Thyroid carcinoma found at parathyroidectomy: Association with primary, secondary, and tertiary hyperparathyroidism

BACKGROUND. Frequent reports of an association between primary hyperparathyroidism (HPT) and well differentiated thyroid carcinoma, compared with the few reports of associated secondary HPT and thyroid carcinoma, may have implications for different etiologic relationships between the conditions. METHODS. A retrospective review was performed of patients who underwent surgery for HPT between 1975 and 1996 in a single institution. The prevalence of well differentiated thyroid carcinoma diagnosed at the time of parathyroidectomy (PTX) was compared for patients with primary, secondary, or tertiary HPT. RESULTS. There were 845 operations for HPT in 824 patients. Twenty-two patients were found to have thyroid carcinoma at the time of PTX. Thyroid carcinoma was found in 2.6% of the patients with primary and 3.2% of the patients with either secondary or tertiary HPT (P = 0.550). Twenty-one of the patients had papillary carcinoma and 1 had a follicular carcinoma. Eighteen of the carcinomas were < 1 cm in size. A prior history of head and neck irradiation was associated with the diagnosis of thyroid carcinoma at the time of PTX (P < 0.001). Neither renal failure, organ transplantation, female gender, lymphocytic infiltration, nor follicular adenoma of the adjacent thyroid were significant in the association between HPT and thyroid carcinoma. CONCLUSIONS. These data suggest that the association between thyroid carcinoma and HPT is coincidental and possibly related to the closer surveillance of the thyroid gland due to PTX and often concomitant removal of thyroid tissue. Patients with HPT and a history of head and neck irradiation are at increased risk of thyroid carcinoma.