Pseudohypoparathyroidism Type 1b; a Rare Cause of Femoral Neck Fracture

A 6-year-old boy was seen in general pediatric clinic for assessment of possible rickets. He had hypocalcaemia and hyperphosphatemia. Serum calcium 1.47 mmol/L, phosphorus 2.5 mmol/L and alkaline phosphatase 1957 IU/L were recorded. Radiological X-ray of the hip showed multiple lytic lesions. The diagnosis of rickets was postulated with secondary hyperparathyroidism and was started on Vitamin D3 and oral calcium. He was treated for rickets at the age of one year. Parents were consanguineous. At the age of seven years, he presented to the emergency room with left femoral neck fracture following a minimal trauma which required open reduction and internal fixation. Physical examination revealed no dysmorphic features. Biochemical investigations revealed normal complete blood count, liver and renal functions and arterial blood gas. However, serum calcium was low 2.0 mmol/L, phosphorous 2.1 mmol/L and alkaline phosphatase 1752 IU/L, serum PTH was high 1406 ng/L with normal 25 (OH) Vit. D3 and 1,25 (OH)2 Vit. D3. Pseudohypoparathyroidism (PHP) is an uncommon metabolic bone disorder characterized by biochemical hypoparathyroidism (i.e.,hypocalcaemia and hyperphosphataemia), increased secretion of parathyroid hormone (PTH), and target tissue unresponsiveness to the biological actions of PTH. In addition, many patients with PHP exhibit a distinctive constellation of developmental and skeletal defects. Pseudohypoparathyroidism type 1b can be presented as skeletal fractures. We highlight the importance of this rare cause in differential diagnosis.