A 45-year-old woman reports a recent history of kidney stones, depression, weakness and increased urination. She now has lower left jaw pain, and the radiograph shows an expansile lesion of the left mandible. Which laboratory value is MOST likely elevated?

Correct answer: B. Parathyroid hormone

• A. Vitamin D excess can raise calcium, but it does not cause brown tumors, and the clinical picture described is classic for PTH excess.
• B. Correct. This is HYPERPARATHYROIDISM. Excess PTH (usually from a parathyroid adenoma) drives osteoclastic bone resorption, producing the 'BROWN TUMOR' — a lesion radiographically and histologically identical to a central giant cell granuloma. Serum PTH and CALCIUM are elevated; phosphate is LOW. Other radiographic signs: loss of the lamina dura and a ground-glass trabecular pattern.
• C. Phosphate is DECREASED in primary hyperparathyroidism, because PTH promotes renal phosphate excretion.
• D. Thyroid hormone excess causes weight loss, tachycardia and heat intolerance — it does not produce brown tumors or this stone/bone/groan/moan picture.

Note: Classic mnemonic for hyperparathyroidism: 'painful bones, renal stones, abdominal groans, psychic moans.'