Introduction: Unilateral proptosis may be due to thyroid eye disease (TED) or retro-orbital tumours. TED is an autoimmune process affecting orbital and periorbital tissue, and generally occurs in patients with Graves thyrotoxicosis. A small subset of patients with TED (5%) have normal thyroid function, but TED is rarer in hypothyroid patients.
Case report: We report the case of a 57-year-old lady who initially presented to ophthalmology with diplopia. She was diagnosed with hypothyroidism 10 years ago and was on levothyroxine 75 μg daily. She reported no symptoms of hypothyroidism or thyrotoxicosis. Eye examination showed a clinical activity score of 3+, mild proptosis of the right eye (2 mm difference in Hertel exophthalmometer measurements), restricted right eye movements, diplopia and lid retraction. Left eye examination was normal. There were no other clinical signs of thyrotoxicosis. Thyroid function was normal, with TSH 1.81 mU/l, FT4 20 pmol/l and FT3 5.2 pmol/l. Anti-TPO antibodies were strongly positive (>1300 ku/l), but TBII was negative (<1.0 U/l). Thyroid ultrasound was normal. An MRI of her brain and orbits showed marked enlargement and oedema of both inferior recti and right superior oblique muscle with sparing of tendinous insertions, compatible with a diagnosis of right TED. She remains clinically and biochemically euthyroid at 9 months of follow-up, the latest TSH being 1.95 mU/l and FT4 19 pmol/l.
Conclusion: TED, although common in Graves thyrotoxicosis, has also been recognised in euthyroid and hypothyroid states. Clinically evident unilateral TED as seen in our longstanding well controlled hypothyroid patient due to Hashimotos is even rarer. This case supports the idea that opthalmopathy could be associated with any autoimmune thyroid disorder, irrespective of the nature of auto-antibodies present. We would also like to emphasise the importance of excluding retro-orbital tumours before diagnosing TED in patients presenting with unilateral eye disease.