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