MON-429 - Beyond Graves: Thyroid Eye Disease in Hashimoto'S Thyroiditis

Background
Thyroid eye disease (TED) is an autoimmune inflammatory disorder most commonly associated with Graves’ disease and thyrotropin receptor (TSHR) antibodies. Its occurrence in Hashimoto’s thyroiditis is uncommon but clinically significant. Recognition of TED outside the context of hyperthyroidism is essential, as delayed diagnosis may lead to progressive orbital morbidity. We report a case of active TED in a euthyroid patient with long-standing Hashimoto’s thyroiditis.
Case Presentation
A 72-year-old man with a 20-year history of Hashimoto’s thyroiditis presented with six months of progressive bilateral diplopia. He was clinically euthyroid on stable levothyroxine therapy (100 mcg daily). Thyroid function testing showed a TSH of 2.1 mIU/L (0.4–4.0), free T4 of 1.9 ng/dL (0.8–1.8), and free T3 of 3.2 pg/mL (2.3–4.2). There were also markedly elevated anti-thyroid peroxidase antibodies (487 IU/mL; < 35), thyroid-stimulating immunoglobulin (TSI) at 3.8 IU/L (≤0.55), and thyrotropin receptor antibodies (TRAb) at 4.2 IU/L ( < 1.75). Physical examination showed bilateral proptosis, periorbital edema, and restricted lateral gaze. Orbital magnetic resonance imaging demonstrated bilateral enlargement of the extraocular muscles with increased orbital adipose tissue, consistent with TED. Ophthalmologic assessment confirmed active, moderate-to-severe disease with a Clinical Activity Score of 4 out of 7. Antithyroid therapy was not indicated, given his euthyroid status. Systemic corticosteroids were deferred due to significant comorbidities, including diabetes mellitus and hypertension. He was managed conservatively with lubricating eye drops and close multidisciplinary follow-up.
Discussion
Although classically associated with Graves’ disease, TED has been reported in approximately 6% of patients with autoimmune hypothyroidism1. Elevated TSI and TRAb in this patient suggest that TSHR-mediated orbital fibroblast activation can occur independent of thyroid hormone excess2. This challenges the traditional linking of TED exclusively with hyperthyroidism and shows the central role of TSHR antibodies with orbital pathology.
Teaching points
1. TED can occur in patients with Hashimoto’s thyroiditis despite euthyroid status.
2. Elevated TSHR antibodies, rather than thyroid dysfunction, appear to drive orbital inflammation.
3. Having a high index of suspicion for TED in hypothyroid patients with ocular symptoms allows for early diagnosis and multidisciplinary management, potentially reducing disease-related morbidity.
Reference:
1. Kahaly GJ, Diana T, Kanitz M, et al. Prospective trial of functional thyrotropin receptor antibodies in Graves' disease. J Clin Endocrinol Metab. 2020;105(4):e1006–e1014.
2. Smith TJ, Hegedüs L. Graves’ disease. N Engl J Med. 2016;375(16):1552–1565.

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