Lymphocytic infiltration in focal thyroiditis: an ultrastructural case study

In autoimmune thyroiditis, infiltrating lymphocytes play an important role in the disease process since they are known to release cytokines which can alter thyroid functions. The degree and site of lymphocytic infiltration in the thyroid gland have been used to differentiate between Hashimoto's disease and focal lymphocytic thyroiditis. Intraluminal lymphocytes have been reported to be absent in focal thyroiditis but present in Hashimoto's disease. However, we demonstrate here by transmission electron microscopy, that extrafollicular and intrafollicular lymphocytes could be present in focal lymphocytic thyroiditis. This seems to support the notion that focal lymphocytic thyroiditis could represent part of the spectrum of autoimmune thyroiditis and Hashimoto's thyroiditis.