Hypophosphoremia secondary to idiopathic moderate phosphate diabetes: a differential diagnosis with primary fibromyalgia.

Sir, In 1990 the American College of Rheumatology defined the criteria for primary fibromyalgia (1). Before raising the possibility of this diagnosis, some disorders which may cause diffuse muscle, joint and tendon pain must be excluded. Hypophosphoremia due to moderate phosphate diabetes (MPD) could represent one of these differential diagnoses. We followed 11 patients in whom hypophosphoremia due to idiopathic MPD had been diagnosed (7 men and 4 women, mean age 48 yrs., range 40 65). The mean duration of the clinical symptoms before the diagnosis was 8 years (range 5 10 yrs.) and the mean follow-up period after the diagnosis was 3 years (range 1.5 9 yrs.). All patients presented with the ACR criteria for fibromyalgia: diffuse spinal pain at all levels with little relief obtained from rest, NSAIDS or analgesics; joint, muscle and tendon pain without objective abnormalities; and pain on palpation of at least 11 of 18 sensitive points. Six patients were depressed, 3 were declared unfit for work, and 4 had had calcium lithiasis. Serum and urine phosphate were determined by the phospho-molybdate reaction. The mean phosphoremia (Ph) before treatment was 0.69 ± 0.14 mmol/l and the mean TmpO4/GFR was 0.58 ± 0.14 mmol/l. Serum calcium and ionised calcium, creatin-