TESTS FOR JUVENILE MYASTHENIA-GRAVIS - COMPARATIVE DIAGNOSTIC YIELD AND PREDICTION OF OUTCOME

The clinical picture, family history, laboratory data, treatment modal ities, and outcome in 27 juvenile myasthenics seen over a 25-year peri od are presented. Onset was after 10 years of age in the majority of p atients. Half presented with ocular signs, the other half with general ized-onset myasthenia. Half of those with ocular-onset myasthenia prog ressed to generalized myasthenia. The female-to-male ratio was 3.5:1. Myasthenia gravis was reported in the mother of one patient. Ptosis wa s the most common presenting sign. It was unilateral at onset in 33% o f patients and remained unilateral in 11%. Pharmacologic tests (neosti gmine methylsulfate and edrophonium chloride) were positive in 92% of patients. Serology was positive in 63%, whereas repetitive nerve stimu lation was positive in 33% when distal nerves were stimulated and in 6 6% when proximal and distal nerves were stimulated. Seropositivity ten ded to increase with generalization of the myasthenic process. No stat istically significant difference in seropositivity was noted between m ales and females. Anti-striated muscle antibodies were detected in two patients, neither of whom had thymoma. The yield of repetitive stimul ation increased with generalization of the myasthenic process and when proximal nerves were stimulated. No statistically significant differe nce was noted in the decremental response between seropositive and ser onegative patients. The majority of ocular myasthenics were treated wi th pyridostigmine bromide monotherapy. With generalization of the myas thenic process, other modes of medical and surgical therapies were nee ded. All patients given corticosteroids ultimately underwent thymectom y. The mean age at presentation and the duration of symptoms at presen tation were longer in thymectomized patients than in those without thy mectomy. 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 thy mus. The English language literature on juvenile myasthenia is reviewe d and compared with our data. The small number of patients and tests i n this study preclude their use to demonstrate statistical significanc e or test statistical hypotheses.