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Motor cortex excitability in stiff-person syndrome
F Sandbrink1, N A Syed, M D Fujii
1Electromyography Section and Neuromuscular Diseases Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
Brain : a Journal of Neurology
|October 26, 2000
Summary
Stiff-person syndrome (SPS) involves continuous muscle firing due to impaired GABA-ergic neurons. Research suggests motor cortex hyperexcitability, possibly from supraspinal GABA-ergic neuron dysfunction, contributes to SPS symptoms.
Area of Science:
- Neuroscience
- Neurology
- Immunology
Background:
- Stiff-person syndrome (SPS) is characterized by muscle stiffness from continuous motor unit firing.
- This is often attributed to autoimmune dysfunction of GABA-ergic inhibitory neurons.
- However, excessive supraspinal excitation may also contribute to motor neuron hyperactivity.
Purpose of the Study:
- To investigate potential dysfunction in supraspinal GABA-ergic neurons in SPS patients.
- To assess motor cortex excitability using transcranial magnetic stimulation (TMS).
Main Methods:
- Transcranial magnetic stimulation (TMS) was used to evaluate motor cortex excitability in seven SPS patients and seven healthy controls.
- Measurements included motor evoked potentials (MEPs), stimulus-response curves, and paired-pulse TMS paradigms.
- Intracortical inhibition and facilitation were assessed in hand and leg muscles.
Main Results:
- SPS patients showed normal central motor conduction times and MEP thresholds.
- Cortical silent periods in leg muscles were shortened.
- Paired-pulse TMS revealed decreased intracortical inhibition and increased facilitation at short intervals in SPS patients.
Conclusions:
- The findings indicate motor cortex hyperexcitability in SPS.
- This hyperexcitability may stem from impaired supraspinal GABA-ergic neurons.
- An imbalance in intracortical inhibitory and excitatory circuitry likely contributes to SPS pathophysiology.