Anti-acetylcholine receptor antibodies in myasthenia gravis. Part 1. Relation to clinical parameters in 250 patients.

We examined the significance of the presence or absence of anti-acetylcholine receptor (anti-AChR) antibodies in 250 myasthenia gravis (MG) patients and the relation between clinical features and anti-AChR levels. We found high anti-AChR levels in 2 out of 11 thymoma patients without MG, while 37 out of 250 MG patients had no detectable anti-AChR. The absence of these antibodies was related to purely ocular disease and to steroid therapy and/or thymectomy. Differences in anti-AChR levels did not correspond significantly to differences in disease activity when single measurements in patients were analysed. However, the results were influenced by both the presence or absence of a thymoma, the age at onset of disease and by steroid therapy. The thymic pathology and age at onset seemed to act independently. Early onset of disease was associated with high anti-AChR levels and absence of antibodies to striated muscle (anti-SM), whereas late onset was associated with low anti-AChR and the presence of anti-SM. Thymomas both have high anti-AChR and high anti-SM. The effect of steroid therapy on antibody levels was seen in all patient groups but was strongest in thymoma patients with early onset of disease.