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Clinical Presentation
    • Ocular Symptoms: Ptosis and diplopia are often the first symptoms, with variability throughout the day.
    • Generalized Weakness: Affects bulbar, limb, and respiratory muscles; muscle weakness typically worsens with activity and improves with rest.
    • Myasthenic Crisis: Acute exacerbation leading to respiratory failure, often precipitated by infection, surgery, or medication noncompliance.
Diagnosis
    • Serological Tests: Anti-acetylcholine receptor (AChR) antibodies; consider anti-MuSK antibodies if AChR-negative.
    • Electrophysiology: Repetitive nerve stimulation and single-fiber EMG for diagnostic confirmation.
    • Imaging: Chest CT or MRI to evaluate for thymoma.
    • Bedside Tests: Ice pack test can temporarily improve ptosis.
Management
    • Acetylcholinesterase Inhibitors: Pyridostigmine is the first-line treatment to enhance neuromuscular transmission.
    • Immunosuppressive Therapy: Corticosteroids, azathioprine, or mycophenolate mofetil for long-term management.
    • Acute Management:
    • Plasmapheresis or IVIG: Used in myasthenic crisis or preoperatively.
    • Thymectomy: Recommended in patients with thymoma or generalized disease, especially in younger patients.
Complications
    • Myasthenic Crisis: Requires immediate intervention with respiratory support and plasmapheresis or IVIG.
    • Cholinergic Crisis: Caused by excessive acetylcholinesterase inhibitors, leading to increased salivation, diarrhea, and muscle twitching; must differentiate from myasthenic crisis.
Prognosis
    • Generally good with appropriate treatment, but requires ongoing monitoring for disease exacerbation and complications.
Commonly Tested Items on USMLE Step 2 & COMLEX-USA Level 2
    • Diagnosis: Recognizing the clinical presentation and confirming with antibody testing and EMG.
    • Management: Initiation of acetylcholinesterase inhibitors and when to use immunosuppressants or thymectomy.
    • Myasthenic Crisis: Identification, acute management, and differentiation from cholinergic crisis.
    • Thymoma: Association with myasthenia gravis and the role of imaging and surgery.

Related Terms