Juvenile myasthenia gravis: a twenty-year experience

Juvenile myasthenia gravis (JMG) is an antibody-mediated autoimmune disorder of the neuromuscular junction, at the postsynaptic end plate. JMG presents with fluctuating skeletal muscle weakness and fatigue before the age of 18 years. Very frequently JMG presents with the involvement of the oculomotor muscles, with or without generalized involvement.

We performed a retrospective chart review of patients diagnosed with myasthenia in the pediatric neuromuscular clinics at UT Southwestern, between 1990 and 2010. Osserman classification and the response to therapy scale of Millichap and Dodge were used to compare each patient's severity of myasthenia and responsiveness to drugs before the surgery as a baseline and at the last visit, after thymectomy.

Fifty-eight patients were included; 29 (50%) were African American, and 34 (58.6%) were female. Age of onset was 11 months to 17 years, and 38 patients (65%) presented as generalized myasthenia gravis. Forty-nine patients (84%) were acetylcholine receptor antibody (AchR-Ab) positive. Of the 32 to undergo thymectomy, 19 subjects (59%) experienced an improved response to B level on the Myasthenia Scale of Millichap and Dodge (good improvement, both objective and subjective, but continuation of drug therapy required in the same or lower dosage) and 75% experienced a drop in Osserman classification by at least 1. Of the 8 individuals who did not show improvement after thymectomy, 4 subjects (50%) underwent repeat thymectomy. They had initially less invasive fluoroscopic or thoracoscopic procedure. Thymic hyperplasia was found in 7 patients (21%) and thymoma in 2.

Thymectomy was well tolerated by this group of children. There was clinical improvement after thymectomy in two thirds of the AchR-Ab-positive generalized myasthenia gravis patients. Thymic pathology was seen in less than one third of the patients who underwent thymectomy, with thymic hyperplasia being common. Further studies are necessary to determine whether thymectomy is indicated for all children with generalized JMG. More information about the immunologic, genetic, and molecular differences between patients may determine the best treatment for individual patients.