Development of generalized disease at 2 years in patients with ocular myasthenia gravis. Kupersmith MJ, Latkany R, Homel P. Arch Neurol 2003;60:243–248

Abstract

The initial symptoms or signs of myasthenia gravis (MG) are ptosis, extraocular muscle weakness, or ocular misalignment in up to 65% of patients. Clinically apparent generalized disease develops in more than 50% of patients who present with ocular MG, typically within 2 years. The optimal treatment of ocular MG, including the use of corticosteroids, remains controversial. In addition, the prevalence of thymoma and the optimal performance of the edrophonium chloride test for ocular myasthenia remain unknown. The goal of this study was to assess the effect of oral corticosteroid therapy on the frequency of development of generalized MG within 2 years, the incidence of thymoma, and the amount of edrophonium needed for a positive test result in patients with ocular MG. The authors reviewed an MG database of 147 patients. Patients underwent measurement of acetylcholine receptor (AChR) antibody levels and chest computed tomography. Unless contraindicated, patients with diplopia were recommended for therapy with prednisone, up to 40 to 60 mg/day, with the dosage tapered for 5 to 6 weeks. Most continued to receive daily or alternate-day doses of 2.5 to 10 mg to prevent diplopia. Patients not given prednisone (untreated group) received pyridostigmine bromide or no medication. After the diagnosis, the authors documented the signs and symptoms of ocular and generalized myasthenia gravis and performed 2-year follow-up in 94 patients. The mean dose of edrophonium chloride to give a positive response was 3.3 mg (standard deviation, 1.6 mg) for ptosis and 2.6 mg standard deviation, 1.1 mg) for ocular motor dysfunction. Thymoma was diagnosed in 1 patient (0.7%). Generalized MG developed within 2 years in 4 of 58 treated and 13 of 36 untreated patients. The odds ratio (OR) for development of generalized disease in the treated group was 0.13 (95% confidence interval [CI], 0.04–0.45) compared with the untreated group. The AChR antibody level was not predictive of development of generalized MG at 2 years, but the risk was greater in patients with abnormal AChR antibody levels (OR, 6.33; 95% CI, 1.71–23.42). Logistic regression that included age, abnormal AChR antibody level, and prednisone therapy yielded significance only for abnormal AChR antibody level (OR, 7.03; 95% CI, 1.35–36.64) and treatment (OR, 0.06; 95% CI, 0.01–0.30). The authors conclude that at 2 years, prednisone treatment appears to reduce the incidence of generalized MG to 7% in contrast to 36% of patients who did not receive prednisone. Thymoma, although uncommon, may occur in ocular myasthenia gravis. Only small amounts of edrophonium are needed to diagnose ocular myasthenia gravis.—Valérie Biousse