Ocular myasthenia with thyroid associated ophthalmopathy in subclinical Graves’ disease

Ocular myasthenia in Graves’ disease is very rare with less than 10 cases reported. We present a clinically euthyroid lady with features of thyroid associated opthalmopathy (TAO) who had mild ptosis, external opthalmoplegia, firm goiter and subclinical hyperthyroidism. Hertel exopthalmometry confirmed exopthalmos. CT orbit revealed thickening of bilateral inferior, medial and superior recti. Anti-thyroid peroxidase antibody was positive (154IU/ml; normal<40IU/ml). Repetitive nerve stimulation test (RNST) of bilateral nasalis muscle showed decremental reponse, more prominent on the left side. Electrodiagnostic screening for concomitant myopathy or neuropathy was unremarkable. A subsequent positive neostigmine test and a positive anti-acetylcholine receptor antibody (1.46nmol/L; normal<0.5nmol/L) lead to the diagnosis of ocular myasthenia with TAO and subclinical Graves’ disease. Ptosis and ophtalmoplegia improved with pyridostigmine and carbimazole.. She was doing well even after 2 years of follow up. Any patient of TAO with ptosis and disproportionate opthalmoplegia should be evaluated to rule out ocular myasthenia. The idea of presenting this case is to highlight that TAO and ocular myasthenia can co-exist and one has to always keep a strong clinical suspicion, as lack of treatment of even clinically silent Graves’ disease in a patient with myasthenia can aggravate the weakness.