Hypophosphataemia

X-linked hypophosphataemia, also known as familial vitamin D-resistant rickets, is characterized by permanent hypophosphataemia resulting from renal tubular phosphate loss and decreased intestinal absorption of calcium. In this disorder, rickets is generally seen in the first 2 years of life, and remission usually follows closure of the growth plates; however, recurrence of symptoms is common later in life. Patients are typically short, bowlegged and stocky. Abnormalities in vitamin D metabolism have also been demonstrated in both X-linked hypophosphataemia and the Fanconi syndromes.

Radiographic features in children include rachitic changes at the growth plates and bowing of long bones, but deformity is frequently minimal. By adulthood, a generalized increase in bone density has occurred. Enthesopathic calcification and ossification develop in the paravertebral ligaments, anulus fibrosus and capsules of apophyseal and appendicular joints. Narrowing of the spinal canal as a result of ossification of the ligamentum flavum is common. Multiple sites of calcification are seen in the pelvis. Small ossicles may develop in the carpal bones and other osseous sites.

Hypophosphataemic vitamin D-refractory rickets and osteomalacia have been found to occur in association with various neoplasms of soft tissues or bone. The lesions typically are vascular and often show foci of new bone formation. Most commonly the tumour is a haemangiopericytoma. Bone lesions have included nonossifying fibroma, giant cell tumour, osteoblastoma, and non-neoplastic diseases such as fibrous dysplasia and neurofibromatosis.

Hypophosphataemic rickets has occurred after chemotherapy with ifosfamide.

DR