Hyperparathyroidism unmasked by the treatment of hypothyroidism secondary to Hashimoto's thyroiditis.

Primary hyperparathyroidism masked by untreated hypothyroidism was first noted by Kissin and Bakst in 1947; since then there has been only a single case reported. As a result, it has been thought to be a rare complex of parathyroid disease. During the past 17 years we observed 17 patients who developed primary hyperparathyroidism after their treatment for hypothyroidism (secondary to Hashimoto's thyroiditis) with thyroxine had been well underway. The patients were all women whose ages ranged between 16 and 76 years. The clinical and biochemical manifestations of hyperparathyroidism were noted 2 months to 30 years after thyroxine therapy. All patients underwent standard subtotal parathyroidectomy. Fourteen patients had a single parathyroid adenoma and three had multiglandular adenomatous hyperplasia. It is of interest that all 17 patients were found to have Hashimoto's thyroiditis, based on antimicrosomal antibody titers or histopathologic criteria. Thus we present a series of patients who developed primary hyperparathyroidism in a background of Hashimoto's thyroiditis and hypothyroidism treated with thyroxine. We are intrigued by the association of hyperparathyroidism and Hashimoto's chronic thyroiditis. From this experience it seems appropriate to evaluate parathyroid function in patients with hypothyroidism secondary to Hashimoto's thyroiditis before the initiation of treatment with thyroxine and at intervals thereafter.