Myasthenia Gravis for USMLE Step 3 & COMLEX-USA Level 3
Clinical Presentation and Diagnosis
Management and Treatment
Complications
- Initial Symptoms: Fluctuating muscle weakness, especially in ocular muscles (ptosis, diplopia), with progression to generalized weakness.
- Differential Diagnosis: Differentiate from other causes of muscle weakness, such as Lambert-Eaton myasthenic syndrome, botulism, and stroke.
- Key Diagnostic Tests:
- Serology: Anti-acetylcholine receptor (AChR) antibodies; anti-MuSK antibodies for AChR-negative patients.
- Electrophysiology: Repetitive nerve stimulation and single-fiber EMG.
- Imaging: Chest CT or MRI to rule out thymoma.
- Bedside Tests: Ice pack test can help confirm diagnosis in ptosis.
Management and Treatment
- First-line Treatment:
- Acetylcholinesterase Inhibitors: Pyridostigmine for symptom management.
- Long-term Management:
- Immunosuppressants: Corticosteroids, azathioprine, mycophenolate mofetil, or cyclosporine.
- Thymectomy: Recommended for thymoma and often in generalized disease.
- Crisis Management:
- Myasthenic Crisis: Requires intensive care, mechanical ventilation, and plasmapheresis or IVIG.
- Cholinergic Crisis: Differentiate from myasthenic crisis; management includes discontinuing acetylcholinesterase inhibitors and supportive care.
Complications
- Respiratory Failure: Particularly during myasthenic crisis, necessitating prompt recognition and treatment.
- Thymoma: Associated with more severe disease; thymectomy can be curative in some cases.
- Requires long-term management and monitoring for disease progression and treatment-related side effects.
Commonly Tested Items on Step 3
- Crisis Management: Differentiating and managing myasthenic vs. cholinergic crisis.
- Thymectomy: Indications and outcomes, especially in relation to thymoma.
- Immunosuppressive Therapy: Long-term management and monitoring for side effects.
- Complex Cases: Considerations in pregnancy, surgery, and infections that might exacerbate symptoms.