Development of Grave's disease seven months after Hashimoto's thyroiditis: a rare occurrence

Hashimoto's thyroiditis (HT) and Graves' disease (GD) are two opposite poles in the spectrum of autoimmune thyroid disease. On one extreme, HT or Chronic Lymphocytic thyroiditis (CLT) courses, as its name implies, with lymphocytic infiltrates replacing thyroid follicles, resulting in a loss of hormone-producing cells and, thus, primary hypothyroidism. On the other extreme, GD is characterized by primary hyperthyroidism due to stimulating autoantibodies against thyroid-stimulating hormone receptors (TSHRs) localized on thyrocytes' membranes of intact thyroid follicles. The presence of HT after GD or the concomitant combination of these two autoimmune entities ending in HT-depending hypothyroid state is well known. However, occurrence of GD after primary hypothyroidism due to CLT is very rare since thyrocytes with their TSHRs are promptly lost. We report a case in which hyperthyroidism occurred seven months after presentation of primary hypothyroidism and discuss potential mechanisms involved.