Myasthenia Gravis

Lambert-Eaton

  • Auto-antibodies against ACh Receptor
  • POST-synaptic
  • Motor response decreases with successive contractions of voluntary skeletal muscles (particularly ocular, masticatory, facial, deglutition, lingual) WATCH for resp muscle weakness!
  • TENDON reflexes are maintained
  • EMG: a typical decremental response on repetitive stimulation
  • Smooth and cardiac muscle are not involved and other neural functions are typically preserved (NO autonomic dysfunction)
  • Thymectomy is an important treatment option for MG (associated with thymoma and thymic hyperplasia)
  • Atrophy/Pain are typically not reported

 

  • Auto-antibodies against Ca+ channels
  • PRE-synaptic
  • Motor response improves with successive contractions., e.g. improvement of power on repeated hand grip (a phenomenon known as “Lambert’s sign“)
  • At rest, reflexes are typically reduced; with muscle use, reflex strength increases
  • The pupillary light reflex may be sluggish
  • Sometimes causes autonomic (involuntary) symptoms such as dry mouth, constipation, impotence and bladder urgency
  • Lambert-Eaton may be regarded as a paraneoplastic syndrome (60% of LEM have Small cell lung cancer, but only 3% of SCLC experience LEM)

REFERENCES

  1. 461: Myasthenia Gravis and Other Diseases of the Neuromuscular Junction. Daniel B. Drachman; Anthony A. Amato. Harrison’s Principles of Internal Medicine, 19e
  2. Engel  AG, ed. Neuromuscular Junction Disorders. Handbook of Clinical Neurology. Vol 91. Amsterdam: Elsevier; 2008.
  3. Jayawant  S, Parr  J, Vincent  A. Autoimmune myasthenia gravis. Handb Clin Neurol. 2013;113:1465–1468.

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