The finding of the elevated serum calcium concentration is usually the first clue of hyperparathyroidism and when hypercalcemia is confirmed by repeat sampling, all of causes should be considered.
　　A29-year-old man presented to the emergency department with urinary incontinence that began suddenly five days earlier. He had weakness in both legs (muscle power decreased to 4/5) with numbness. Upon investigation, the patient had hypercalcemia (serum calcium 3.485 [normal range 1.975–2.475] mmol/L) and hypophosphatemia (serum phosphate 0.581 [normal range 0.775– 1.518] mmol/L) with an elevated level of intact parathyroid hormone (1956 [normal range 14–72] ng/mL). Magnetic resonance imaging of his spine showed two lesions over posterior elements of T10 and L4, with compression of the spinal cord at T10. The patient had an urgent surgical decompression of the T10 lesion, which, on histology, was composed of round to spindled mononuclear cells and numerous osteoclast-type giant cells with some bony trabeculae.
What disease should be considered first?