Four cases of acquired hypophosphataemic (‘oncogenic’) osteomalacia. Problems of diagnosis, treatment and long‐term management

The insidious development of progressive bone pains and muscle weakness are well‐known features of osteomalacia which may have many causes [1]. Particular diagnostic difficulties are encountered in acquired hypophosphataemia, a condition associated with increased renal phosphate clearance [2] and low circulating 1,25dihydroxyvitamin D [1,25(OH)2D, calcitriol] [3, 4]. Many patients with this disease are shown to have benign tumours of mesenchymal origin with prominent fibrous and vascular characteristics [3, 4]. Cure is generally expected to follow surgical resection, with return of phosphate and 1,25(OH)2D levels to normal [3–5], indicating a likely causal relationship between tumour and both hypophosphataemia and 1,25(OH)2D production. Furthermore, experimental evidence supports a role for tumour products which influence both renal tubular cell phosphate transport and 1α‐hydroxylase activity [6–9]. The term ‘oncogenic hypophosphataemic osteomalacia’ (OHO) is now applied to this group. OHO was first recognized over 40 yr ago [10]. However, despite its musculoskeletal symptomology, it has only rarely been reported in the rheumatological literature [11–14]. Furthermore, most cases have been published as single case histories shortly after patients have appeared to be cured by surgery [3, 4]. Questions of diagnosis and management that have rarely been addressed include (i) the extent and methods of search for such tumours; (ii) the risk of relapse after surgery; (iii) the optimal drug treatment both in the initial stages and for long‐term control; and (iv) the risk of other long‐term complications. Additionally, the repeated reports of delays in diagnosis of up to 19 yr [4] suggest that the condition is poorly recognized. We therefore briefly present the case histories of four patients who have been followed for up to 23 yr, to illustrate each of these problems.