Invited Commentary

Abstract

Juvenile myasthenia gravis (JMG) is a form of MG presenting before age 19 years and more common in Asian populations. The report from Cheng and colleagues [1Cheng C. Liu Z. Xu F. et al.Clinical outcome of juvenile myasthenia gravis after extended transsternal thymectomy in a Chinese cohort.Ann Thorac Surg. 2013; 95: 1035-1042Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar] is a retrospective analysis of 141 patients who underwent extended transsternal thymectomy in a Chinese hospital. The objective of the report was to identify factors associated with complete or pharmacologic remission, which occurred in approximately 46% of patients. The authors found that older age at operation (> 12 years) and a short waiting time from diagnosis (< 12 months) were associated with higher rates of complete remission. Approximately 70% of patients presented with ocular MG (OMG), a figure in line with the epidemiology of prepubertal JMG. In this pediatric population, OMG has been shown to have a higher rate of spontaneous remission and very low rate of progression to generalized MG compared with adults, in whom 80% of OMG will progress to generalized MG. Thymectomy remains a controversial treatment for JMG. On the one hand, thymectomy is justified in refractory cases because patients may be dependent on long-term immunosuppressant medications, with the resultant side effects, and because persistent amblyopia can result in children. On the other hand, thymectomy is not proven to reduce the risk of progression to generalized MG and caution needs to be taken in early childhood due to subsequent immunosuppression and high rates of spontaneous remission. The authors did not assess separately the outcome of patients with OMG and of those with generalized MG. Interestingly, older patients responded better to extended transsternal thymectomy, and this may be because they behave more similarly to adult MG patients. Nearly 50% of JMG patients are known to present without acetylcholine receptor antibody. A variable percentage of them (0% to 49%) have antibodies against another neuromuscular junction protein, muscle-specific kinase, which is associated with more generalized disease. Current evidence suggests that thymectomy is not recommended in muscle-specific kinase–positive disease because it is unclear whether thymectomy confers any benefit. Unfortunately, serology was not evaluated in this series, which would have contributed to a better understanding of the role of thymectomy in childhood. The use of corticosteroids was associated negatively with outcome in OMG. Because patients with refractory and more severe OMG had received corticosteroids, this result may be flawed by selection bias. A propensity score case-matched analysis between patients with and without steroids would have minimized this problem. The authors should be commended for analyzing the largest series of JMG ever reported in the literature and contributing to raise the interest for this pediatric disease in our community.