss of HCO3−HCO_3^-), while a positive UAG indicates impaired renal acid excretion (e.g., Renal Tubular Acidosis).
3
Evaluate serum potassium and urine pH for patients with positive UAG to differentiate RTA types.
Patient 1 has hypokalemia and a urine pH > 5.55.5, indicating Type 1 RTA. Patient 2 has hyperkalemia and a urine pH < 5.55.5, indicating Type 4 RTA.
Type 1 RTA involves a distal H+H^+ secretion defect (high urine pH, hypokalemia). Type 4 involves aldosterone deficiency or resistance (low urine pH, hyperkalemia).
4
Evaluate the metabolic alkalosis in Patient 4 using the urine chloride level.
Patient 4 has a urine chloride of 88 mEq/L (which is < 2020 mEq/L).
Low urine chloride signifies a chloride-responsive metabolic alkalosis, commonly due to gastric fluid loss (vomiting), supporting the clinical clues of lethargy and poor dentition.

Key Concept

Differentiation of normal anion gap metabolic acidosis (NAGMA) using the urine anion gap, serum potassium, and urine pH, alongside identifying chloride-responsive metabolic alkalosis via urine chloride levels.
Question 1729Question →

Match the following serum laboratory profiles with the most likely underlying pathophysiologic diagnosis.

Click a left item, then click its matching right item

Items

High Calcium, High Parathyroid Hormone (PTH)
High Calcium, Low Parathyroid Hormone (PTH)
Low Calcium, High Parathyroid Hormone (PTH)
Low Calcium, Low Parathyroid Hormone (PTH)

Matches

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Answer

High Calcium and High PTH match Primary hyperparathyroidism. High Calcium and Low PTH match Hypercalcemia of malignancy. Low Calcium and High PTH match Secondary hyperparathyroidism. Low Calcium and Low PTH match Primary hypoparathyroidism.
Understanding the negative feedback loop between calcium and PTH is essential for solving this. High calcium should physiologically suppress PTH. If it does not, the parathyroid gland is autonomously secreting PTH (primary hyperparathyroidism). If high calcium suppresses PTH appropriately, the calcium is originating from another source (e.g., malignancy). Low calcium should stimulate PTH (secondary hyperparathyroidism). If PTH is inappropriately low despite low calcium, the parathyroid gland has failed (hypoparathyroidism).

Step-by-Step Solution

1
Evaluate the serum calcium level to determine if the patient has hypercalcemia or hypocalcemia.
Categorizes the patient into a high or low calcium state.
Calcium is the tightly regulated end-product in this feedback loop, and its level guides the initial differential diagnosis.
2
Evaluate the parathyroid hormone (PTH) level in the context of the identified calcium level.
Determines whether the PTH level is appropriate (physiologic response) or inappropriate (pathologic source) for the calcium state.
An intact physiological axis should suppress PTH when calcium is high, and increase PTH when calcium is low. Deviations indicate primary parathyroid pathology.
3
Correlate the specific pattern to the correct etiology.
High/High indicates primary hyperparathyroidism; High/Low indicates an independent calcium source suppressing normal glands; Low/High indicates normal parathyroid response to external hypocalcemia; Low/Low indicates parathyroid failure.
This finalizes the diagnosis based on the established rules of the calcium-PTH feedback loop.

Key Concept

The negative feedback loop between serum calcium and parathyroid hormone (PTH) in diagnosing disorders of calcium metabolism.
Question 1730Question →

A 62-year-old woman visits the urgent care center complaining of severe difficulty breathing that started three days ago. She states that she has developed a dry, hacking cough and finds herself unable to sleep unless she is sitting upright in her recliner. Her medical history is significant for long-standing hypertension, type 2 diabetes mellitus, and a 35-pack-year smoking habit. She currently takes amlodipine, metformin, and daily low-dose aspirin. Her temperature is 37.1°C (98.8°F), blood pressure is 178/98 mmHg, pulse is 114/min, and respiratory rate is 26/min. Oxygen saturation is 89% on room air. Physical examination reveals distended neck veins while sitting at a 45-degree incline. Auscultation of the lungs reveals bilateral expiratory wheezes and fine inspiratory crackles at both lung bases. Cardiac auscultation demonstrates a regular tachycardia with a distinct S4 gallop. Which of the following is the most appropriate initial management for this patient's current condition?

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Answer: Intravenous administration of a loop diuretic

Answer

Intravenous administration of a loop diuretic is the correct intervention, as the presentation is consistent with acute decompensated heart failure requiring immediate preload reduction.
The patient's acute dyspnea, extreme orthopnea, elevated jugular venous pressure, S4 gallop, and bibasilar crackles with wheezing represent acute decompensated heart failure (ADHF) with pulmonary edema. In patients with severe hypertension and ADHF, immediate intervention with intravenous loop diuretics is the standard of care to rapidly reduce intravascular volume and left ventricular preload, thereby relieving pulmonary congestion.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and vital signs.
The patient has acute dyspnea, orthopnea (sleeping in a recliner), hypoxia (89% on room air), hypertension, and tachycardia.
Identifying the acuity and nature of the respiratory distress is critical to distinguishing between cardiac, pulmonary, and systemic etiologies.
2
Interpret the physical examination findings.
Elevated jugular venous pressure, an S4 gallop, bibasilar crackles, and wheezing are present.
An S4 gallop (indicating a stiff, non-compliant left ventricle) and JVD (indicating right-sided fluid overload) strongly point toward acute decompensated heart failure. The wheezing represents 'cardiac asthma' caused by peribronchial edema.
3
Determine the most appropriate immediate management.
Intravenous loop diuretics (such as furosemide) are indicated.
The primary mechanism of respiratory failure here is pulmonary edema due to left ventricular failure and volume overload. IV loop diuretics rapidly reduce preload and pulmonary congestion, improving oxygenation.

Key Concept

Patients with acute decompensated heart failure can present with wheezing ('cardiac asthma') due to peribronchial edema. The presence of JVD, orthopnea, and an S3 or S4 gallop helps differentiate it from a COPD exacerbation, and immediate management requires intravenous loop diuretics.
Question 1731Question →

A 55-year-old woman comes to the clinic for a routine health maintenance examination. She reports mild fatigue over the last few months but attributes it to her busy work schedule. She denies any weight changes, cold intolerance, constipation, or changes in her skin and hair. Her medical history is unremarkable, and she takes no medications. Vital signs are within normal limits. Physical examination reveals a normal-appearing, non-tender thyroid gland with no palpable nodules. Laboratory studies show:

Serum thyroid-stimulating hormone (TSH): 8.5 μU/mL8.5 \text{ } \mu\text{U/mL} (Normal: 0.4−4.0 μU/mL0.4 - 4.0 \text{ } \mu\text{U/mL})
Serum free thyroxine (T4): 1.3 ng/dL1.3 \text{ ng/dL} (Normal: 0.9−1.7 ng/dL0.9 - 1.7 \text{ ng/dL})

Which of the following is the most likely diagnosis?

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Answer: Subclinical hypothyroidism

Answer

Subclinical hypothyroidism
The correct diagnosis is subclinical hypothyroidism. This condition is defined biochemically by an elevated serum TSH concentration in the setting of normal serum free T4 and T3 concentrations. Patients are typically asymptomatic, though some may report mild, non-specific symptoms such as fatigue. In contrast, overt hypothyroidism requires a low free T4 level.

Step-by-Step Solution

1
Evaluate the patient's symptoms and clinical context.
The patient is generally healthy and asymptomatic aside from mild fatigue.
Establishing the clinical status helps differentiate overt thyroid disease from subclinical or alternative diagnoses.
2
Interpret the serum TSH level.
TSH is elevated at 8.5 μU/mL.
An elevated TSH indicates that the pituitary gland is attempting to stimulate the thyroid, typically because thyroid hormone levels are insufficient.
3
Interpret the serum free T4 level.
Free T4 is normal at 1.3 ng/dL.
The free T4 level determines whether the hypothyroidism is overt (low free T4) or subclinical (normal free T4).
4
Synthesize the findings to make a diagnosis.
The combination of elevated TSH and normal free T4 points strictly to subclinical hypothyroidism.
This specific laboratory pattern defines subclinical hypothyroidism, regardless of the presence of mild non-specific symptoms like fatigue.

Key Concept

Diagnosis of subclinical hypothyroidism
Estimated Time:45s
Question 1732Question →

Match each of the following hypothalamic-pituitary-adrenal axis laboratory profiles with the most likely underlying pathophysiologic diagnosis.

Click a left item, then click its matching right item

Items

Elevated baseline serum cortisol, elevated ACTH, and cortisol suppression >50% following high-dose dexamethasone administration.
Elevated baseline serum cortisol, elevated ACTH, and lack of cortisol suppression following high-dose dexamethasone administration.
Elevated baseline serum cortisol, suppressed ACTH, and lack of cortisol suppression following high-dose dexamethasone administration.
Low morning serum cortisol, elevated ACTH, hyponatremia, and hyperkalemia.
Low morning serum cortisol, decreased ACTH, hyponatremia, and normokalemia.

Matches

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Answer

The correct matches rely on identifying ACTH dependence, the presence of negative feedback in high-dose dexamethasone testing, and the integrity of the mineralocorticoid axis via serum potassium levels.
The correct pairings successfully utilize the principles of physiologic negative feedback mechanisms. Cortisol suppresses ACTH; pituitary adenomas retain partial sensitivity to this feedback (high-dose dexamethasone suppression), ectopic tumors do not. Furthermore, the renin-angiotensin-aldosterone axis operates independently of ACTH, distinguishing primary from secondary insufficiency via potassium levels.

Step-by-Step Solution

1
Evaluate hypercortisolism profiles based on ACTH levels to determine the source.
Suppressed ACTH indicates an ACTH-independent primary adrenal source. Elevated ACTH indicates an ACTH-dependent source (pituitary or ectopic).
Cortisol exerts negative feedback on the pituitary gland; high cortisol with concomitantly low ACTH isolates the pathology exclusively to the adrenal gland.
2
Differentiate ACTH-dependent hypercortisolism using the high-dose dexamethasone suppression test.
Suppression of cortisol identifies a pituitary adenoma (Cushing disease). Lack of suppression identifies an ectopic ACTH source.
Pituitary adenomas generally retain high-threshold negative feedback receptors, whereas ectopic tumors are completely autonomous.
3
Evaluate hypocortisolism profiles based on ACTH and electrolyte levels.
High ACTH with hyperkalemia indicates primary adrenal destruction. Low ACTH with normal potassium indicates pituitary failure.
Aldosterone secretion is primarily governed by the renin-angiotensin system and potassium levels, not ACTH. Therefore, secondary adrenal insufficiency spares mineralocorticoid function.

Key Concept

Differentiation of hypothalamic-pituitary-adrenal axis pathologies using ACTH levels, high-dose dexamethasone suppression testing, and mineralocorticoid markers.
Question 1733Question →

A 19-year-old male is brought to the urgent care clinic by his parents due to extreme fatigue, increased thirst, and frequent urination over the past week. Today, he developed nausea and deep, rapid breathing. Laboratory evaluation shows:

Serum sodium: 138 mEq/L138 \text{ mEq/L}
Serum chloride: 104 mEq/L104 \text{ mEq/L}
Serum bicarbonate: 12 mEq/L12 \text{ mEq/L}

Arterial blood gas analysis on room air reveals:
pH: 7.247.24
PaCO2PaCO_2: 26 mm Hg26 \text{ mm Hg}
PaO2PaO_2: 95 mm Hg95 \text{ mm Hg}

Based on these findings, which of the following is the most accurate interpretation of this patient's acid-base status?

Show answer & explanation

Answer: Primary metabolic acidosis with adequate respiratory compensation

Answer

Primary metabolic acidosis with adequate respiratory compensation
The correct answer accurately identifies the patient's condition. The pH of 7.24 indicates acidemia, and the low bicarbonate level of 12 mEq/L establishes metabolic acidosis as the primary disorder. To determine if the respiratory compensation is appropriate, Winter's formula is used: Expected PaCO2=(1.5×HCO3−)+8±2PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2. For this patient, the calculation yields (1.5×12)+8=26±2 mm Hg(1.5 \times 12) + 8 = 26 \pm 2 \text{ mm Hg}. Since the patient's actual PaCO2PaCO_2 is exactly 26 mm Hg, the respiratory compensation is adequate, and there is no secondary acid-base disturbance.

Step-by-Step Solution

1
Identify the primary acid-base disturbance by evaluating the pH and serum bicarbonate.
The pH is 7.24 (acidemia) and bicarbonate is 12 mEq/L (low).
A low pH combined with a proportionally low bicarbonate level confirms that the primary process is a metabolic acidosis.
2
Calculate the expected respiratory compensation using Winter's formula.
Expected PaCO2=(1.5×12)+8±2=26±2 mm HgPaCO_2 = (1.5 \times 12) + 8 \pm 2 = 26 \pm 2 \text{ mm Hg}.
In primary metabolic acidosis, the lungs rapidly compensate by blowing off CO2CO_2 (hyperventilation) to raise the pH. Winter's formula predicts the expected PaCO2PaCO_2 range for a given bicarbonate level.
3
Compare the actual PaCO2PaCO_2 to the expected PaCO2PaCO_2.
The patient's actual PaCO2PaCO_2 is 26 mm Hg, which falls exactly within the expected range.
Because the actual PaCO2PaCO_2 matches the calculated value, the respiratory compensation is fully adequate, meaning there is no superimposed secondary respiratory disorder.

Key Concept

Applying Winter's formula to evaluate respiratory compensation in primary metabolic acidosis
Question 1734Question →

Match each patient's clinical presentation with the most characteristic peripheral blood smear finding.

Click a left item, then click its matching right item

Items

A 65-year-old man with massive splenomegaly, fatigue, and a bone marrow biopsy showing extensive collagen deposition.
A 24-year-old woman with systemic lupus erythematosus who rapidly develops jaundice and severe anemia.
A 45-year-old man with severe sepsis who develops diffuse oozing from venipuncture sites and acute kidney injury.
A 19-year-old man who develops dark urine and scleral icterus three days after taking trimethoprim-sulfamethoxazole.
A 50-year-old woman with chronic alcohol use disorder, distal extremity numbness, and an elevated mean corpuscular volume.

Matches

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Answer

Myelofibrosis pairs with teardrop cells. Warm AIHA pairs with spherocytes. DIC pairs with schistocytes. G6PD deficiency pairs with bite cells. Vitamin B12 deficiency pairs with macro-ovalocytes and hypersegmented neutrophils.
Each clinical presentation contains classic pathognomonic features that correspond to a specific mechanism of red blood cell destruction or altered production. Understanding the underlying pathophysiology—marrow fibrosis (teardrop cells), immune-mediated membrane loss (spherocytes), mechanical shearing (schistocytes), oxidative damage (bite cells), and impaired DNA synthesis (macro-ovalocytes/hypersegmented neutrophils)—allows for direct matching of the disease process to its microscopic manifestation.

Step-by-Step Solution

1
Analyze the first vignette: A 65-year-old with massive splenomegaly and marrow collagen deposition.
Identify primary myelofibrosis, which leads to extramedullary hematopoiesis and structurally deformed erythrocytes.
Bone marrow fibrosis physically distorts red blood cells as they exit the marrow space, producing dacrocytes (teardrop cells).
2
Analyze the second vignette: A 24-year-old with SLE presenting with acute jaundice and anemia.
Identify warm autoimmune hemolytic anemia (AIHA).
SLE frequently causes warm AIHA. Splenic macrophages remove sections of antibody-coated RBC membranes, causing the cells to round up into spherocytes.
3
Analyze the third vignette: A 45-year-old with sepsis, oozing from venipuncture sites, and renal failure.
Identify disseminated intravascular coagulation (DIC), a microangiopathic hemolytic anemia.
Systemic activation of the coagulation cascade forms microthrombi (fibrin webs) that shear passing red blood cells into schistocytes.
4
Analyze the fourth vignette: A 19-year-old with acute hemolysis after taking a sulfa drug.
Identify Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency.
Oxidative stress leads to hemoglobin denaturation (Heinz bodies). The spleen plucks out these inclusions, leaving bite cells (degmacytes).
5
Analyze the fifth vignette: A 50-year-old with alcohol use disorder, neuropathy, and macrocytosis.
Identify megaloblastic anemia, likely due to Vitamin B12 deficiency.
Defective DNA synthesis leads to nuclear-cytoplasmic asynchrony, producing large, oval red blood cells and hypersegmented neutrophils.

Key Concept

Correlation of peripheral blood smear findings with specific hematologic and oncologic disorders.
Question 1735Question →

A 42-year-old male patient is admitted to the intensive care unit for the management of severe acute pancreatitis. On presentation, he was tachycardic and hypotensive. Over the initial 24 hours of admission, he received 7 liters of 0.9% sodium chloride intravenously for aggressive fluid resuscitation. His vital signs are now stable. Laboratory studies obtained on hospital day 2 reveal the following:

Serum sodium: 142 mEq/L142 \text{ mEq/L}
Serum potassium: 4.2 mEq/L4.2 \text{ mEq/L}
Serum chloride: 115 mEq/L115 \text{ mEq/L}
Serum bicarbonate: 15 mEq/L15 \text{ mEq/L}
Blood urea nitrogen: 18 mg/dL18 \text{ mg/dL}
Serum creatinine: 0.9 mg/dL0.9 \text{ mg/dL}

Arterial blood gas on room air shows:
pH: 7.287.28
PaCO2PaCO_2: 30 mmHg30 \text{ mmHg}
PaO2PaO_2: 92 mmHg92 \text{ mmHg}

Which of the following is the most likely mechanism underlying this patient's current acid-base abnormality?

Show answer & explanation

Answer: Intravenous administration of a fluid with a supraphysiologic chloride concentration

Answer

Intravenous administration of a fluid with a supraphysiologic chloride concentration
This patient has a normal anion gap metabolic acidosis. The anion gap is calculated as Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-), which in this case is 142−(115+15)=12 mEq/L142 - (115 + 15) = 12 \text{ mEq/L} (normal is typically 8-12 mEq/L). The compensatory respiratory response is appropriate, as confirmed by Winter's formula: expected PaCO2=(1.5×15)+8=30.5±2 mmHgPaCO_2 = (1.5 \times 15) + 8 = 30.5 \pm 2 \text{ mmHg}, matching the measured value of 30 mmHg. The cause of this isolated, normal anion gap metabolic acidosis is the aggressive fluid resuscitation with 0.9% normal saline. Normal saline is actually supraphysiologic in its chloride content (154 mEq/L compared to a normal serum chloride of ~100 mEq/L). Massive infusion expands the extracellular volume and drives up serum chloride, which causes a relative decrease in serum bicarbonate to maintain electrical neutrality, resulting in hyperchloremic metabolic acidosis.

Step-by-Step Solution

1
Identify the primary acid-base disorder.
The pH is acidemic (7.28) and the serum bicarbonate is low (15 mEq/L), indicating a primary metabolic acidosis.
Establishing the primary disorder dictates which compensatory formulas and diagnostic algorithms to use.
2
Calculate the serum anion gap.
Anion Gap = Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-) = 142−(115+15)142 - (115 + 15) = 12 mEq/L12 \text{ mEq/L}.
Metabolic acidosis must be classified into high anion gap or normal anion gap (hyperchloremic) to narrow the differential diagnosis.
3
Calculate the expected respiratory compensation.
Using Winter's formula: Expected PaCO2=(1.5×15)+8=30.5±2PaCO_2 = (1.5 \times 15) + 8 = 30.5 \pm 2. The actual PaCO2PaCO_2 is 30 mmHg, which is perfectly compensated.
Checking compensation ensures there is no superimposed primary respiratory acid-base disorder.
4
Determine the cause of the normal anion gap metabolic acidosis.
The patient received 7 liters of 0.9% sodium chloride, which contains 154 mEq/L of chloride (supraphysiologic compared to the normal serum level of ~100 mEq/L), leading to hyperchloremic acidosis.
Correlating the calculated laboratory derangement with the clinical history provides the final diagnosis.

Key Concept

Normal saline (0.9% NaCl) contains 154 mEq/L of chloride. Large volume resuscitation with this fluid causes a hyperchloremic, normal anion gap metabolic acidosis.
Estimated Time:1m 0s
Question 1736Question →

Match each clinical presentation of infective endocarditis with the most appropriate empiric or targeted antimicrobial regimen.

Click a left item, then click its matching right item

Items

A 55-year-old man with native valve endocarditis caused by methicillin-susceptible Staphylococcus aureus (MSSA) and no known drug allergies.
A 68-year-old woman with suspected prosthetic valve endocarditis, presenting with fever and a new murmur 3 months after a surgical aortic valve replacement.
A 72-year-old man with native valve endocarditis caused by Enterococcus faecalis and a history of severe chronic kidney disease.
A 45-year-old woman with subacute native valve endocarditis caused by Streptococcus gallolyticus that is highly susceptible to penicillin.

Matches

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Answer

The correct matches are: Native valve MSSA endocarditis pairs with IV cefazolin or nafcillin; early prosthetic valve endocarditis pairs with IV vancomycin, gentamicin, and rifampin; Enterococcal endocarditis in a patient with chronic kidney disease pairs with IV ampicillin plus ceftriaxone; and highly penicillin-susceptible Streptococcus gallolyticus endocarditis pairs with IV penicillin G or ceftriaxone monotherapy.
Each pathogen and clinical scenario in infective endocarditis requires a specific, guideline-directed antimicrobial regimen to ensure bactericidal activity, penetrate biofilms on prostheses, and minimize systemic toxicity.

Step-by-Step Solution

1
Analyze the antimicrobial requirement for MSSA native valve endocarditis.
Identify that beta-lactam therapy (nafcillin, oxacillin, or cefazolin) is superior to vancomycin.
Beta-lactams provide faster bacteremia clearance and better clinical outcomes for MSSA infections.
2
Evaluate the patient with suspected early prosthetic valve endocarditis (PVE).
Select a broad-spectrum, three-drug regimen: vancomycin, gentamicin, and rifampin.
Early PVE is frequently caused by coagulase-negative staphylococci; vancomycin provides MRSA/MRSE coverage, rifampin penetrates biofilms, and gentamicin provides early synergy.
3
Assess the treatment for Enterococcus faecalis endocarditis in a patient with severe chronic kidney disease.
Select ampicillin combined with ceftriaxone.
Enterococci require synergistic therapy for bactericidal activity. Ampicillin plus ceftriaxone avoids the nephrotoxicity associated with the alternative ampicillin plus gentamicin regimen.
4
Review the optimal therapy for highly penicillin-susceptible Streptococcus gallolyticus endocarditis.
Select monotherapy with penicillin G or ceftriaxone.
Monotherapy is highly effective for exquisitely susceptible streptococci and avoids unnecessary exposure to broader-spectrum agents or aminoglycosides.

Key Concept

Appropriate antimicrobial selection for infective endocarditis depends heavily on the causative pathogen, the presence of prosthetic material (requiring biofilm penetration), and patient-specific comorbidities such as underlying renal dysfunction.
Question 1737Question →

A 45-year-old man presents to the clinic reporting episodic headaches, severe diaphoresis, and palpitations. His blood pressure during these episodes is typically around 180/110 mm Hg. The physician strongly suspects a pheochromocytoma. Arrange the following clinical steps in the correct chronological sequence for the standard diagnosis and definitive management of this condition.

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Answer

The correct sequential order is: Biochemical testing, followed by Abdominal imaging, followed by Alpha-blockade, followed by Beta-blockade, and finally Surgical resection.
The standard sequence for pheochromocytoma diagnosis and management relies heavily on establishing biochemical proof of catecholamine excess first (via metanephrines). Only after this biochemical confirmation is anatomical imaging (CT or MRI) utilized to locate the tumor, ensuring that any discovered masses are clinically relevant and functional. Once the tumor is localized, the patient must be prepared for surgery using sequential medical blockade to prevent an intraoperative hypertensive crisis. This medical optimization strictly starts with alpha-adrenergic blockers (e.g., phenoxybenzamine) to induce vasodilation and restore intravascular volume, followed subsequently by beta-adrenergic blockers to control reactive tachycardia. Finally, once the patient is hemodynamically stable, the definitive treatment is surgical resection (adrenalectomy).

Step-by-Step Solution

1
Identify the suspected diagnosis based on the clinical presentation.
The patient's classic triad of episodic headaches, diaphoresis, and tachycardia, along with episodic severe hypertension, points directly to a pheochromocytoma.
Establishing the primary differential diagnosis dictates the specific diagnostic and management algorithm.
2
Determine the initial diagnostic step.
Measure plasma free metanephrines or 24-hour urine fractionated metanephrines.
Biochemical proof of a functional tumor must precede imaging to avoid discovering and erroneously acting upon non-functional adrenal incidentalomas.
3
Determine the localization step.
Perform CT or MRI of the abdomen.
Imaging is required to locate the biochemically confirmed pheochromocytoma prior to surgical planning.
4
Determine the preoperative medical management sequence.
Start alpha-blockade first, followed days later by beta-blockade.
Alpha-blockade (e.g., phenoxybenzamine) prevents severe intraoperative hypertension and allows for volume expansion. Beta-blockade is added later strictly for heart rate control; if given before alpha-blockade, it causes unopposed alpha-1 vasoconstriction and a potentially fatal hypertensive crisis.
5
Determine the definitive therapeutic intervention.
Laparoscopic adrenalectomy.
Once the patient is fully medically optimized and hemodynamically stable, surgical removal of the tumor provides the definitive cure.

Key Concept

The standard approach to a suspected pheochromocytoma follows a strict sequence: biochemical confirmation first, followed by anatomical localization, then preoperative sequential alpha-adrenergic and beta-adrenergic blockade, and finally surgical resection.
Question 1738Question →

A 22-year-old woman is brought to the emergency department 4 hours after intentionally ingesting an unknown quantity of pills. She complains of ringing in her ears, nausea, and diffuse abdominal pain. Her temperature is 37.8°C (100.0°F), blood pressure is 110/70 mm Hg, pulse is 115/min, and respirations are 26/min.

Laboratory studies show:
TestValue
Serum sodium140 mEq/L
Serum potassium3.5 mEq/L
Serum chloride104 mEq/L
Serum bicarbonate14 mEq/L
Blood urea nitrogen18 mg/dL
Serum creatinine0.9 mg/dL
Arterial blood gas analysis on room air:
TestValue
pH7.42
PaCO222 mm Hg
PaO298 mm Hg

Which of the following best characterizes this patient's primary acid-base disturbance(s)?

Show answer & explanation

Answer: Mixed high anion gap metabolic acidosis and primary respiratory alkalosis

Answer

Mixed high anion gap metabolic acidosis and primary respiratory alkalosis
This patient has a mixed acid-base disorder characteristic of acute salicylate toxicity (indicated by tinnitus, nausea, and hyperventilation). Step 1: The anion gap is 140−(104+14)=22140 - (104 + 14) = 22, confirming a high anion gap metabolic acidosis. Step 2: To check for appropriate respiratory compensation, Winter's formula is applied: ExpectedPaCO2=(1.5×14)+8±2=29±2Expected PaCO_2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2. Step 3: The patient's measured PaCO2 is 22 mm Hg, which is lower than the expected 27-31 mm Hg range. This indicates an excessive respiratory drive beyond what is needed for compensation, signifying an independent primary respiratory alkalosis. Step 4: The delta-delta ratio is (22−12)/(24−14)=1.0(22 - 12) / (24 - 14) = 1.0, which rules out any additional primary metabolic alkalosis or non-anion gap metabolic acidosis.

Step-by-Step Solution

1
Calculate the anion gap to determine if a primary metabolic acidosis is present.
AnionGap=Na+−(Cl−+HCO3−)=140−(104+14)=22 mEq/LAnion Gap = Na^+ - (Cl^- + HCO_3^-) = 140 - (104 + 14) = 22 \text{ mEq/L}.
An elevated anion gap (>12 mEq/L) establishes the presence of a primary high anion gap metabolic acidosis (AGMA).
2
Apply Winter's formula to determine the expected respiratory compensation for the metabolic acidosis.
ExpectedPaCO2=(1.5×HCO3−)+8±2=(1.5×14)+8±2=29±2 mm HgExpected PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2 \text{ mm Hg}. The expected range is 27 to 31 mm Hg.
Winter's formula determines if the patient's respiratory drive is appropriately compensating for the metabolic acidosis or if there is a secondary respiratory disorder.
3
Compare the measured PaCO2 to the expected PaCO2.
The measured PaCO2PaCO_2 is 22 mm Hg, which is lower than the expected range of 27-31 mm Hg.
Because the measured PaCO2 is lower than the expected appropriate compensation, an independent primary respiratory alkalosis is present.
4
Calculate the delta-delta ratio to evaluate for an additional covert metabolic disorder.
ΔAG/ΔHCO3−=(22−12)/(24−14)=10/10=1.0\Delta AG / \Delta HCO_3^- = (22 - 12) / (24 - 14) = 10 / 10 = 1.0.
A ratio between 1 and 2 indicates a pure high anion gap metabolic acidosis without a concurrent primary metabolic alkalosis or non-anion gap metabolic acidosis.

Key Concept

Patients with salicylate toxicity typically present with a mixed high anion gap metabolic acidosis (due to uncoupling of oxidative phosphorylation) and a primary respiratory alkalosis (due to direct stimulation of the medullary respiratory center).
Question 1739Question →

A 6262-year-old man is evaluated on postoperative day 66 following a right total knee arthroplasty. He complains of new-onset swelling and pain in his right calf. The patient has been receiving subcutaneous unfractionated heparin for deep venous thrombosis prophylaxis since his surgery. He has no other medical history and takes no other medications. Vital signs are normal. Physical examination shows a swollen, erythematous, and tender right calf.

Laboratory results:

TestResult
Hemoglobin13.2 g/dL13.2 \text{ g/dL}
Platelet count (Day 0)260,000/μL260,000/\mu\text{L}
Platelet count (Day 6)110,000/μL110,000/\mu\text{L}

A duplex ultrasound of the right lower extremity reveals a new noncompressible segment in the right popliteal vein. Which of the following is the most appropriate next step in the management of this patient?

Show answer & explanation

Answer: Discontinue unfractionated heparin and initiate argatroban

Answer

Discontinue unfractionated heparin and initiate argatroban
This patient's presentation is highly characteristic of Heparin-Induced Thrombocytopenia (HIT) type 2. HIT is an immune-mediated, prothrombotic disorder caused by the development of IgG antibodies against heparin-platelet factor 4 (PF4) complexes. It is classically suspected when a patient experiences a platelet count drop of greater than 50%50\% from baseline, typically occurring 55 to 1010 days after the initiation of unfractionated or low-molecular-weight heparin. This patient's count dropped from 260,000/μL260,000/\mu\text{L} to 110,000/μL110,000/\mu\text{L} on day 66. Furthermore, the condition paradoxically causes severe thrombosis rather than bleeding, evidenced here by the new popliteal deep venous thrombosis. When HIT is clinically suspected (e.g., high 4T score), immediate empiric treatment is required before waiting for confirmatory laboratory testing. All heparin products must be immediately discontinued. Because the patient has a new thrombosis and remains at high risk for further clots, therapeutic anticoagulation must be rapidly established using a non-heparin agent. Direct thrombin inhibitors (such as argatroban or bivalirudin) or the indirect factor Xa inhibitor fondaparinux are the preferred therapies.

Step-by-Step Solution

1
Calculate the magnitude of the platelet drop and note the timing.
The platelet count dropped by more than 50%50\% (from 260,000260,000 to 110,000110,000) over 66 days of heparin therapy.
A >50%>50\% drop in platelets occurring 55 to 1010 days after heparin initiation strongly suggests Heparin-Induced Thrombocytopenia (HIT).
2
Assess for clinical complications associated with the thrombocytopenia.
The patient has a new deep venous thrombosis (DVT) in the popliteal vein.
HIT is a highly prothrombotic state. The combination of typical timing, severe platelet drop, and new thrombosis yields a high '4T' score, making HIT the presumptive diagnosis.
3
Determine the necessary immediate medical intervention.
All heparin products must be stopped immediately, and therapeutic anticoagulation with a non-heparin agent (e.g., argatroban) must be started.
Stopping heparin halts the immune reaction, and a direct thrombin inhibitor provides the necessary anticoagulation to treat the new DVT without cross-reacting with HIT antibodies.

Key Concept

Patients who develop a >50%>50\% drop in platelets and new thrombosis 5−105-10 days after starting heparin have Heparin-Induced Thrombocytopenia (HIT). Management requires immediate cessation of all heparin products and initiation of a non-heparin anticoagulant like argatroban.
Question 1740Question →

A 45-year-old woman with a history of diffuse cutaneous systemic sclerosis is evaluated in the clinic for worsening episodes of painful digital color changes (white to blue to red) triggered by cold exposure. She currently takes no medications for this issue. Arrange the following interventions in the most appropriate stepwise escalation sequence for managing her Raynaud phenomenon, starting with the initial management step and progressing to therapies for refractory, severe disease with impending digital ischemia.

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Answer

The correct sequence for managing Raynaud phenomenon escalates from conservative measures to calcium channel blockers, then to phosphodiesterase-5 inhibitors, and finally to intravenous prostanoids for severe disease.
The management of Raynaud phenomenon is step-wise. It begins universally with lifestyle modifications (cold avoidance, smoking cessation). If symptoms persist, first-line pharmacologic therapy is an oral dihydropyridine calcium channel blocker (e.g., amlodipine). If still refractory, a phosphodiesterase-5 inhibitor (e.g., sildenafil) is typically added. For severe, refractory cases presenting with critical digital ischemia or active digital ulcers, intravenous prostanoids (e.g., epoprostenol) or endothelin receptor antagonists (e.g., bosentan) are indicated.

Step-by-Step Solution

1
Identify the underlying condition and its initial non-pharmacologic management.
The patient has Raynaud phenomenon secondary to systemic sclerosis. Initial management begins with conservative measures.
Non-pharmacologic interventions form the baseline for managing Raynaud phenomenon and minimizing vasospastic triggers.
2
Determine the first-line pharmacologic therapy for symptomatic disease.
Oral dihydropyridine calcium channel blockers are indicated.
When conservative measures are insufficient, these agents act as direct vasodilators to reduce the frequency and severity of ischemic attacks.
3
Identify the appropriate escalation for symptoms refractory to first-line agents.
Addition of a phosphodiesterase-5 inhibitor.
These medications provide additive vasodilatory effects by increasing cGMP availability in vascular smooth muscle.
4
Determine the treatment for severe, refractory disease or critical digital ischemia.
Intravenous prostanoids or endothelin receptor antagonists.
These are potent vasodilators and remodeling agents reserved for severe complications like digital ulcers.

Key Concept

Management of secondary Raynaud phenomenon follows a step-wise escalation from conservative lifestyle measures to oral vasodilators (starting with calcium channel blockers), followed by advanced therapies (like IV prostanoids) for refractory ischemic complications.
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