Background: Anti-acetylcholine receptor antibody (AchRab) plays an important role in the pathogenesis of myasthenia gravis (MG). The purpose of this study was to evaluate the clinical characteristics and long-term changes of anti-acetylcholine receptor antibodies in patients with juvenile MG.

Methods: The data from 77 patients with juvenile MG, aged from 3 months to 16 years (45 were female and 32 male with a female to male ratio of 1.4:1) treated at Children’s Hospital, Fudan University from 1992 to 2002 were reviewed retrospectively. All the patients were confirmed clinically and by the neostigmine test. Information about mode of MG presentation, myasthenia, ocular and systemic involvement, AchRab level, therapy and outcome was collected and evaluated. The serological test was done during follow-up.

Results: The onset of MG occurred at age below 3 years. The extraocular muscles were most frequently involved. According to the modified Osserman’s criteria, 54 patients (70%) were classified into type I, 21 (27%) type II, and 2 (3%) type III. Of 52 patients, 18 (35%) were positive for AchRab and 16 (31%) were positive for acetylcholine premembrane receptor antibodies. The clinical state of the patients was not clearly correlated with the levels of the antibodies. No significant difference was observed between clinical type and AchRab positive among the 3 groups. Two (11%) of 18 patients were positive for thymona associated antibody (Titinab). Serological test during follow-up showed that 6 (60%) of 10 AchRab seronegative patients turned to be AchRab seropositive. In 85% of the patients, cluster of differentiation (CD) cells were abnormal, most of them showed reduced levels of CD4+ or CD3+ and CD8+. Thymus proliferation was found in 22 patients (42%) by CT and thymoma was confirmed operatively in 2 (4%). In 50% of the patients, electromyography (EMG) showed nothing abnormal. After administration of anticholinesterase drugs and steroids, the prognosis of the patients with MG was fairly good.

Conclusions: The age of onset of MG is younger, and the incidence of type II MG is increased. AchRab seronegative patients could turn to be positive. Serological monitoring is helpful to find more AchRab seropositive cases. Steroids have been proven effective and safe in treatment of juvenile MG. Methylprednisolone may produce less side-effects than oral predisone after steroid therapy.