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AAEM minimonograph #44: Diseases associated with motor unit activity
Author(s) -
Auger Raymond G.
Publication year - 1994
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880171103
Subject(s) - motor unit , fasciculation , neuromyotonia , myokymia , anterior horn cell , electrophysiology , stiff person syndrome , neuroscience , electromyography , agonist , compound muscle action potential , medicine , peripheral , psychology , anatomy , chemistry , receptor , biochemistry , disease , amyotrophic lateral sclerosis , antibody , immunology , glutamate decarboxylase , enzyme
Stiff‐man syndrome is due to hyperexcitability of anterior horn cells, possibly related to interference with the synthesis or action of gammaaminobutyric acid. Unexpected acoustic and exteroceptive stimuli produce exaggerated muscle responses. Needle electrode examination of involved muscles yields nonspecific findings and demonstrates involuntary motor unit activity. The appearance and firing pattern of motor units are normal except that agonist and antagonist muscles may contract concurrently. Continuous muscle fiber activity (Isaacs' syndrome) comprises a heterogeneous group of hereditary and acquired disorders that cause hyperexcitability of peripheral nerves. Some are associated with electrophysiologic evidence of peripheral neuropathy and some are not. Repetitive afterdischarges often follow the M‐, H‐, and F‐waves. Needle electrode examination reveals an abnormal pattern of motor unit firing, consisting of myokymic discharges, doublets and multiplets, neuromyotonic discharges, and fasciculations. These abnormalities may occur alone or in combination.