What are the diagnostic criteria and laboratory tests for myasthenia gravis (Myasthenia Gravis, MG) evaluation?

From the Guidelines

The diagnosis of myasthenia gravis should include AChR and antistriated muscle antibodies in blood, and if negative, consider MuSK and LRP4 antibodies, along with electrodiagnostic studies and pulmonary function assessment. The evaluation of myasthenia gravis involves a combination of clinical assessment and laboratory tests, including blood work to identify specific antibodies 1.

Key Laboratory Tests

• AChR and antistriated muscle antibodies in blood 1
• MuSK and LRP4 antibodies if AChR antibodies are negative 1
• CPK, aldolase, ESR, and CRP for possible concurrent myositis 1
• Inflammatory markers (ESR and CRP) 1

Additional Evaluations

• Pulmonary function assessment with NIF and VC 1
• Electrodiagnostic studies, including neuromuscular junction testing with repetitive stimulation and/or jitter studies, NCS to exclude neuropathy, and needle EMG to evaluate for concomitant myositis 1
• Consider MRI brain and/or spine depending on symptoms to rule out CNS involvement by disease or alternate diagnosis 1
• Troponin, ECG, and consider TTE and/or cardiac MRI to evaluate concomitant myocarditis 1

Management Considerations

• Review and stop medications with known risk of worsening myasthenia: beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 1
• Consider paraneoplastic workup 1

From the Research

Myasthenia Gravis Evaluation

Myasthenia gravis (MG) is an autoimmune disease characterized by dysfunction of the neuromuscular junction resulting in skeletal muscle weakness 2. The evaluation of MG includes:

• Clinical presentation: Ptosis, diplopia, facial bulbar weakness, and limb weakness are the most common symptoms 2
• Serologic testing:
  • Acetylcholine receptor (AChR) antibodies are found in 80%-85% of patients 2
  • Muscle-specific kinase (MuSK) antibodies in 5%-8% of patients 2
  • Low-density lipoprotein receptor-related protein 4 (Lrp4) antibodies in <1% of patients 2
• Additional tests:
  • Repetitive nerve stimulation 2
  • Single fiber EMG 2
  • The ice pack test 2

Lab Testing for Diagnosis

Lab testing for MG diagnosis includes:

• Serum autoantibody tests: to detect AChR, MuSK, and Lrp4 antibodies 2, 3, 4, 5
• Edrophonium testing: to assess the response to acetylcholinesterase inhibitors 6, 5
• Electrophysiological tests: such as repetitive nerve stimulation and single fiber EMG 2

Classification of Myasthenia Gravis

MG can be classified based on the presence of serum autoantibodies:

• AChR-MG: characterized by the presence of AChR antibodies 2, 5
• MuSK-MG: characterized by the presence of MuSK antibodies 2, 4, 5
• Double seronegative MG: characterized by the absence of AChR and MuSK antibodies 5