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Corticomotoneuronal connections in primary lateral sclerosis (PLS)
Markus Weber1, Heather Stewart, Nobuyuki Hirota
1Neuromuscular Diseases Unit, Vancouver Hospital, University of British Columbia, Canada. markus.weber@kssg.ch
Summary
Primary lateral sclerosis (PLS) shows higher cortical excitability thresholds and longer motor evoked potential (MEP) peak durations compared to amyotrophic lateral sclerosis (ALS), indicating distinct corticomotoneuronal dysfunction.
Area of Science:
- Neuroscience
- Neurology
- Motor Neuron Diseases
Background:
- The exact relationship between primary lateral sclerosis (PLS) and amyotrophic lateral sclerosis (ALS) remains unclear.
- PLS is characterized by slow progression and upper motor neuron symptoms, often with high cortical stimulation thresholds.
- Amyotrophic lateral sclerosis (ALS) may present with reduced cortical thresholds and normal central motor conduction early in the disease.
Purpose of the Study:
- To investigate and compare corticomotoneuronal function in patients with PLS and ALS.
- To differentiate the neurophysiological underpinnings of PLS and ALS through advanced analysis.
Main Methods:
- Assessed corticomotoneuronal function using peristimulus time histograms (PSTHs) in 12 PLS and 12 ALS patients.
- Measured surface-recorded motor evoked potentials (MEPs) and central motor conduction time (CMCT).
- Analyzed PSTH primary peak parameters: onset latency, duration, and synchrony from voluntarily recruited motor units.
Main Results:
- The mean cortical threshold for single motor units was significantly higher in PLS (73.6%) than in ALS (60.3%).
- Delayed primary peaks in PSTHs were observed in both PLS and ALS.
- The duration of the primary peak in PSTHs was significantly longer in PLS compared to ALS.
Conclusions:
- Distinct patterns in primary peak duration and cortical threshold suggest different excitability and corticomotoneuronal pathway involvement in PLS versus ALS.
- The findings indicate a greater loss of corticomotoneuronal connections in PLS compared to ALS, contributing to disease-specific neurophysiological profiles.