Anti-AChR antibody test

The anti-acetylcholine receptor antibody test is specific for myasthenia gravis. Anti-ACh receptor (AChR) antibodies are measured by an immunoprecipitation assay in which AChR is labelled with iodine alpha-bungarotoxin, a snake venom which binds specifically to AChR, and incubated with serum

• antibody titre is raised in 85% of patients with generalised disease and in approximately 50% of those with the ocular form.

On an individual level, there is a good correlation between the antibody titre and the severity of the disease but the relationship does not apply generally, presumably because of antibody heterogeneity.

Patients negative for this test but suspected of myasthenia on clinical grounds should be tested for antibodies to other determinants of neuromuscular junction function.

• vast majority of patients with generalized myasthenia gravis (approx 85%) and pure ocular myasthenia gravis (approx 50%) will have antibodies to the skeletal muscle nicotinic acetylcholine receptor (AChR)
  • additionally 8%-10% of patients with generalized disease have antibodies to muscle-specific tyrosine kinase receptor (MuSK), an enzyme involved in acetylcholine receptor clustering in the synaptic cleft

Reference:

• Jeffrey M. Statland, Emma Ciafaloni. Myasthenia gravis: Five new things Neurol Clin Pract. 2013 April; 3(2): 126-133.