Phosphate deficiency as a rare cause of osteomalacia--case report of several years of enteral feeding and antacid therapy

HISTORY AND CLINICAL FINDINGS: Floor-of-the-mouth cancer had been diagnosed and surgically treated in a 55-year-old man 4 years before the latest admission. For the last 3 years he had been fed through a percutaneous endoscopic gastrostomy (PEG). Since then he had experienced reflux oesophagitis which was being treated with aluminium-containing antacids. He was hospitalized for the surgical treatment of bilateral fractures of the neck of the femur. A surgical biopsy revealed osteomalacia but no metastasis. INVESTIGATIONS: The serum phosphate level was significantly reduced (0.21 mmol/l) and there was no detectable phosphate excretion in the 24-hour urine. Serum calcium concentration was unremarkable, but there was hypercalciuria (34.4 mmol/d). Alkaline phosphate activity was significantly raised (393 U/l) and parathormone level reduced (7 ng/l). Vitamin D concentration was unremarkable. TREATMENT AND COURSE: The phosphate content in the parenteral feed was at first increased and additional phosphate was given by mouth. The calcium and phosphate levels slowly became normal only after medication had been changed from antacids to H2-blockers. CONCLUSIONS: In this case osteomalacia was caused not by vitamin D deficiency but by a lack of phosphate. The reduced intestinal phosphate absorption by the antacids only partially explains the pronounced clinical signs. If antacids are taken over long periods the phosphate balance should be carefully monitored to avoid osteomalacia.