Masked primary (or tertiary) hyperparathyroidism.

Two patients are described in whom the preliminary clinical and laboratory investigations suggested a diagnosis of osteomalacia, from gluten-sensitive enteropathy in one and from anticonvulsant therapy in the other. However, when the primary disease was corrected by diet and extra vitamin D, respectively, both patients developed hypercalcaemia. A standard hydrocortisone test in the second patient failed to reduce the hypercalcaemia. In both patients parathyroid tumours were found at operation. It is suggested that both patients had tertiary hyperparathyroidism in which the normally tell-tale hypercalcaemia was at first masked by the other abnormalities, and that this masking may account for some cases reported as having normocalcaemic primary (or tertiary) hyperpatathyroidism. Interpretation of total plasma-calcium is likely to be unreliable unless the 25-hydroxyvitamin-D levels can be shown or assumed to be normal.