Late-onset non-thymomatous myasthenia gravis: Comparison with early-onset and very late-onset myasthenia gravis

ABSTRACT

Objective: To identify the clinical characteristics of patients with myasthenia gravis (MG) according to age at onset. Methods: We retrospectively recruited 227 non-thymomatous MG patients with adult onset who had been followed up for more than one year. The patients were classified based on the age of symptom onset as “early-onset MG” (EOMG,18–50 years; N=135), “late-onset MG” (LOMG, 50–64 years; N=53), and “very late-onset MG” (VLOMG, 65 years; N=39). Clinical features and serological findings were compared between these groups. Results: LOMG patients showed more frequent ocular MG (55%) and less frequent thymic hyperplasia (9%) compared to EOMG patients (31% and 38%; p=0.006 and p<0.001, respectively), and no female preponderance compared to VLOMG patients (female, 49% vs.77%; p=0.014). However, there were no significant differences between VLOMG and EOMG patients, except for more frequent thymic hyperplasia (p<0.001) in EOMG patients. When analyzing female patients only, less frequent secondary generalization (10%) were additionally found in LOMG patients, compared to EOMG (47%, p= 0.008) and VLOMG (59%, p=0.004) patients. Anti-acetylcholine receptor antibody (HR, 5.48; 95% CI, 1.73–17.37; p=0.004) was independently associated with secondary generalization in female EOMG patients. Conclusion: Our study suggests that LOMG patients, especially female, were characterized by frequent ocular MG and less frequent secondary generalization, distinguished from EOMG and VLOMG patients. Further large epidemiologic studies in Korea are needed to determine the characteristics of MG patients according to the age at onset and gender.