From the Guidelines
The diagnosis of myasthenia gravis (MG) should begin with a thorough history and physical examination, followed by serological testing for acetylcholine receptor (AChR) antibodies, and if negative, testing for muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4) antibodies, as recommended by the most recent guidelines 1. The workup and diagnosis of MG involve a combination of clinical evaluation, serological testing, electrophysiological studies, and imaging.
- Initial evaluation should include:
- AChR and antistriated muscle antibodies in blood
- Pulmonary function assessment with NIF and VC
- CPK, aldolase, ESR, and CRP for possible concurrent myositis
- Consider MRI brain and/or spine depending on symptoms to rule out CNS involvement by disease or alternate diagnosis
- Electrophysiological studies, under neurologic consultation, including neuromuscular junction testing with repetitive stimulation and/or jitter studies, NCS to exclude neuropathy, and needle EMG to evaluate for concomitant myositis, are essential for diagnosis 1.
- Inflammatory markers (ESR and CRP) and consideration of paraneoplastic workup should also be included in the diagnostic process.
- It is crucial to review and stop medications with known risk of worsening myasthenia, such as beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 1. The diagnosis is confirmed when clinical features are supported by positive antibody tests and/or characteristic electrophysiological findings.
- Early diagnosis is crucial as prompt treatment with acetylcholinesterase inhibitors, immunosuppressants, and in some cases thymectomy can significantly improve outcomes and prevent life-threatening complications like myasthenic crisis, as noted in recent studies 1. The management of MG requires a multidisciplinary approach, including the training and clinical judgment of an experienced ophthalmologist typically working in concert with a treating neurologist 1.
From the FDA Drug Label
ENLON Test in the Differential Diagnosis of Myasthenia Gravis ... Responses to ENLON in myasthenic and nonmyasthenic individuals are summarized in the following chart
- Myasthenic Response- occurs in untreated myasthenics and may serve to establish diagnosis; in patients under treatment, indicates that therapy is inadequate.
The workup and diagnosis of myasthenia gravis can involve the use of edrophonium (ENLON) as a diagnostic tool.
- Myasthenic Response: occurs in untreated myasthenics and may serve to establish diagnosis; in patients under treatment, indicates that therapy is inadequate.
- The ENLON test can help differentiate between myasthenic and cholinergic crises.
- The test involves administering a small dose of ENLON intravenously and observing the patient's response.
- A myasthenic response is characterized by increased muscle strength, while a cholinergic response is characterized by severe side reactions and decreased muscle strength 2.
- Edrophonium (ENLON) is recommended for the differential diagnosis of myasthenia gravis and as an adjunct in the evaluation of treatment requirements in this disease 2.
From the Research
Diagnostic Approach
The diagnosis of myasthenia gravis (MG) is primarily clinically based, with diagnostic tests used to reaffirm the clinician's impression 3. The diagnostic approach involves a combination of clinical evaluation, laboratory tests, and electrodiagnostic tests.
Clinical Evaluation
The clinical evaluation involves assessing the patient's symptoms and signs, which can include ptosis, diplopia, facial bulbar weakness, and limb weakness 4. The patient's history and neurologic examination are essential in making a diagnosis of MG.
Laboratory Tests
Laboratory tests, such as acetylcholine receptor (AChR) antibody testing, can help confirm the diagnosis of MG 4, 5. AChR antibodies are found in 80%-85% of patients with MG. Other antibodies, such as muscle-specific kinase (MuSK) and low-density lipoprotein receptor-related protein 4 (Lrp4), can also be present in some patients with MG.
Electrodiagnostic Tests
Electrodiagnostic tests, such as repetitive nerve stimulation and single-fiber electromyography (EMG), can help diagnose MG 3, 4, 5. Single-fiber EMG is the most sensitive test for diagnosing MG. The edrophonium test can also be used to diagnose MG, particularly in cases of measurable ptosis 3, 6.
Diagnostic Tests
The following diagnostic tests can be used to diagnose MG:
- Repetitive nerve stimulation
- Single-fiber EMG
- Edrophonium test
- AChR antibody testing
- MuSK antibody testing
- Lrp4 antibody testing
Classification of MG
MG can be classified based on the presence of serum autoantibodies and clinical presentation 4, 7. The classification of MG can help guide treatment and predict treatment response.