Tests for Juvenile Myasthenia Gravis: Comparative Diagnostic Yield and Prediction of Outcome

The clinical picture, family history, laboratory data, treatment modalities, and outcome in 27 juvenile myasthenics seen over a 25-year period are presented. Onset was after 10 years of age in the majority of patients. Half presented with ocular signs, the other half with generalized-onset myasthenia. Half of those with ocular-onset myasthenia progressed to generalized myasthenia. The female-to-male ratio was 3.5:1. Myasthenia gravis was reported in the mother of one patient. Ptosis was the most common presenting sign. It was unilateral at onset in 33% of patients and remained unilateral in 11%. Pharmacologic tests (neostigmine methylsulfate and edrophonium chloride) were positive in 92% of patients. Serology was positive in 63%, whereas repetitive nerve stimulation was positive in 33% when distal nerves were stimulated and in 66% when proximal and distal nerves were stimulated. Seropositivity tended to increase with generalization of the myasthenic process. No statistically significant difference in seropositivity was noted between males and females. Anti-striated muscle antibodies were detected in two patients, neither of whom had thymoma. The yield of repetitive stimulation increased with generalization of the myasthenic process and when proximal nerves were stimulated. No statistically significant difference was noted in the decremental response between seropositive and seronegative patients. The majority of ocular myasthenics were treated with pyridostigmine bromide monotherapy. With generalization of the myasthenic process, other modes of medical and surgical therapies were needed. All patients given corticosteroids ultimately underwent thymectomy. The mean age at presentation and the duration of symptoms at presentation were longer in thymectomized patients than in those without thymectomy. In thymectomized patients, those with thymic hyperplasia were all seropositive. A higher percentage of patients with normal thymus were in remission without medications than those with hyperplastic thymus. The English language literature on juvenile myasthenia is reviewed and compared with our data. The small number of patients and tests in this study preclude their use to demonstrate statistical significance or test statistical hypotheses. (J Child Neurol 1993;8:403-411).