A unique case of adult hypophosphatemic osteomalacia

A 36-year-old Russian man presented with neck and low back pain in September 1990. He was of normal stature, and there were no stigmata of rickets. The family history was negative for bone disease. He was found to have hypophosphatemia (2.3 mg/dl), impaired phosphate reabsorption (TmP/GFR 2.08), hyperphosphatasemia (254 IU/l), normocalcemia, normal vitamin D metabolite levels, and secondary hyperparathyroidism. Clinically, his spinal movements were quite impaired and there was moderate proximal muscle weakness. On skeletal radiographs, there was generalized osteosclerosis and multiple ligamentous calcifications. Transiliac biopsy was diagnostic for severe osteomalacia. He was treated with oral phosphate (240 mEq daily) and calcitriol (4 micrograms daily) with resultant very slow clinical, biochemical, and histomorphologic improvement. The patient had hypophosphatemic osteomalacia with some features of X-linked hypophosphatemia, but sporadic and of relatively late onset. The osteopenia, height loss, incapacitating weakness, and glycinuria that are characteristics of sporadic adult onset nonfamilial hypophosphatemia, with or without an associated tumor, and the low serum calcitriol levels that may be an additional characteristic of tumor-induced osteomalacia were absent. Other known causes of acquired renal tubular dysfunction were ruled out. The etiology, pathogenesis, and nosology of the disorder remain obscure, but treatment based on experience with other forms of hypophosphatemic osteomalacia was ultimately effective.