Update on ocular myasthenia gravis in Taiwan.

Abstract

Myasthenia gravis (MG) is an autoimmune disease involving the neuromuscular junction. Autoantibodies to the acetylcholine receptor or, less frequently, to muscle-specific kinase, attack against the postsynaptic junctional proteins, resulting in fluctuating and variable weakness of muscles. Extraocular, levator palpebrae superioris, and orbicularis oculi muscles are particularly susceptible. The majority of patients with MG present with purely ocular symptoms including ptosis and diplopia initially. About half of these patients progress to generalized disease within 2 years. The prevalence of MG in Taiwan is 140 per million with male to female ratio of 0.7. The incidence rate is higher in the elderly. Several immune-related diseases such as lymphoid malignancy, diabetes, and thyroid diseases are associated with MG in the national population-based studies in Taiwan. Ice pack test, rest test, Tensilon/neostigmine test, circulating antibody measurement, and electrophysiological studies are useful diagnostic tools with variable sensitivity and specificity. For the patients with ocular MG, acetylcholinesterase inhibitors are usually the first-line treatment. Corticosteroids and immunosuppressant could provide better disease control and may reduce the risk of conversion to generalized form although there is still some controversy. A thymectomy is also beneficial for ocular MG, especially in refractory cases. The correction of ptosis and strabismus surgery could improve the visual outcome but should be performed only in stable disease.