Myasthenia Gravis for the American Board of Internal Medicine (ABIM) Exam
Clinical Features
Diagnostic Approach
Complications and Monitoring
- Primary Symptoms: Fluctuating skeletal muscle weakness, most commonly presenting with ptosis, diplopia, and bulbar symptoms such as dysphagia and dysarthria.
- Exacerbation Triggers: Infections, surgery, medications (e.g., aminoglycosides, beta-blockers), and emotional stress can exacerbate symptoms.
- Myasthenic Crisis: Life-threatening condition characterized by severe muscle weakness leading to respiratory failure; requires prompt recognition and intervention.
Diagnostic Approach
- Serological Testing: Detection of anti-acetylcholine receptor (AChR) antibodies; anti-MuSK antibodies in AChR-negative patients.
- Electrophysiological Studies: Repetitive nerve stimulation and single-fiber EMG are key diagnostic tools.
- Imaging: Chest CT or MRI to assess for thymoma, which is associated with Myasthenia Gravis in many patients.
- Bedside Testing: Ice pack test can transiently improve ptosis and support diagnosis.
- Symptomatic Management:
- Acetylcholinesterase Inhibitors: Pyridostigmine is the mainstay for symptom relief.
- Immunotherapy:
- Corticosteroids: First-line immunosuppressive treatment.
- Other Immunosuppressants: Azathioprine, mycophenolate mofetil, or cyclosporine for steroid-sparing effects.
- Crisis Management:
- Plasmapheresis or IVIG: Used during myasthenic crisis or preoperatively.
- Surgical Intervention: Thymectomy, particularly indicated in thymoma and often beneficial in generalized disease.
Complications and Monitoring
- Thymoma: Associated with more severe disease and a strong indication for thymectomy.
- Long-term Monitoring: Regular assessment for disease progression, medication side effects, and comorbid conditions.
- With appropriate management, patients can have a good quality of life, but they require ongoing follow-up for potential exacerbations and complications.
Commonly Tested Items on the ABIM Exam
- Diagnosis: Recognizing clinical features and confirming with antibody testing and electrophysiological studies.
- Myasthenic Crisis Management: Immediate interventions, including respiratory support and plasmapheresis or IVIG.
- Thymoma and Thymectomy: Association with Myasthenia Gravis and the role of surgery.
- Medication Management: Understanding when and how to use acetylcholinesterase inhibitors and immunosuppressants, and monitoring for adverse effects.