Which antibody to test for Myasthenia Gravis (MG)?

From the Guidelines

To test for myasthenia gravis (MG), the most useful antibody test is anti-acetylcholine receptor (anti-AChR) antibody, as it has high specificity and is positive in approximately 80-90% of patients with generalized MG 1.

Key Points to Consider

• If the anti-AChR antibody test is negative, testing for anti-muscle-specific kinase (anti-MuSK) antibodies should be performed, as these are present in about 40-70% of AChR-negative MG patients 1.
• For the remaining seronegative cases, testing for anti-low-density lipoprotein receptor-related protein 4 (anti-LRP4) antibodies may be helpful, though this test is less widely available 1.
• The choice of antibody test should be guided by clinical presentation, with anti-AChR being the first-line test due to its high diagnostic yield in most MG cases.
• These antibodies target different components of the neuromuscular junction, interfering with neuromuscular transmission and causing the characteristic muscle weakness and fatigability seen in MG.

Diagnostic Approach

• The diagnostic approach for MG should include a combination of clinical evaluation, laboratory tests, and electrophysiological studies.
• The presence of anti-AChR antibody can confirm the diagnosis, but about 20% of patients with generalized myasthenia and about half of those with ocular myasthenia are seronegative 1.
• Repetitive nerve stimulation testing and single-fiber electromyography may also assist in diagnosis, with single-fiber electromyography considered the gold standard for diagnosis in many centers 1.

From the Research

Antibody Testing for Myasthenia Gravis (MG)

The following antibodies can be tested for MG:

• Acetylcholine receptor (AChR) antibodies, found in 80%-85% of patients 2, 3, 4
• Muscle-specific kinase (MuSK) antibodies, found in 5%-8% of patients 2, 3, 5, 4
• Low-density lipoprotein receptor-related protein 4 (LRP4) antibodies, found in <1% of patients 2, 3
• Other antibodies, such as:
  • Titin antibodies 2, 6
  • Ryanodine receptor antibodies 2, 6
  • Agrin antibodies 2, 6
  • Collagen Q antibodies 2
  • Kv1.4 potassium channel antibodies 2
  • Cortactin antibodies 2

Diagnostic Testing

Diagnostic testing for MG may include:

• Repetitive nerve stimulation 3
• Single fiber EMG 3
• Ice pack test 3
• Laboratory testing for autoantibodies, such as AChR, MuSK, and LRP4 antibodies 2, 6, 3, 5, 4

Treatment

Treatment for MG may include:

• Symptomatic treatment with acetylcholinesterase inhibitors 3, 5, 4
• Thymectomy 3, 5
• Immunotherapy, such as corticosteroids, oral immunosuppressants, and intravenous immunoglobulins 3, 5
• Novel treatments, such as eculizumab, efgartigimod, and ravulizumab, which have been approved for adult patients with generalized MG who are AChR-antibody positive 5