Simultaneous ocular myasthenia gravis and thyroid eye disease: beware

Thyroid eye disease (TED) is an autoimmune disease that is usually seen in patients with Graves’ thyrotoxicosis although it can also be seen in hypothyroid as well as euthyroid patients. Myasthenia gravis (MG) is also an autoimmune antibody mediated disorder characterized by fluctuating weakness of the skeletal muscles that can occur with TED.

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MG is due to impaired neuromuscular transmission due to circulating anti-acetylcholine receptor antibodies (AchRAb). MG has a high incidence of association with other autoimmune diseases including Graves’ disease and autoimmune thyroiditis. It has been found that about 40% of people with ocular myasthenia gravis have anti-thyroid antibodies.^{1, 2}

The most common lid feature of TED is lid retraction while that of ocular MG is ptosis.³

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Thus, patients with ocular MG who present with lid retraction or TED who present with ptosis should be considered to have both disorders until proven otherwise.

Case report

A 67-year-old white female presented with a 2 year history of binocular horizontal diplopia, bilateral ptosis, Cogan’s lid twitch and orbicularis weakness. She was diagnosed with ocular MG and had positive acetylcholine receptor antibodies.

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She started oral pyridostigmine which modestly helped with her symptoms. She never developed any systemic weakness or generalized MG. A CT scan of the chest was negative for thymoma. She returned to the neuro-ophthalmology clinic with a new complaint of eyelid retraction of her left eye (OS). At the time of her prior evaluation she had bilateral ptosis.

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