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

Abstract 

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.

Keywords: Nonthymoma-generalized myasthenia gravis, Acetylcholine receptor autoantibodies, Late-onset myasthenia gravis, Early-onset myasthneia gravis, Striated muscle autoantibodies