Survey of epidemiology, clinical picture and current treatments for elderly-onset (≥ 65 years) patients with myasthenia gravis in Nagano Prefecture, Japan

Background: Our previous population-based study in 1982-2001, Nagano Prefecture, Japan, showed increased numbers of patients with elderly-onset (65years) myasthenia gravis. Aim: We carried out a retrospective survey in 2002-2012 in the same area, and investigated the epidemiology, clinical picture and treatments for myasthenia gravis. Methods: Questionnaires were sent to 23 hospitals and patient records were reviewed. Patients were classified into the non-elderly-onset (15-64years, n=136) or elderly-onset (>= 65years, n=78) group. The questionnaires included details of sex, age/date of onset, initial symptoms, disease severity, association with thymoma and treatments. Post-intervention status and maximum/maintenance dose of prednisolone were investigated. Results: The rate of elderly-onset myasthenia gravis patients increased in 2002-2012 despite correction for increases in the elderly population. The ratio of Myasthenia Gravis Foundation of America classI was higher, and that of classIIb was lower, and the thymectomy rate in non-thymomatous generalized myasthenia gravis patients was lower in the elderly-onset group. There was no marked difference in the rate of intensive treatments (plasma exchange, intravenous immunoglobulin etc.) between the groups. Immunosuppressive therapies (prednisolone, calcineurin inhibitors) were applied frequently in both groups, whereas calcineurin inhibitor use rate and mean maximal dose of prednisolone were lower, and the minimum manifestation status with prednisolone <= 5mg rate was higher in the elderly-onset group. Conclusion: This study suggested that a low or moderate dose of prednisolone can be fully effective in many elderly-onset myasthenia gravis patients, and some might not require calcineurin inhibitors or thymectomy to reduce prednisolone dose.