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AAEM minimonograph #44: diseases associated with excess motor unit activity
1Department of Neurology, Mayo Clinic, Rochester, Minnesota.
Muscle & Nerve
|November 1, 1994
Summary
Stiff-man syndrome and Isaacs' syndrome involve nerve hyperexcitability, affecting muscle responses. Electromyography shows abnormal motor unit activity, indicating neurological dysfunction.
Area of Science:
- Neurology
- Neurophysiology
Background:
- Stiff-man syndrome (SMS) is linked to anterior horn cell hyperexcitability, potentially involving gamma-aminobutyric acid (GABA) pathways.
- Continuous muscle fiber activity, or Isaacs' syndrome, is a group of disorders causing peripheral nerve hyperexcitability.
Purpose of the Study:
- To describe the neurophysiological underpinnings of Stiff-man syndrome and Isaacs' syndrome.
- To detail the findings of needle electrode examination in these conditions.
Main Methods:
- Review of clinical and electrophysiological data for patients with Stiff-man syndrome and Isaacs' syndrome.
- Analysis of needle electrode examination findings, focusing on motor unit activity patterns.
Main Results:
- Stiff-man syndrome exhibits exaggerated muscle responses to stimuli and involuntary motor unit activity, with concurrent agonist and antagonist muscle contractions.
- Needle electrode examination in Isaacs' syndrome reveals myokymic discharges, doublets, multiplets, neuromyotonic discharges, and fasciculations, with or without peripheral neuropathy.
Conclusions:
- Both Stiff-man syndrome and Isaacs' syndrome are characterized by neuronal hyperexcitability.
- Electromyography is crucial for diagnosing these disorders by identifying specific patterns of abnormal motor unit firing.