C-cell hyperplasia developing in residual thyroid following resection for sporadic medullary carcinoma

Four days following resection of a medullary carcinoma of the thyroid, a 49-year-old man experienced elevated serum calcitonin levels. There was no evidence of metastasis. A re-exploration of the patient's neck demonstrated a histologically normal thyroid remnant that demonstrated C-cell hyperplasia by immunoperoxidase staining. The lack of a familial history, a normal parathyroid, and the absence of C-cell hyperplasia in non-tumorous thyroid of the original resection support the concept that the patient had a sporadic tumor. Patients who had undergone incomplete thyroidectomies for non-familial disease are at risk for developing C-cell proliferation and possibly medullary carcinoma. We conclude that the C-cell hyperplasia in this thyroid remnant is the source of the elevated calcitonin level; this mechanism may also explain postoperatively elevated calcitonin levels in some patients with medullary carcinoma treated by partial thyroidectomy and high calcitonin levels for a variable period after complete thyroidectomy.