Characteristics of late-onset myasthenia gravis

Abstract

An increasing incidence of myasthenia gravis (MG) has been reported in the elderly, but the full clinical ramifications of late-onset myasthenia gravis (LOMG) remain unclear. We describe the clinical features of our cohort of patients with MG with an emphasis on an onset after the age of 50. This was a retrospective analysis of medical records of a cohort of patients followed in two tertiary neuromuscular clinics and comparison of early onset MG (EOMG) versus LOMG. There were 174 patients with a mean age of onset of 55.2 ± 19.1 years, and 44 % were women. Late onset of myasthenia gravis after age 50 was reported in 114 patients (66 %). Anti-AChR antibody titers were elevated in 78 % of patients (65 % with EOMG vs. 85 % with LOMG; p = 0.003), and frequency of elevated titers of anti-MuSK antibodies was similar in both groups (present in 38 % of all tested seronegative patients). Myasthenic crisis was equally common in generalized EOMG and LOMG (13 %). Ocular MG was more common in LOMG compared to EOMG (40 vs. 18 %, p = 0.021). Diabetes was more prevalent with LOMG (27 vs. 5 %; p = 0.0002). Overlapping clinical features of EOMG and LOMG are consistent with a continuous clinical spectrum of a single condition, with more frequent occurrence of seropositive and ocular MG with a late onset. A higher burden of comorbidities, such as diabetes mellitus, may warrant a modified approach to treatment of myasthenia in LOMG. However, overall disease severity may not be higher with aging. These observations have implications for design of MG clinical trials and outcomes studies.