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

Abstract

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.

Switching of Hashimoto Thyroiditis Into Graves’ Disease: A Case Report and Literature Review

“…Although the conversion of HT to GD is a rare phenomenon and its mechanism is still unclear, a few cases were reported in the medical literature. Table 1 provides a summary of some cases (2,4,(12)(13)(14)(15)(16)(17).…”

“…The median period of this conversion is about 12-36 months. In some cases, it was reported within decades, and most of the reported cases were middle-aged females (13).…”

“…It is still not well understood why a patient with established hypothyroidism later experiences hyperthyroidism. The most important hypothesized mechanism is the presence of different autoantibodies that includes thyroid blocking antibodies, thyroid-stimulating antibodies, and the response of the thyroid gland to these antibodies (13). Nonetheless, despite the inflammation and thyroid cell destruction because of the lymphocytic infiltration of the thyroid gland in chronic autoimmune thyroiditis (HT), there are still small numbers of functioning cells which are sufficient to respond to the stimulatory effect of TSAb in GD (17).…”

“…Although the switch from HT into GD is rare, it should be noted that it can occur at any time during the disease (13). Therefore, the authors recommend that hyperthyroidism should be considered in any patient with controlled hypothyroidism presenting with clinical and biochemical findings indicating hyperthyroidism that persists even after stopping levothyroxine.…”

The Unusual Late-Onset Graves’ Disease following Hashimoto’s Related Hypothyroidism: A Case Report and Literature Review

“…One case had positive TSAb, however, without developing hyperthyroidism. Our literature search otherwise revealed additional individual case reports [ 8 , 10 – 16 ]. Kamath et al in 2012 suggested a role for the immunological shift as a possible mechanism, concluding that this theory remains only speculative at this stage [ 8 ].…”