Postpartum thyroiditis. A clinical, histologic, and immunopathologic study of 15 cases

Fifteen specimens from 15 patients with clinically and laboratory-proven postpartum thyroiditis were examined histologically; 8 specimens were obtained during the hypothyroid phase and the other 7 during the recovery euthyroid phase. All specimens showed focal or diffuse chronic thyroiditis. In the eight specimens taken during the hypothyroid phase and four specimens during the early recovery phase, follicular disruption and hyperplastic change of the follicle were common and characteristic histologic features. In the three specimens taken during the late recovery phase, only focal infiltration of lymphocytes was observed. This histologic change resembled that in spontaneous silent thyroiditis, as shown in the authors' previous study. The authors believe that postpartum thyroiditis and spontaneous silent thyroiditis may fit the same category clinically and histologically. In addition to performing the histologic examination, the authors examined the intrathyroidal lymphocyte subsets and HLA-DR antigen expression in the follicular cells immunohistochemically and compared them with those in chronic thyroiditis (usual type). In postpartum thyroiditis, a significant increase of helper-T-cell numbers and increased expression of HLA-DR antigen in the follicular cells were observed, suggesting an enhancement of autoimmune reactivity.