Plasma cell granuloma of the thyroid: report of case and review of literature.

Objective: To report the 12th case of a patient with a plasma cell granuloma of the thyroid, a rare cause of goiter and hypothyroidism.

Methods: We present a case report of a woman with a plasma cell granuloma of the thyroid. The clinical and pathologic features of the lesion are described, the differential diagnosis is discussed, and the relevant literature is reviewed.

Results: Plasma cell granulomas are uncommon benign lesions most typically located in the lung and only rarely identified in other organs. Only 11 cases of plasma cell granuloma of the thyroid gland have been reported previously. We describe the case of a 55-year-old woman with a long history of hypothyroidism and compressive symptoms from an enlarging neck mass. A thyroidectomy was performed. On gross examination, the thyroid had been replaced by firm, white, fibrotic tissue with a multinodular appearance. On microscopy, the infiltrate consisted predominantly of plasma cells that were polyclonal with the expression of both kappa and lambda light chains. A minor component of CD5- and CD20-positive (T and B) lymphocytes was observed. These features were important for establishing the diagnosis of a plasma cell granuloma and distinguishing the lesion from a plasmacytoma.

Conclusion: This is the 12th reported case of plasma cell granuloma of the thyroid gland, a very rare cause of either a diffuse or a nodular goiter and hypothyroidism. The presence of a polyclonal plasma cell population with the expression of both kappa and lambda light chains helps to distinguish a plasma cell granuloma from a malignant plasmacytoma of the thyroid gland.