LAUSR

A 12yearold girl was referred to our clinic with left eye deviation and double vision for 10 days. She had juvenile hyperthyroidism with positive TRAb and TPOAb, and was treated with methimazole and propranolol. A local clinic diagnosed her with restrictive strabismus caused by thyroidassociated ophthalmopathy (TAO). Her visual acuity was 20/20 in both eyes, and had 6PD in horizontal deviation and 20PD in vertical. There were significant limitations in terms of downward movement, adduction and abduction of the left eye, and no conjunctival hyperaemia or chemosis was found. An MRI showed no abnormalities with extraocular muscles; she had no other additional symptoms of concern. We were concerned about a provisional diagnosis of ocular myasthenia gravis (OMG), especially after a positive neostigmine test. A positive test for antiacetylcholine receptor antibodies confirmed our diagnosis. The patient was treated with pyridostigmine and prednisone, strabismus and diplopia disappeared during followup (figure 1). Autoimmune thyroid disease and myasthenia gravis (MG) are a group of heterogeneous diseases resulting from the loss of immune tolerance to autoantigens. Studies have shown increased prevalence of cooccurrence of both due to crossimmune epitopes or autoantigens. 2 Patients with MG present with fatigue, ptosis, strabismus, difficulty swallowing and dyspnoea, aggravated after fatigue and alleviated after rest; and up to 10% have isolated eye signs which can be more unilateral. TAO, however, causes inflammation and fibrosis of orbital fat and muscles, causing periorbital soft tissue inflammation, proptosis, eyelid retraction and strabismus. Although cooccurrence of TAO and OMG is less common, they share similar symptoms such as strabismus, which can be easily misinterpreted. They can be distinguished by clinical manifestations, MRI, electrophysiology and neostigmine test. Thus, the importance of a thorough medical evaluation should not be overlooked.