Anti-acetylcholine receptor antibodies as a diagnostic marker for myasthenia gravis

Abstract

Background Myasthenia gravis (MG) is a common primary disorder of neuromuscular transmission, which is characterized by fluctuating weakness of a certain voluntary muscles, particularly those innervated by motor nuclei of the brain stem, that is, ocular and mastication muscles, and caused by antibodies binding to components in the neuromuscular junction. Most MG cases demonstrate elevated serum levels of acetylcholine receptor (ACh-R) antibodies, which cause partial or complete inhibition of receptor function and complement-mediated focal lysis of the postsynaptic membrane. ACh-R antibodies are detected in the serum of more than 80–90% patients with generalized MG, in ~50% with ocular myasthenia, and rarely in healthy people. Aims The aim of our study is to determine the value of anti-ACh-R antibodies in diagnosis and prognosis of MG and to evaluate their sensitivity and specificity in comparison between different types of myasthenia. Patients and methods All patients were recruited from the outpatient clinic of Mataria Teaching Hospital on their first visit to neuropsychiatry clinic with suspicious symptoms of MG within 3 months. Our study included 90 women, of whom 60 patients had clinical symptoms suspicious of MG. The patients were classified into five groups: four groups according to Osserman classification and the fifth group included the seronegative patients. Their age ranged from 20 to 30 years. There was another group, the sixth group, which included 30 age-matched healthy controls. All patients were subjected to full history taking, general examination, and neurological examination to facilitate clinical assessment and staging of the disease according to Osserman classification and detection of ACh-R antibodies (binding, modulating and blocking antibodies), prostigmine test, repetitive nerve stimulation, and single-fiber electromyography stimulation tests. Result There was no significant difference between studied groups regarding age. Moreover, we found significant differences between them and the control group regarding the levels of ACh-R antibodies (binding, blocking, and modulating antibodies), but there were no significant differences between them regarding the extent of MG. There is no correlation between the studied groups and the level of acetylcholine, except for a weak positive correlation between the Osserman class and level of blocking receptor antibodies. Receiver operating characteristic curves showed that all the three types of antibodies had poor value for discrimination between MG subgroups. Moreover, there is a significant difference between the studied groups regarding prostigmine, repetitive nerve stimulation, and single fiber electromyography tests. Conclusion ACh-R antibody levels are of major importance as a noninvasive sensitive and specific diagnostic test for different types of myasthenia. However, they had no role in predicting the prognosis of different classes of the disease.