Thyroid-associated orbitopathy (TAO) is most commonly associated with Graves’ disease and usually occurs in the context of hyperthyroidism. Its presence in patients with Hashimoto thyroiditis is uncommon and often unexpected, making diagnosis challenging. Rare presentations such as this emphasize the complex overlap within autoimmune thyroid disorders and the necessity to consider TAO even in hypothyroid patients.

A 54-year-old male developed gradually progressive bilateral eye prominence accompanied by easy fatigability over several months. No symptoms associated with hyperthyroidism, such as heat intolerance, tremors, palpitations, or unexplained weight loss. On examination, the patient exhibited bilateral proptosis with full extraocular movements and no diplopia or eyelid retraction. His thyroid gland was not enlarged and showed no clinical signs suggestive of Graves’ disease. Laboratory evaluation demonstrated elevated TSH and low free T4, consistent with hypothyroidism, along with strongly positive anti-TPO antibodies. Notably, TRAb testing was also positive, despite the absence of clinical hyperthyroidism. An orbital scan was positive, supporting the presence of thyroid-associated orbital involvement. Based on the combination of ocular symptoms, hypothyroid biochemical profile, positive orbital scan, and the presence of autoantibodies typically associated with Graves’ disease, the patient was diagnosed with thyroid-associated orbitopathy occurring in the setting of Hashimoto thyroiditis, a presentation considered rare because TAO is predominantly linked to hyperthyroid Graves’ disease rather than Hashimoto thyroiditis.

TAO in Hashimoto thyroiditis is a rare and atypical manifestation of autoimmune thyroid disease. While TAO is strongly associated with Graves’ disease, occurring in roughly 25–50% of Graves patients depending on severity, its prevalence in Hashimoto thyroiditis is significantly lower, with studies suggesting rates of only 5–6%, and even fewer cases presenting with clinically significant orbitopathy. Although TRAb is classically linked to Graves’ disease, some Hashimoto patients can produce TRAb capable of stimulating orbital fibroblasts even when thyroid hormone levels remain low. This suggests that orbital autoimmunity may arise independently of thyroid hormone excess. The unusual combination of hypothyroidism, positive thyroid autoantibodies, and ocular involvement may lead clinicians to overlook TAO, resulting in delayed diagnosis. Recognizing this rare entity is essential, as early detection can help guide appropriate management and prevent progressive ocular damage.

This case demonstrates a rare presentation of thyroid-associated orbitopathy in a patient with Hashimoto thyroiditis, highlighting that TAO can occur even in hypothyroid states and in the absence of Graves’ disease.