Match each clinical and laboratory presentation with the most likely underlying pathophysi… — USMLE Step 2 CK

Match each clinical and laboratory presentation with the most likely underlying pathophysiologic mechanism.

A $32$ -year-old woman with recurrent calcium phosphate nephrolithiasis. Serum $K^+$ is $2.8$ mEq/L, $HCO_3^-$ is $14$ mEq/L, and urine pH is $6.8$ .Impaired alpha-intercalated cell hydrogen ion secretion
A $65$ -year-old man with diabetic nephropathy. Serum $K^+$ is $5.7$ mEq/L, $HCO_3^-$ is $18$ mEq/L, and urine pH is $5.2$ .Aldosterone deficiency or resistance at the collecting duct
A $24$ -year-old woman with fatigue and cramps. Blood pressure is $105/65$ mm Hg. Serum $K^+$ is $2.6$ mEq/L, $HCO_3^-$ is $32$ mEq/L, with significant hypocalciuria.Defect in the distal convoluted tubule sodium-chloride cotransporter
A $21$ -year-old man with early-onset severe hypertension ( $170/105$ mm Hg). Serum $K^+$ is $2.5$ mEq/L, $HCO_3^-$ is $31$ mEq/L, with undetectable plasma renin activity and serum aldosterone.Constitutive activation of the collecting duct epithelial sodium channel (ENaC)

Cevap

The correct matches are: the patient with nephrolithiasis and alkaline urine corresponds to impaired alpha-intercalated cell hydrogen ion secretion; the diabetic patient with hyperkalemia corresponds to aldosterone deficiency or resistance; the normotensive patient with hypocalciuria corresponds to a defect in the distal convoluted tubule sodium-chloride cotransporter; and the hypertensive patient with low renin/aldosterone corresponds to constitutive activation of the collecting duct epithelial sodium channel.

Each presentation aligns with a distinct tubular defect. Distal H+ secretion failure causes Type 1 RTA. Aldosterone deficiency causes Type 4 RTA. Na-Cl cotransporter defects cause Gitelman syndrome. ENaC overactivity causes Liddle syndrome.

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Analyze the acid-base and potassium status for each patient to categorize the broad pathophysiologic mechanism.

Two patients have metabolic acidosis with differing potassium levels (one low, one high), and two have metabolic alkalosis with hypokalemia.

Acid-base and potassium abnormalities act as the primary branching points for diagnosing renal tubular defects.

Differentiate the two patients with metabolic acidosis.

The hypokalemic patient with alkaline urine and kidney stones has distal (Type 1) RTA, caused by impaired H+ secretion. The hyperkalemic patient with acidic urine has Type 4 RTA, caused by aldosterone deficiency/resistance.

Urine pH and serum potassium are essential keys to distinguishing subtypes of normal anion gap metabolic acidosis.

Differentiate the two patients with metabolic alkalosis.

The normotensive patient with hypocalciuria has Gitelman syndrome (Na-Cl cotransporter defect). The severely hypertensive patient with suppressed renin and aldosterone has Liddle syndrome (ENaC overactivity).

Blood pressure and urine calcium levels distinguish between different causes of hypokalemic metabolic alkalosis.

Anahtar Kavram

Pathophysiology and clinical differentiation of renal tubular acidosis (RTA) and hereditary tubulopathies.

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