Adult onset idiopathic phosphate diabetes

This report describes the clinical and biologic data and bone density measurements in 19 adults seen in a rheumatology department, with phosphate diabetes defined by low serum phosphate levels and decreased tubular reabsorption of phosphate in the absence of known etiology. There were 14 males and 5 females with a mean age at disease onset of 36.7 years (20-68 years) and at diagnosis of 43.9 years (24-70 years). Axial pain was present in 17 patients (90%), radicular pain in 13 patients (68%), pain at night in 14 patients (74%), fatigue in 7 patients (37%), myalgia in 6 patients (32%), fracture in 6 patients (32%), renal colic in 4 patients (21%) and depression 10 patients (53%). Mean serum phosphorus was 2.25 mg/dL (1.08-2.76); maximum tubular reabsorption of phosphate/glomerular filtration rate was 0.58 (0.4-0.76) (n > 0.77). Calcium/creatinine > 0.48 was seen in 9 patients (47%), indicating an associated hypercalciuria. Serum calcium, sodium, magnesium, creatinine, cortisol, T3, T4, thyroid-stimulating hormone (TSH), 25 and 1,25 OH2 vitamin D3 were normal. Glucose and amino acid were absent from urine. Bone mineral density at L2-L4 level (Z-score) was -2.13 (-0.9 to -4.25), and at the femoral neck was -1.34(-1.5 to -3.2). Bone biopsy in 5 patients showed osteoporosis with minor osteoid deposition.Idiopathic phosphorus diabetes (IPD) is a rheumatic disease with chronic axial pain at night, radiculitis-like symptoms, fatigue and depression. In half of the patients, IPD is associated with hypercalciuria. Bone mineral density at L2-L4 and femoral neck level is low. Bone biopsies show osteoporosis. Chronic pain, fatigue and depression resulting from IPD may be improved by treatment with oral calcitriol and phosphorus. There might be a delay in improvement of a few months, even if the blood phosphate level is normalized. A 3% increase in bone mineral density could be measured at 6-month intervals when blood phosphate was maintained. This disease is often misdiagnosed when the maximal reabsorption rate of phosphorus is not calculated.