Parasitic nodule of the thyroid in a patient with Graves' disease.

We report a case of a parasitic nodule of the thyroid in a patient with Graves' disease, which mimicked a lymph node metastasis from a primary occult thyroid carcinoma. The patient was a 67-year-old Japanese woman with a past history of subtotal thyroidectomy for Graves' disease, who was referred to our hospital because of a right cervical mass. A lymph node-like lesion measuring 1.5 cm in diameter was palpable, distinct from the remnant of the right thyroid lobe. Thyroid scintigraphy using 123I-Na revealed a hot lesion at the upper lateral portion of the right thyroid lobe, and this was resected. Microscopically, the mass showed thyroid follicles with lymphocytic infiltration and lymphoid follicles. Clear ground glass nuclei, nuclear grooving and intranuclear inclusions were not observed. No morphological evidence of the lymph node was found in the mass by reticulin staining. Parasitic nodules of the thyroid in patients with Graves' disease may mimic a metastatic carcinoma of the thyroid.