Nonthymoma early-onset- and late-onset-generalized myasthenia gravis - A retrospective hospital-based study

Objective: Acquired myasthenia gravis (MG) is predominantly due to nicotinic acetylcholine receptor (AChR) autoantibodies (Ab). Differences between nonthymoma early-onset and late-onset MG were reported. We studied the clinical and serological characteristics of nonthymoma AChR Ab-positive-generalized MG patients. Patients and methods: Chinese AChR Ab-positive-generalized MG patients who had generalized disease for 3 years or longer were studied. Results: Among 41 such patients, 25 (61%) were female. The mean onset age was 43.5 years (range 9-78 years) and the mean follow-up duration was 7.8 years (range 3-20 years). Sixteen (39%) patients had late-onset disease (onset age >= 50 years). Compared to early-onset patients (onset age < 50 years), late-onset patients were characterized by male predominance (p = 0.002), absence of thymic lymphofollicular hyperplasia (p = 0.036), and a higher striated muscle Ab seropositivity rate (94% versus 4%, p < 0.001). Although there was no statistically significant difference in clinical severity and outcome or response to treatment between late-onset and early-onset patients, 50% and 75% of late-onset patients had moderate or severe disease at onset and worst status, respectively, compared to 28% and 52% for early-onset patients at onset and worst status, respectively. Also 63% of late-onset patients had disease progressed within first 3 years compared to only 40% of early-onset patients did. Conclusion: Nonthymoma late-onset-generalized MG patients were common among Hong Kong Chinese, with a statistically non-significant trend that it was clinically more severe than early-onset MG but with similar clinical outcome or response to treatment; > 90% of these patients were seropositive for striated muscle Ab. (c) 2007 Elsevier B.V. All rights reserved.