acetylcholine receptor antibodiesmedical dictionary

<investigation>

<neurology> A test used to measure the amount of antibodies to acetylcholine receptors on nerve endings. This is a diagnostic test for myasthenia gravis. A normal value is no antibodies in the bloodstream.

Acetylcholine receptor (AChR) binding autoantibodies (i.e. Antibodies reactive with several epitopes other than the binding site for acetylcholine or alpha-bungarotoxin) are present in approximately 88% of patients with generalised myasthenia gravis, 70% of ocular myasthenia and in approximately 80% of myasthenia gravis in remission.

Although serum concentrations of AChR binding autoantibodies do not in general correlate well with severity of weakness, there is typical decrease in concentration as weakness improves with immunosuppressive therapy.

AChR blocking autoantibodies (i.e., antibodies reactive with the AChR binding site) are present in about 50% of patients with myasthenia gravis, 30% with ocular myasthenia gravis and 20% of myasthenia gravis in remission, AChR blocking autoantibodies are the only AChR autoantibodies present in about 1% of myasthenia gravis.

AChR modulating autoantibodies (i.e., autoantibodies which cross-link AChRs and cause their removal from muscle membrane surfaces) are present in more than 90% of myasthenia gravis and occasionally are the only AchR autoantibodies detectable in mild, recent onset or ocular-restricted myasthenia gravis.

Results for AChR modulating autoantibodies can be transiently false-positive due to curare-like drugs used during general anaesthesia. AChR autoantibodies of one or more types are found in at least 80% of ocular myasthenia gravis.

Although generally absent in neurological conditions other than myasthenia gravis(and consequently unlikely to cause confusion in neurodiagnosis), false-positive results for AChR autoantibodies occasionally occur in primary biliary cirrhosis, tardive dyskinesia, autoimmune thyroiditis, the elderly, amyotrophic lateral sclerosis patients treated with cobra venom and patients with thymoma in the absence of myasthenia gravis. Approximately 1% of patients with rheumatoid arthritis treated with D-penicillamine develop AChR autoantibodies and myasthenia gravis, both of which disappear when the drug is discontinued.

Babies born to ~10% of myasthenia gravis mothers have a transient neonatal form of myasthenia gravis that responds well to anticholinesterase therapy and usually remits within 1 month as maternal IgG disappears.

(29 Dec 1997)