Type 1B pseudohypoparathyroidism is characterised by renal resistance to parathyroid hormone in the absence of other endocrine or physical abnormalities. We present a 36-year-old lady with pseudohypoparathyroidism diagnosed aged seven following seizures with hypocalcaemia, hyperphosphataemia, elevated alkaline phosphatase, elevated parathyroid hormone (PTH) at 700 pg/mL (<120) and no cyclic AMP response to bovine PTH. There was no family history or diagnostic phenotypic features. Treatment was commenced with 2 mcg alfacalcidol.
In 1999, serum alkaline phosphatase was elevated, with PTH 1946 ng/L (1272). Hand radiographs were normal. She was lost to follow-up. In 2002, radiological evidence of parathyroid bone disease was detected. Alendronate was commenced and bone densitometry requested.
Following non-traumatic fractures, she required bilateral hip replacements and humeral nailing. Serum calcium and phosphate were normal, although alkaline phosphatase was elevated, with PTH 2944 ng/L. No other causes of osteoporosis were identified. Treatment was changed to calcium carbonate 7.5 g and calcitriol 2 mcg in divided doses, with PTH falling to 1926 ng/L. Parathyroidectomy was performed. Repeated intravenous calcium and magnesium infusions were required post-operatively.
Recent bone biochemistry on calcitriol 2mcg was normal, with PTH 16.1 ng/L despite parathyroidectomy. Plain radiographs show healed fractures, with 75% improvement in cavitating lesions but residual cysts. The literature details resolution of overt osteitis fibrosa cystica in patients with pseudohypoparathyroidism treated with calcium and vitamin D. Our patient developed parathyroid bone disease despite vitamin D but responded to parathyroidectomy. Finger clubbing, previously reported with parathyroid bone disease due to renal failure, was also present.
This case illustrates the importance of preventing parathyroid bone disease and also suggests the need for early parathyroidectomy in those for whom medical therapy fails.