A 38-year-old male with a history of recurrent calcium oxalate nephrolithiasis undergoes metabolic workup. Laboratory results show hypercalcemia (serum calcium 2.85 mmol/L, normal 2.15-2.55), hypophosphatemia (0.65 mmol/L), and an inappropriately elevated serum Parathyroid Hormone (PTH) level of 115 pg/mL. What is the most common cause of this disorder?

Answer and explanation

Correct answer: A. Solitary benign parathyroid adenoma

  1. Step 1: Primary hyperparathyroidism is defined by autonomous oversecretion of PTH in the setting of hypercalcemia.
  2. Step 2: A solitary benign parathyroid adenoma accounts for approximately 80% to 85% of all cases of primary hyperparathyroidism.
Answer
Solitary benign parathyroid adenoma.
Why not the others: 'Parathyroid carcinoma' is extremely rare (< 1% of cases) and typically presents with severe life-threatening hypercalcemia (> 3.5 mmol/L) and palpable cervical mass; 'Familial hypocalciuric hypercalcemia' is an autosomal dominant defect in the calcium-sensing receptor with very low urinary calcium clearance; 'Tertiary hyperparathyroidism' occurs in end-stage renal disease with hyperphosphatemia.

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