Does myasthenia gravis cause ascending weakness?

Myasthenia Gravis and Pattern of Weakness

Myasthenia gravis does not typically cause ascending weakness; it presents with fatigable muscle weakness that is more proximal than distal, often involving ocular and bulbar muscles first. 1

Clinical Presentation of Myasthenia Gravis

Myasthenia gravis (MG) has a characteristic pattern of weakness that differs from ascending weakness patterns seen in conditions like Guillain-Barré syndrome:

• Typical MG weakness pattern:

  • Fatigable or fluctuating muscle weakness
  • More proximal than distal muscle involvement
  • Frequent ocular involvement (ptosis, extraocular movement abnormalities, diplopia)
  • Bulbar involvement (dysphagia, dysarthria, facial muscle weakness)
  • May include neck and respiratory muscle weakness 1

• Key distinguishing features:

  • Worsens with repeated use of muscles
  • Improves with rest
  • Variable presentation throughout the day
  • Ocular symptoms are the first presentation in 50% of patients 2

Differentiating from Ascending Weakness Patterns

Ascending weakness (starting in lower extremities and progressing upward) is characteristic of Guillain-Barré syndrome (GBS), not myasthenia gravis:

• Guillain-Barré syndrome pattern:
  • Progressive, typically symmetrical muscle weakness
  • Often starts with sensory symptoms/neuropathic pain in lower back and thighs
  • Ascending weakness pattern (though not always)
  • Absent or reduced deep tendon reflexes 1

While rare cases of MG may present with features resembling GBS 3, this is not the typical presentation and should prompt consideration of either concurrent conditions or alternative diagnoses.

Diagnostic Considerations

When evaluating suspected MG, important diagnostic tests include:

• Anti-acetylcholine receptor (AChR) antibodies (positive in 80-85% of patients)
• Anti-muscle specific kinase (MuSK) antibodies (positive in 5-8%)
• Anti-striated muscle antibodies
• Electrodiagnostic studies including:
  • Neuromuscular junction testing with repetitive stimulation
  • Single fiber EMG
• Ice pack test for ocular symptoms
• Edrophonium (Tensilon) test 1, 4

Treatment Approach

Treatment of myasthenia gravis includes:

1. Acetylcholinesterase inhibitors:

   • Pyridostigmine (starting at 30 mg orally three times daily, gradually increasing to maximum of 120 mg four times daily) 1, 5

2. Immunosuppressive therapy:

   • Corticosteroids (prednisone 1-1.5 mg/kg orally daily)
   • Steroid-sparing agents (azathioprine, mycophenolate) 1, 4

3. For severe cases (MGFA class 3-4):

   • IVIG (2 g/kg IV over 5 days)
   • Plasmapheresis 1

4. Thymectomy:

   • Particularly indicated in presence of thymoma
   • May substantially reduce clinical symptoms 1, 2

Important Cautions

• Medication precautions: Avoid medications that can worsen myasthenia including β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 1

• Crisis monitoring: Be vigilant for signs of myasthenic crisis (disease worsening) versus cholinergic crisis (medication overdose), which require opposite management approaches 5

• Respiratory function: Regular assessment of respiratory function is critical as respiratory compromise can occur 1, 2

Myasthenia gravis requires careful diagnosis and individualized treatment to manage symptoms effectively and prevent complications.