Myasthenia Gravis for the Physician Assistant Licensing Exam
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Pathophysiology
Clinical Presentation
Diagnosis
- Autoimmune disorder where antibodies target acetylcholine receptors at the neuromuscular junction.
- Leads to fluctuating muscle weakness, especially in voluntary muscles.
Clinical Presentation
- Muscle Weakness: Progressive weakness that worsens with activity and improves with rest.
- Commonly Affected Areas: Ocular muscles (ptosis, diplopia), bulbar muscles (dysphagia, dysarthria), and generalized weakness.
- Myasthenic Crisis: Acute exacerbation that can cause respiratory failure.
Diagnosis
- Serological Testing: Detection of anti-acetylcholine receptor (AChR) antibodies.
- Electrophysiological Studies: Repetitive nerve stimulation and single-fiber EMG showing a decremental response.
- Clinical Testing: Edrophonium test, though less commonly used.
- Symptomatic:
- Acetylcholinesterase inhibitors (e.g., pyridostigmine) to improve muscle contraction.
- Immunosuppressive Therapy:
- Corticosteroids and other agents (e.g., azathioprine) for long-term control.
- Crisis Management:
- Plasmapheresis or IVIG for rapid symptom relief.
- Surgical Option: Thymectomy, particularly in patients with a thymoma or generalized disease.
- Ongoing Assessment: Monitor respiratory function and muscle strength regularly.
- Complications: Watch for myasthenic crisis and differentiate from cholinergic crisis due to overmedication.
Commonly Tested Items on the Exam
- Recognition of ocular and bulbar symptoms as initial presentations.
- Understanding the use of acetylcholinesterase inhibitors for symptomatic management.
- Differentiation between myasthenic and cholinergic crises.
- The role of thymectomy in treatment, especially with a thymoma.
- Management strategies for myasthenic crisis including the use of plasmapheresis or IVIG.