Acetylcholine receptor antibodies in the diagnosis of myasthenia gravis. Study of 406 confirmed cases

Abstract

Antibodies against acetylcholine antibodies in the IgG fraction were determined in 342 patients with clinically confirmed generalized myasthenia gravis and in 64 patients with purely ocular myasthenia. The standard immunoprecipitation assay was used with detergent-extracted and 125I-alpha-bungarotoxin-marked human acetylcholine receptors as antibodies. 340 patients with generalized myasthenia and 29 with purely ocular myasthenia (99% and 45%, respectively) had titres above 0.5 nmol/l; two with generalized and five with ocular myasthenia had borderline levels (0.4 nmol/l). Titres below 0.4 nmol/l were obtained in patients with non-myasthenic oculomotor diseases (82) and other neuromuscular diseases (111). Abnormal titres were also obtained in five patients with malignant thymoma but no clinical myasthenia and one child with an immunoneuropathy. Using acetylcholine receptors from human eye muscles as antigen there was no difference between ocular myasthenia and myasthenia initially with ocular signs but later becoming generalized. Bungarotoxin-blocking antibodies were found in lower concentrations in 32 of 65 patients examined. Serial examinations demonstrated intra-individual but not linear correlations with myasthenic signs. Antibody determination is a useful and highly specific addition to the diagnostic armamentarium and is suitable for controlling treatment in patients severely affected by the disease.