Endocrine Abstracts

Introduction: Pseudohypoparathyroidism (PHP) is a rare genetic disease characterized by renal resistance to parathyroid hormone (PTH), presenting with hypocalcemia, hyperphosphatemia and elevated PTH levels. We describe a PHP patient who presented with clinically significant hypercalcemia.

Case description: A 46-year-old woman with a prior history of hypocalcemia presented to the emergency department with new-onset hypercalcemia, renal failure and anemia. Blood gases showed a mild metabolic alkalosis. She had suffered recurrent hypocalcemic episodes throughout her life with elevated PTH levels and hypocalciuria, suggestive of PHP. Chronic medications included calcium 1800 mg/day, alfacalcidol (1α-OHD3) 3 mcg/day and cholecalciferol (vitamin D3) intermittently. A previous PTH infusion test supported the diagnosis of PHP. There were no Albright Hereditary Osteodystrophy (AHO) features, other hormone resistances or family history of calcium homeostasis dysregulation. Bearing these characteristics in mind, PHP type 1B seemed most likely and was subsequently proven by genetic testing. As for the cause of hypercalcemia, intoxication of calcium or Vitamin D was suspected and all supplements were stopped with rapid normalization of calcium levels. Laboratory 25-OHD3 and 1α,25-OHD3 levels were low. There was no evidence of malignancy. The patient subsequently became hypocalcemic and supplements were recommenced at lower doses. The patient remains normocalcemic since.

Discussion: Treatment modalities in PHP include calcium and hydroxylated vitamin D supplements. Aims of treatment include maintaining normocalcemia and normalizing PTH levels in order to avoid potentially deleterious skeletal effects of chronically elevated PTH levels. Hypercalcemia has been reported rarely in PHP, but more frequently in hypoparathyroidism due to milk alkali syndrome or vitamin D intoxication. We speculate that our patient’s hypercalcemia was caused by supplement overdose although vitamin D levels were not elevated and the patient denied increasing her regular calcium dose. The mild alkalosis and renal failure may allude to milk alkali syndrome. In conclusion, close surveillance is essential in PHP to prevent potentially life-threatening electrolyte disturbances.