A 52-year-old woman from rural Maharashtra presents with progressive bone pain, muscle weakness, and recurrent kidney stones over 18 months. Laboratory investigations reveal: serum calcium 11.2 mg/dL (normal 8.5–10.5), phosphate 2.1 mg/dL (normal 2.5–4.5), alkaline phosphatase 95 U/L (normal 30–120), and PTH 245 pg/mL (normal 10–65). Serum creatinine is 1.1 mg/dL. A chest X-ray is normal. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Primary Hyperparathyroidism ### Key Findings | Parameter | Patient Value | Normal Range | Interpretation | |-----------|---------------|--------------|----------------| | Serum Calcium | 11.2 mg/dL | 8.5–10.5 | **Elevated** | | Phosphate | 2.1 mg/dL | 2.5–4.5 | **Low** | | PTH | 245 pg/mL | 10–65 | **Markedly elevated** | | Creatinine | 1.1 mg/dL | 0.6–1.2 | Normal (rules out CKD) | | ALP | 95 U/L | 30–120 | Normal | ### Pathophysiology **Key Point:** Primary hyperparathyroidism is autonomous PTH secretion from a parathyroid adenoma, hyperplasia, or carcinoma, causing hypercalcemia and hypophosphatemia independent of serum calcium feedback. 1. Autonomous PTH production → increased renal calcium reabsorption and phosphate wasting 2. PTH stimulates 1,25-dihydroxyvitamin D production → increased intestinal calcium absorption 3. Result: **high calcium + low phosphate + high PTH** ### Clinical Presentation Correlation - **Bone pain & weakness:** Osteitis fibrosa cystica (high bone turnover from chronic PTH excess) - **Kidney stones:** Hypercalciuria and hyperphosphaturia from PTH-mediated renal effects - **Normal renal function:** Excludes secondary/tertiary hyperparathyroidism (which require CKD) ### Why This Is Primary, Not Secondary/Tertiary **High-Yield:** - **Primary:** Normal/high calcium + high PTH + normal renal function = autonomous gland disease - **Secondary:** Low calcium + high PTH + CKD (creatinine >1.5, usually) - **Tertiary:** High calcium + high PTH + history of CKD (this patient has normal creatinine and no CKD history) This patient has normal renal function, making secondary and tertiary hyperparathyroidism unlikely. ### Differential Exclusion **Vitamin D intoxication:** Would show high calcium but **low PTH** (suppressed by hypercalcemia), not elevated PTH. Chest X-ray would often show granulomas (sarcoidosis). [cite:Harrison 21e Ch 296] **Clinical Pearl:** The combination of **hypercalcemia + hypophosphatemia + elevated PTH** in a patient with normal renal function is pathognomonic for primary hyperparathyroidism.