To report a case of ocular myasthenia gravis in conjunction with thyroid-associated ophthalmopathy in a patient who showed incomitant strabismus and blepharoptosis as well as to discuss the clinical features and tests that may help distinguish these 2 diseases.

A 46-year-old man without any previous history of systemic and ophthalmic disease presented with binocular diplopia that occured a month earlier. The patient had no other systemic symptoms except a 7 kg weight loss within the last month. The patient was referred to the department of internal medicine and brain magnetic resonance imaging was performed to ascertain the cause of suspected left superior oblique muscle palsy. The patient was diagnosed with Graves' disease and underwent medical treatment. One month later, the patient presented with consistent diplopia and exophthalmos and showed a swelling of eyelid and ptosis in the right eye. Intravenous high-dose steroid therapy was administered to the patient. After the treatment, symptoms of diplopia and lid swelling were improved, however ptosis persisted. Ocular myasthenia gravis was suspected and various tests were conducted. Anti-acetylcholine receptor antibodies were detected in large amounts and ptosis was improved dramatically by an administration of an anticholinesterase agent. The patient was diagnosed with ocular myasthenia gravis in conjunction with thyroid-associated ophthalmopathy.

Ocular myasthenia gravis should be suspected in patients with thyroid-associated ophthalmopathy who have signs or symptoms of ptosis.