Positive acetylcholine receptor antibody in nonmyasthenic patients

Introduction/Aims In this study we aimed to determine the frequency of acetylcholine receptor (AChR) binding antibody positivity via neuroautoimmunity panel testing, and describe its occurrence in a group of nonmyasthenic disorders. Methods This is a retrospective analysis of patients who underwent neuroautoimmunity antibody panel testing from 2010 to 2018 at the Cleveland Clinic. Results A total of 10 855 patients received neuroautoimmunity antibody panel testing, and 224 (2.1%) patients were positive for AChR binding antibody. Fifty-eight patients with a known myasthenia gravis (MG) diagnosis and 11 patients with incomplete follow-up were excluded. Among the remaining 155 patients, 30 had newly diagnosed MG and 125 were nonmyasthenic. In 35 patients, MG was within the initial differential diagnosis based on the clinical presentation. In contrast to nonmyasthenic patients, myasthenic patients were more likely to have an initial clinical presentation raising suspicion for MG (73.3% vs 10.4%, P < .001), higher mean AChR binding antibody titer (8.2 +/- 15.6 vs 0.4 +/- 1.6 nmol/L, P = .011), and higher frequency of abnormal AChR modulating antibody (89.3% vs 23.9%, P < .001). A combination of AChR binding antibody of >0.5 nmol/L and modulating antibody of over 20% in patients with clinical suspicion of MG is virtually diagnostic of MG. A total of 31 (24.8%) nonmyasthenic patients carried coexisting autoimmune conditions. Discussion Elevated titers of AChR binding antibody can sometimes be found in nonmyasthenic patients. Combined analysis of clinical presentation, AChR binding antibody titer, and AChR-modulating antibody results can be helpful in confirming an MG diagnosis.