Small cell medullary thyroid carcinoma: A diagnostic dilemma.

Small cell variant of medullary thyroid carcinoma (MTC) is a rare variant. In the past, primary thyroid lymphomas were thought to be small cell MTC (SCMTC). However, with the advent of immunohistochemistry, it was realized that SCMTC is rare. Our patient presented with neck mass for 1 year with an outside laboratory report of neoplastic lesion. His serum calcitonin levels were normal, but serum carcinoembryonic antigen (CEA) levels were high. He underwent total thyroidectomy and was diagnosed to have small cell variant of MTC. Immunohistochemistry for AE1/AE3 and CEA were positive while calcitonin was negative. The patient underwent radiotherapy but developed metastasis 3 months later. Thus, SCMTC is a rare and aggressive variant of MTC. In the absence of raised serum calcitonin levels, raised serum CEA levels are helpful. It is necessary to identify this rare variant as it connotes a poor prognosis and should be treated aggressively.