Cardiothoracic Surgery: Myasthenic Disease

Myasthenia Gravis (MG)

Basics

  • Definition: Acquired Autoimmune Disorder of the Neuromuscular Junction
  • Antibody: Against the Postsynaptic Acetylcholine Receptors (AChR)
    • Reduce Number of Acetylcholine Receptors (AChR) with Use
  • Associations: The Majority Have Thymus Abnormalities
    • Thymus Hyperplasia (60-70%)
    • Thymoma (10-12%)
      • 50% of Patients with Thymoma Have MG

Presentation

  • Proximal Muscle Weakness
    • Fatigue with Use
  • Ocular Symptoms (Diplopia & Ptosis) – Most Common Presenting Symptom
  • Bulbar Muscle (Chewing) Fatigue
  • Facial Muscle Weakness
  • Respiratory Muscle Weakness – Most Serious Consequence

Myasthenic Crisis

  • Definition: Respiratory Failure from Worsening Weakness
  • Precipitating Factors:
    • Infection (Most Common)
    • Surgery/Thymectomy
    • Spontaneous
    • Childbirth
    • Tapering Immunosuppressive Medication

Diagnosis

  • Diagnosis: Antibody Testing

Treatment

  • Symptomatic Treatment: Anticholinesterase Inhibitor (Pyridostigmine/Neostigmine)
  • Acute Therapy/Myasthenic Crisis: Intravenous Immunoglobulin (IVIG) or Plasmapheresis
  • Chronic Therapy: Steroids or Other Immunotherapies (Azathioprine, Cyclosporine, etc.)
  • Thymectomy
    • Indications:
      • Thymoma
      • No Thymoma & Age < 60 Years
    • 80% Symptomatic Improvement (Higher Success Rate in Hyperplasia than Thymoma)
  • Anesthesia Concerns:
    • Unpredictably Resistant to Depolarizing Paralytics (Succinylcholine)
    • Unpredictably Sensitive to Non-Depolarizing Paralytics (Rocuronium, Vecuronium, etc.)

Lambert-Eaton Myasthenic Syndrome (LEMS)

Basics

  • Definition: Acquired Autoimmune Disorder of the Neuromuscular Junction
  • Antibody: Against the Presynaptic Calcium Channels (Prevents Acetylcholine Release)
    • Increased Acetylcholine (ACh) with Use
  • Associations:
    • Small Cell Lung Cancer (SCLC) – About 50%
    • Lymphoproliferative Disorder (Hodgkin Lymphoma)
    • Malignant Thymoma
    • Atypical Carcinoid Tumor

Presentation

  • Proximal Muscle Weakness & Loss of Deep Tendon Reflexes (DTR’s)
    • Improves with Use (Compared to MG)
  • Autonomic Dysfunction (Dry Mouth, Sluggish Pupillary Light Response & Male Impotence)
  • Respiratory Failure – Late in Presentation

Diagnosis

  • Diagnosis: Electrodiagnostic Studies & Antibody Testing
  • Evaluate for Underlying Malignancy

Treatment

  • Mild Symptoms: Nothing
  • Moderate-Severe Weakness: Amifampridine (3,4-Diaminopyridine/3,4-DAP)
    • Refractory Disease:
      • Intravenous Immunoglobulin (IVIG)
      • Steroids
      • Other Immunotherapies (Azathioprine, Cyclosporine, etc.)
  • Treat Underlying Malignancy