Adult hypophosphatemic osteomalacia: report of two cases

Two cases of late hypophosphatemic osteomalacia are described: a male aged 30 who had the disease since he was 22 and a woman of 23 who had the disease since she was 14. Both presented with myopathy and bone pain, and showed hypophosphatemia, hyperglycinuria, reduced tubular phosphate reabsorption (TPR), increased hydroxyprolinuria and normal iPTH and iCT values. Radiologically the male had no Looser's zones and the woman did. Bone biopsy confirmed hypophosphatemic osteomalacia. Both cases were treated with vitamin D and oral phosphate and no improvement was observed. When treatment with 25(OH)D3 was initiated, no improvement was seen and afterwards this was combined with treatment using 1.25(OH)2D3 and from this time on a clinical improvement of the myopathy became evident in both patients. In the woman, healing of the bone lesions occurred at the same time as that of the myopathy, whereas in the male the bone lesions became worse. Healing of the myopathy was only obtained when treatment with 1.25(OH)2D3 was begun. Both patients had reduced values of 2.3 erythrocytic DPG and low level of serum phosphorus when the myopathy was cured, which suggests a lack of effect of 2.3 DPG or serum phosphorus as a cause of the myopathy. Although this had been attributed to a deficiency in the function of 25(OH)D3, the response to 1.25(OH)2D3 and due to the effects of this metabolite on calcium transport in muscle, suggests that the myopathy which occurs in late hypophosphatemic osteomalacia is a result of deficiency or resistance to the muscular effect of this metabolite. We cannot explain the lack of bone healing in the man and further therapeutic studies are required.