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Magnetic stimulation in Alzheimer's disease
M de Carvalho1, A de Mendonça, P C Miranda
1Department of Neurology, Hospital de Santa Maria, Lisbon, Portugal.
Abstract:
Alzheimer's disease (AD) is a common cause of dementia in which some clinical motor abnormalities have been described. We used transcranial magnetic stimulation in order to test the hypothesis that the change in the motor cortex might cause modifications in motor excitability. Fourteen mildly to moderately affected AD patients were compared with 11 controls matched for age, height and sex. The motor evoked potential threshold value for the relaxed abductor digiti minimi was lower in the AD patients than in the control group for both left and right hemispheres (P < 0.05). No statistically significant difference was found comparing the left and the right hemispheres thresholds in each population. The mean interside threshold differences were small and not significantly different between patients and controls. The spinal motor neuron excitability, as evaluated by F/M and H/M waves amplitude ratios, showed no difference between the groups, reinforcing the motor cortex increased excitability hypothesis to explain this difference. Degeneration of inhibitory gabaergic terminals might be the basis for the increased cortical excitability in the motor cortex of the Alzheimer patients; postsynaptic changes in the GABAA receptors might also affect inhibitory gabaergic transmission. The increased excitability found by transcranial magnetic stimulation in the motor cortex is important for understanding the emergence of seizures and myoclonus in this disease.
Insights
Alzheimer's disease (AD) patients exhibit increased motor cortex excitability, as shown by transcranial magnetic stimulation. This heightened cortical excitability may contribute to motor abnormalities and seizures in AD.
Area of Science:
- Neuroscience
- Neurology
- Clinical Medicine
Background:
- Alzheimer's disease (AD) is a leading cause of dementia, often presenting with motor abnormalities.
- The underlying neurophysiological mechanisms of these motor symptoms in AD are not fully understood.
Purpose of the Study:
- To investigate motor cortex excitability in Alzheimer's disease patients using transcranial magnetic stimulation (TMS).
- To test the hypothesis that altered motor cortex excitability contributes to motor abnormalities in AD.
Main Methods:
- Transcranial magnetic stimulation (TMS) was employed to assess motor evoked potential (MEP) thresholds.
- Fourteen patients with mild to moderate Alzheimer's disease were compared with 11 age, height, and sex-matched healthy controls.
- Spinal motor neuron excitability was evaluated using F/M and H/M wave amplitude ratios.
Main Results:
- AD patients demonstrated significantly lower motor evoked potential thresholds in both left and right motor cortices compared to controls (P < 0.05).
- No significant differences in interhemispheric threshold differences were observed between groups.
- Spinal motor neuron excitability remained unchanged, supporting increased cortical excitability as the primary finding.
Conclusions:
- Alzheimer's disease is associated with increased excitability in the motor cortex.
- This heightened excitability may stem from degeneration of inhibitory GABAergic terminals or postsynaptic changes in GABAA receptors.
- Understanding this increased motor cortex excitability is crucial for explaining seizures and myoclonus in Alzheimer's disease.