Ocular myasthenia with thyroid associated ophthalmopathy in subclinical Graves’ disease

Abstract

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.