A 39 year-old man was referred with weight loss and lethargy in 2011. On examination tremor, goitre and mild orbital oedema were present. His past medical history consisted of hypertension (ongoing treatment). Investigations: fT4: 37 pmol/l (921), TSH: 0.00 mU/l (0.204.50), Anti Thyroid Peroxidase: 242.6 U/ml (050) and TRAbs: 11.2 iu/l (01.6). Graves thyrotoxicosis with moderately active eye disease was diagnosed and he started on carbimazole and later thyroxine. Subsequently he developed vertical diplopia with discomfort. He had bilateral orbital swelling and right upward gaze and bilateral abduction were restricted. He eventually achieved a euthyroid state following total thyroidectomy. Despite initial response to intravenous methyl prednisolone his ocular symptoms worsened. MR Orbits showed enlargement of the extra-ocular muscles consistent with active thyroid disease. Orbital radiotherapy was contraindicated due to hypertension and young age and he started oral prednisolone. Rituximab was considered but not given because symptoms improved on prednisolone.
Several months later he developed right ptosis associated with progressive ocular abduction restriction, most troublesome when tired. He was biochemically euthyroid, with undetectable TRAbs and repeat orbital MR scan showed reduction in ocular muscle size. Antiacetylcholine receptor antibodies (AChRAbs) were negative and no other features of myasthenia gravis (MG) were present. In 2015 a trial of pyridostigmine was undertaken and several weeks later his abduction restriction had completely resolved. He was diagnosed with a combination of thyroid eye disease and ocular MG.
Conclusion: There is a known association between autoimmune thyroid disease and MG but their simultaneous occurrence is rare. The absence of AChRAbs does not exclude MG. Diplopia can occur in patients with Graves disease but diplopia, ptosis and restrictive ocular movements are highly suggestive of MG. The co-existence of the two conditions can present diagnostic difficulty and this case highlights the need for multispecialty input when managing patients with complex thyroid eye disease.