The prognosis of myasthenia gravis (MG) was assessed retrospectively using life table analysis in 844 patients followed up for a mean period of 5 years in 3 neurological centers in Milan, Rome and Pavia, Italy. The patients were aged from 2 to 90 years with a mean of 45 years. The onset of symptoms peaked in the young and middle age groups, and the commonest age at onset was between 20 and 39 years. The proportion of females progressively decreased with age. Sixty-two percent of patients received steroids, 30% anticholinesterase, 21% immunosuppressant drugs (azathioprine), and 66% had thymectomy. There was an inverse correlation between age at onset of symptoms and disease duration at diagnosis and complete remission of MG. Patients with symptoms for less than 1 year at diagnosis had the best outlook with 15-25% remissions by 5-10 years. Thymectomized patients had a significantly higher chance of complete remission than non-thymectomized (15% vs. 8% at 5 years). The earlier the operation, the better the chance of remission. The cumulative probability of complete remission was 1 % by 1 year, 8% by 3 years, 13% by 5 years, and 21% by 10 years. 
COMMENT. Seventeen percent of the patients in this study were less than 20 years of age at the onset of symptoms. The chance of complete remission is greater in younger patients with mild symptoms at onset and with shorter disease duration at diagnosis. The efficacy of thymectomy might be partly related to the younger age of the patients and the shorter disease duration at the time of operation.
In a series of 35 patients with juvenile myasthenia gravis reported from the Massachusetts General Hospital, Boston, MA , 21 underwent thymectomy and of these 18 (86%) showed complete or partial, type A (drug therapy discontinued) and type B (drug therapy continued) remissions. A similar response to medical therapy alone was obtained in 13 (93%) of 14 patients of this series, and the results were comparable with those observed in patients treated surgically. Drug therapy was discontinued and the remission was complete in 6 (29%) of thymectomized patients compared to 2 (14%) of the patients treated only with cholinergic drugs. Until patients may be allocated for thymectomy at random and a large control series is followed, the merits of surgical therapy cannot be assessed with certainty. Spontaneous remission is another factor that complicates the selection of MG patients for surgery.
An unusual association of early onset juvenile myasthenia gravis and premature birth is reported by Evans OB et al. . In a series of patients reported by Fukuyama Y et al. , 34 of 76 children had an early onset of juvenile myasthenia gravis.
In contrast to juvenile myasthenia gravis which generally responds to anticholinesterase medication, congenital or hereditary myasthenia is often refractory. A trial of 3,4 diaminopyridine, a drug that enhances acetylcholine release from motor nerve terminals, showed benefit and a highly significant increase in muscle strength in 16 patients treated. The drug was useful when given alone or in combination with anticholinesterase medication.