Focal lymphocytic infiltration in thyroids of elderly people. Histopathological and immunohistochemical studies.

Histopathological studies were made on the thyroid glands obtained from 169 autopsy cases of patients, ranging in age from 63 to 97 years, who had not had collagen diseases. Focal lymphocytic infiltration was found in 29 (17.2%) of 169 thyroid glands. Although the relationship between the incidence and age was unclear among elderly people, there was a tendency of a prevalence in females with respect to severity of focal lymphocytic infiltration. Immunohistochemically, a predominance of T cells (80-90%) was found in the thyroid lesions. The infiltrating T cells were composed of chiefly OKT 4+ or Leu 3a+ subset (60-80%) and lesser number of OKT 8+ or Leu 2a+ subset (20-40%). An increase in the percentage of OKT 8+ or Leu 2a+ cells, however, was observed in the tiny lesions infiltrating the interfollicular connective tissues. In aged patients over 63 years old, the average weight of thyroid glands without lymphocytic infiltration, obtained from female patients, was approximately 11 g, and the average weight of those with focal lymphocytic infiltration was approximately 17 g, whereas there was no significant difference in the weight of thyroid glands obtained from male patients with and without focal lymphocytic infiltration (14 g). The findings in the present study suggest that focal lymphocytic infiltration in thyroid glands is a focal sign of an immunological disorder which is based on autoimmunity associated with aging.