[Idiopathic hypophosphataemic osteomalacia (author's transl)]

In an adult with sporadic idiopathic osteomalacia an increased phosphate clearance, hypophosphataemia, normocalcaemia, normal serum-25-hydroxycalciferol and an only slightly increased immunoreactive parathormone were found. Intestinal 47Ca absorption was clearly decreased. Radiologically and histologically there was a clear-cut defect of skeletal mineralisation. Under treatment with daily doses of 1-1.25 mg of vitamin D3 the 25-hydroxycalciferol level increased markedly, the immunoreactive parathormone decreased slightly. Serum calcium and hypophosphataemia remained unchanged and intestinal 47Ca absorption was improved. Already 4 weeks after commencing treatment pain and defective gait of the patient disappeared. Radiologically skeletal changes were improved after 7 months. However, histologically no significant bone healing had occurred. The biochemical findings of this disease correspond to those of familial hypophosphataemic (vitamin-D-resistant) rickets. The therapeutic effects of pharmacological doses of vitamin D resemble those in pseudo-vitamin-D-deficient rickets. The pathogenesis of idiopathic osteomalacia of the adult remains unclear. Vitamin D metabolism is unchanged as far as the stage of 25-hydroxycholecalciferol. It is unknown if a disorder of the renal synthesis of 1,25-dihydroxycholecalciferol or a peripheral resistance to the effects of this metabolite exists. In addition a defect of the tubular phosphate reabsorption independent of parathormone and vitamin D is assumed.