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Myasthenia Gravis for the American Board of Internal Medicine (ABIM) Exam

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Clinical Features
    • 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.
Treatment Strategies
    • 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.
Prognosis
    • 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.