7058 Debunking the Bimodal Theory of Autoimmunity: Graves' Disease (GD) Hyperthyroidism and Hashimoto’s Disease (HD) Hypothyroidism Can Coexist on a Spectrum, a Case Series

Abstract Disclosure: A. Atri-Schuller: None. A.C. Zuzek: None. A. Yaqub: None. It is not uncommon for hyperthyroid patients to eventually become hypothyroid after prolonged periods of inflammation and hyperactivity, occasionally referred to as “burnt-out Graves.” However, going from a hypothyroid to a hyperthyroid state has been described as a rare phenomenon in the literature. In this abstract, we present three patients who have been on both ends of the hypo-to-hyperthyroid spectrum, and we suggest a potential pathophysiologic basis for such transition.The patients all had thyroid antibody positivity for TPO (typically positive in HD), TSI and TRAb (typically positive in GD). The first patient presented with hyperthyroidism, was clinically hypothyroid and then back to hyperthyroid. The second patient presented with hypothyroidism, then became hyperthyroid, then hypothyroid, then hyperthyroid again. The third patient, the youngest, was initially hypothyroid, then euthyroid, and is now hyperthyroid. Interestingly, the first two patients had coexisting autoimmune conditions: cutaneous lupus and antibodies suggestive of Sjorgen’s syndrome in the first patient, and lupus in the second patient. The third patient, the youngest, does not have another diagnosed autoimmune condition at this point. All three cases support the hypothesis that autoimmune thyroid disease can coexist on a spectrum. Our abstract proposes that the transformation from HD to GD can be explained in the context of the spectrum of autoimmunity based on the following theories: 1. Individuals can have more than one autoimmune disorder; the clinical condition that manifests may be related to the antibodies that predominate at a time 2. The factors that cause a switch in the predominance of antibodies remains largely unknown, but may include pregnancy, LT4 hormone replacement, anti-thyroid drugs, monoclonal antibodies, immunosuppression and in rare cases neck irradiation. 3. A high index of suspicion from the clinician is warranted when the hypothyroid patient starts requiring lower doses of hormone replacement, and if transformation is suspected we recommend checking both TSH receptor and TPO antibodies. In very rare cases, patients have been observed to spontaneously oscillate from hypo to hyperthyroid and vice-versa despite appropriate treatment, in which case definitive therapy is recommended. There are still unanswered questions regarding the use of antibody testing in autoimmune thyroid diseases. For example, does the degree of antibody positivity correlate with clinical disease burden? This would be helpful to know in patients with a history of both hyper and hypothyroidism as it would help determine which part of the hypo-to-hyperthyroid spectrum the patient is on and on which direction of the spectrum they are heading. It would also be interesting to determine if a flare of a coexisting autoimmune disorder could push the patient from one end of the spectrum to the other. Presentation: 6/3/2024