A 50-year-old man presented with multiple pathological fractures. His serum calcium was 11.5 mg/dl and phosphate was 2.5 mg/dl. Alkaline phosphatase was 940 I.U./dl. The most probable diagnosis is –
**Core Concept**
The patient's presentation suggests a disorder of calcium and phosphate metabolism, with hypercalcemia, hypophosphatemia, and elevated alkaline phosphatase levels. This profile is characteristic of a bone disease involving increased bone turnover and resorption.
**Why the Correct Answer is Right**
The patient's hypercalcemia and hypophosphatemia, combined with the elevated alkaline phosphatase, point towards a diagnosis of **hyperparathyroidism**. This condition is caused by an overproduction of parathyroid hormone (PTH), which stimulates the osteoclasts to break down bone, releasing calcium into the bloodstream and leading to hypophosphatemia. The elevated alkaline phosphatase is due to increased bone turnover and the activity of osteoblasts.
**Why Each Wrong Option is Incorrect**
**Option A:** Osteomalacia is characterized by a decrease in bone mineralization, which would result in hypocalcemia, not hypercalcemia, and would not typically present with such high levels of alkaline phosphatase.
**Option B:** Hypophosphatasia is a rare genetic disorder that results in low alkaline phosphatase levels, which is the opposite of what is seen in this patient.
**Option C:** Paget's disease is a localized bone disease that can cause hypercalcemia, but it typically presents with localized bone pain and deformity, and the alkaline phosphatase levels are usually much higher than normal.
**Clinical Pearl / High-Yield Fact**
Remember that hyperparathyroidism can present with a wide range of symptoms, including kidney stones, peptic ulcers, and neuropsychiatric symptoms, and that the diagnosis should be suspected in any patient with unexplained hypercalcemia.
**Correct Answer: C. Paget's disease is a localized bone disease that can cause hypercalcemia, but it typically presents with localized bone pain and deformity, and the alkaline phosphatase levels are usually much higher than normal.**