Hypothyroidism to hyperthyroidism: an immunological pendulum swing from two extreme poles - a case series.

We report two women who were diagnosed with hypothyroidism due to what was thought to be Hashimoto's thyroiditis 18 and 16 years ago, respectively. They had been euthyroid on stable doses of levothyroxine for many years, and they presented to our clinic with clinically and biochemically overt hyperthyroidism that persisted even after stopping levothyroxine. Immunological and imaging workups were consistent with Graves' disease. Both patients were treated medically and then received definitive treatment. To our knowledge, the intervals for these two conversions are among the longest conversion intervals reported in the medical literature.