Endocrine Abstracts

We describe below a 72-year-old woman who presented clinically with short metacarpals and metatarsals and the following blood biochemistry: corrected calcium of 2.16 mmol/l (normal: 2.05–2.60), phosphate 0.61 mmol/l (normal: 0.8–1.45) and alkaline phosphatase of 108 U/l (normal: 35–104). She was 153 cm tall and weighed 109 kg with a round face. She had a history of Monoclonal Gammopathy of unknown significance, vitamin B12 deficiency and was admitted 10 years ago with a corrected calcium of 1.72 mmol/l and has been on alfacalcidol (1α-hydroxycholecalciferol) since then. Her current medications included alfacalcidol 1 μg on alternate days and vitamin B12 injection 1 mg every 3 months. On enquiry she informed that all her three siblings and one son have brachydactyly with none having low calcium. Further investigations showed a normal serum magnesium and a high parathyroid hormone of 7.6 pmol/l (normal: 1.1–6.9) with an ionised calcium of 1.07 mmol/l (normal: 1.05–1.30) and a phosphate of 0.64 mmol/l. Despite having the morphological features of Albright’s osteodystrophy a low phosphate was inconsistent with the diagnosis of pseudohypoparathyroidism type 1a. There was no provision for Ellsworth Howard test. A vitamin D level requested revealed severe vitamin D₃ deficiency (5.6 ng/ml; normal in summer: 10–60). She was thus diagnosed with pseudopseudohypoparathyroidism with vitamin D deficiency.

Pseudopseudohypoparathyroidism is considered to be an incomplete form of pseudohypoparathyroidism type 1a with normal blood biochemistry but abnormal morphological features of short height, excess weight, round face and brachydactyly. Her low calcium and phosphate and high parathyroid hormone levels were from vitamin D deficiency. There are reports of vitamin D deficiency mimicking pseudohypoparathyroidism type 2. Vitamin D deficiency also occurs in hyperparathyroidism but it is fairly uncommon in pseudopseudohypoparathyroidism. Thus vitamin D should always be measured in patients with abnormal calcium or phosphate level.