[Hyperparathyroidism masked by osteomalacia. Is vitamin D administration in every case of osteomalacia problem-free?].

In a 71-year-old patient with osteomalacia, masked primary hyperparathyroidism was detected by vitamin D therapy for hypercalcemia. Surgery revealed a parathyroid tumor. Interpretation of total plasma calcium may be difficult unless the 25-hydroxyvitamin D levels are outside the normal range.