Endocrine Abstracts

Introduction: Thyroid eye disease (TED) is the major extra-thyroidal manifestation of Graves’ disease (GD). The delayed onset of TED after hyperthyroidism resolution and the decline in TRAb levels is a rare occurrence, necessitating the exclusion of other underlying orbital inflammatory diseases.

Case Report: A 59-year-old non-smoking female patient presented with thyrotoxicosis symptoms (fatigue, palpitations, resting tremors) persisting for three months, along with a homogeneous elastic goiter and no orbital abnormalities. Laboratory investigations revealed primary hyperthyroidism (TSH<0.01 mIU/l; FT4= 38.7 pmol/l, 1.8xULN), with positive TRAb at 9 IU/ml (3xULN), strongly indicating GD. The patient was treated with methimazole 7.5 mg/day for 11 months, resulting in clinical improvement, normalization of thyroid function, and a decrease in TRAb levels to 3.59 IU/ml. In the 12th month of treatment, bilateral exophthalmos, eyelid retraction, and bilateral diplopia, predominantly affecting the left eye, emerged. The orbitopathy was inactive (activity score 2/7) but severe. Given the favorable clinical, biochemical, and serological evolution of GD, and the absence of smoking, we aimed to exclude underlying orbital inflammatory disease. Immunological investigations ruled out IgG4-related disease and granulomatosis with polyangiitis. Orbital MRI revealed bilateral fusiform swelling with abnormal signal and intense enhancement of the extraocular muscles. Inflammation was primarily located in the left inferior rectus muscle. The insertions of the extraocular muscles on the eyeballs were spared, ruling out idiopathic orbital myositis (IOM). Delayed-onset TED was confirmed, and the patient continued methimazole treatment with a high-dose corticosteroid regimen (6 weekly boluses of 750 mg of methylprednisolone), leading to the resolution of the patient’s diplopia.

Discussion: TED is the most common orbital inflammatory condition. Its delayed onset is rare, occurring in 7% of non-smokers and 20% of smoking individuals with GD. Its primary differential diagnosis is IOM. The distinctive features of TED include the presence of thyroid dysfunction, positive TRAb, painless bilateral involvement, and preservation of extraocular muscle insertions on the eyeballs.

References: 1. Suzuki, Nami, et al. "Clinical course of thyroid function and thyroid associated-ophthalmopathy in patients with euthyroid Graves’ disease." Clinical Ophthalmology (2018): 739-746. 2. Marinò, M., et al. "Orbital diseases mimicking graves’ orbitopathy: a long-standing challenge in differential diagnosis." Journal of Endocrinological Investigation 43 (2020): 401-411.