What laboratory tests are indicated to diagnose Myasthenia Gravis (MG)?

From the Guidelines

To diagnose Myasthenia Gravis (MG), I recommend ordering acetylcholine receptor (AChR) antibody tests, including binding, blocking, and modulating AChR antibodies, as the first-line laboratory evaluation, as supported by the most recent study 1. The diagnosis of MG involves a combination of clinical evaluation and laboratory tests. The following laboratory tests are indicated:

• AChR antibody tests, which have high sensitivity (80-85%) for the condition 1
• If AChR antibodies are negative, consider ordering anti-muscle-specific kinase (MuSK) antibodies, which are positive in about 40% of AChR-negative cases 1
• For patients negative for both AChR and MuSK antibodies, testing for low-density lipoprotein receptor-related protein 4 (LRP4) antibodies may be helpful 1
• Anti-striated muscle antibodies can support the diagnosis, particularly in thymoma-associated myasthenia gravis 1
• Electrodiagnostic studies, including neuromuscular junction testing with repetitive stimulation and/or jitter studies, nerve conduction studies (NCS) to exclude neuropathy, and needle electromyography (EMG) to evaluate for myositis, are also essential for diagnosis 1
• Other tests, such as pulmonary function assessment, complete blood count, comprehensive metabolic panel, thyroid function tests, and inflammatory markers, may be necessary to rule out conditions that can mimic or exacerbate MG 1 It is essential to note that the absence of antibodies does not rule out the syndrome, and clinical correlation with laboratory findings is crucial for accurate diagnosis 1.

From the Research

Laboratory Tests for Diagnosing Myasthenia Gravis (MG)

The diagnosis of Myasthenia Gravis (MG) involves a combination of clinical evaluation and laboratory tests. The following laboratory tests are indicated to diagnose MG:

• Acetylcholine receptor antibodies test: This test is used to detect the presence of antibodies against acetylcholine receptors, which are found in the majority of patients with MG 2.
• Muscle-specific tyrosine kinase (MuSK) antibodies test: This test is used to detect the presence of antibodies against MuSK, which are found in some patients with MG 3, 2.
• Lipoprotein-related protein 4 (LRP4) antibodies test: This test is used to detect the presence of antibodies against LRP4, which are found in some patients with MG 2, 4.
• Edrophonium testing: This test is rarely used but can be helpful in cases of measurable ptosis 5.
• Decremental response on slow-frequency repetitive nerve stimulation: This test has a modest diagnostic yield in ocular MG but is helpful in generalized MG cases 5.
• Single-fiber electromyography: This is the most sensitive test for diagnosing MG 5.

Antibody Testing

Antibody testing is an important part of the diagnostic workup for MG. The following antibodies can be tested:

• Acetylcholine receptor antibodies: These antibodies are found in the majority of patients with MG 2.
• MuSK antibodies: These antibodies are found in some patients with MG 3, 2.
• LRP4 antibodies: These antibodies are found in some patients with MG 2, 4.
• Other antibodies: There are several other antibodies that have been associated with MG, but they are not yet widely available for routine testing 2, 4.

Electrodiagnostic Testing

Electrodiagnostic testing can be used to support the diagnosis of MG. The following tests can be used:

• Repetitive nerve stimulation: This test can be used to detect decremental responses, which are characteristic of MG 5.
• Single-fiber electromyography: This is the most sensitive test for diagnosing MG 5.