Endocrine Abstracts

Introduction: Pseudohypoparathyroidism is a rare group of heterogenous disorders. PHP1b consists of renal resistance to PTH in the absence of other physical or endocrine abnormalities and is associated with reduced 1,25-OH vitamin D synthesis, increased phosphate secretion and hypocalcaemia. Despite calcium and vitamin D replacement many patients still have chronically elevated PTH.

Case description: A 31-year-old white female presented with symptoms of tetany with her bloods revealing hypocalcaemia of 2.05 mmol/l, increased ALP (263 IU/l) and increased PTH (1100 ng/l). She had normal 25-hydroxycholecalciferol. The hand radiograph suggested osteitis fibrosa. Secondary hyperparathyroidism was excluded and diagnosis of pseudohypoparathyroidism was made and patient was commenced on vit D2 and calcium supplements. 25 years later she presented with hypercalcaemia, raised PTH and borderline low vit D levels and was switched from calcitriol to α-calcidiol which she stopped as she couldn’t tolerate the preparation. Her calcium levels remained elevated, vit D became undetectable and PTH soon exceeded 150 pmol/l. The DEXA scan showed L1–L4 osteopenia and US KUB-marked bilateral cortical thinning. US neck suggested left lower parathyroid adenoma confirmed by a Sestamibi scan which revealed a well defined 2×1 cm left inferior parathyroid adenoma and possibly a second intrathyroid 8 mm parathyroid adenoma. Patient was eventually established on 2200 units of cholecalciferol OD and weekly alendronate with normalisation of calcium and vitamin D levels and gradual decline in PTH levels. Decision was made not to proceed with parathyroidectomy as it could potentially lead to hyperplasia of another parathyroid gland.

Conclusion: The management goal in PHP1b is to achieve normacalcaemia and maintain PTH as low as possible. However, PHP1b patients are at risk of developing tertiary hyperparathyroidism.