Ocular Aspects of Myasthenia Gravis

Jason J. S. Barton, MD, PhD, FRCPC, and Mohammad Fouladvand, MD, Human Vision and Eye movement Laboratory, Departments of Neurology and Ophthalmology, Beth Israel Deaconess Medical Center, Harvard Medical School; and the Department of Biomedical Engineering, Boston University, Boston, Massachusetts.

Semin Neurol. 2000;20(1) 

In This Article

Associated Disorders

There is an increased frequency of other autoimmune conditions with myasthenia. Examination and investigations in such patients are not complete without consideration of these potentially important issues.

Between 7-26% of patients with myasthenia gravis have thymoma,[114,115] in such patients mortality rates are higher and morbidity tends to be more severe. Thymic hyperplasia, characterized by infiltration of the thymus with lymphocytes and plasma cells, is found in as many as 65-70% of myasthenic patients.[116] All patients with myasthenia should have a computed tomography (CT) scan of the thorax looking for thymoma. The presence of antibodies directed against striated muscle are said to correlate with thymoma, but the sensitivity of such assays is only about 84% and the specificity 56-77%.[17,114,115] Assuming that 12% of patients with myasthenia have thymoma, this means that only about a third of those with a positive test have thymoma, though 97% of those with a negative test will not have it. These antibodies may be generated by an immunological cross reaction with antigens in the thymic tumour, specifically to neurofilaments containing titin epitopes. Anti-titin antibodies may be a better test, in that they supposedly have 100% specificity[115]: hence, all patients with a positive test will have thymoma, and the negative predictive value will range from 82 to 95%, depending upon the prevalence of thymoma.

Autoimmune thyroid disease is commonly associated with myasthenia. Either hyper- or hypothyroidism may precede or follow the development of myasthenia.[49,50] Twenty-five percent of those with normal levels of thyroid hormone will have antithyroid antibodies.[50] Conversely, 8% of patients with Graves' disease have antibodies against the acetylcholine receptor.[108]

Other autoimmune processes are occasionally found, including polymyositis.[117] In particular, patients with myasthenia and thymoma may be at increased risk for other autoimmune processes,[118] including rheumatoid arthritis, thyroiditis, polymyositis, pernicious anemia, and thrombocytopenia. Thymoma may also carry an increased risk of nonthymic cancers.[118] Rarer associations include Lambert-Eaton syndrome[119] and opsoclonus.[120]


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