Endocrine Abstracts

TSH receptor antibodies (TRAb) are autoantibodies directed against the TSH receptor, predominantly located on the thyroid epithelial cell surface. Two types of TSH receptor antibody have been found to exist in patients with autoimmune thyroid disease: thyroid stimulating antibodies (TSAb) and TSH-stimulation blocking antibodies (TSBAb). It has generally been felt that patients with positive TSAbs develop Graves’ hyperthyroidism and those with TSBAb antibodies develop hypothyroidism and there is no co-existent antibody state. Whilst rare, several case reports have highlighted however that a switch from TSAb to TSBAb predominance (and vice versa) can occur and consequently result in oscillation between clinical and biochemical hyper- and hypothyroidism.

We present the chronological events, including clinical history and biochemical results of 3 patients with fluctuating thyroid status and correlate this with the history of therapeutic interventions for their thyroid disease. All 3 patients had positive TRAb antibodies and similarly to other case reports in the literature, were all women and had comparable characteristics to other patients with autoimmune thyroid disease.

Studies have shown that in cases where there is a simultaneous presence of TSAb and TSBAb in vivo, the subsequent clinical state of the patient can be correlated with the relative concentrations and affinities of these antibodies at any one time. A recent review discusses the potential mechanisms involved in this immunological and clinical thyroid switching including the impact of levothyroxine, anti-thyroid drugs and physiological states such as pregnancy on thyroid status. We discuss the importance of this rare phenomenon including the need for careful patient monitoring and the implications for prognosis and options for definitive management.