Segmental motoneuronal dysfunction is a feature of amyotrophic lateral sclerosis

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Journal Article
Clinical Neurophysiology, 2015, 126 (4), pp. 828 - 836
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© 2014 International Federation of Clinical Neurophysiology. Objectives: There is accumulating evidence of dysfunction of spinal circuits in the pathogenesis of amyotrophic lateral sclerosis (ALS). Methods: The present study was undertaken to characterise the pathophysiological changes in segmental motoneuronal excitability in 28 ALS patients, using recruitment curves of the soleus H-reflex and M-wave, compared with clinical assessments of upper motor neuron (UMN) and lower motor neuron dysfunction. Results: H-reflex recruitment curves established that Hmax/Mmaxand slope (Hθ/Mθ) ratios predicted clinical UMN dysfunction (p<0.001). Changes in Hθ/Mθwere driven by reduced Mθ. Assessment of Hmax/Mmaxwas similar in the ALS and control groups, and was affected by overlap of the H and M recruitment curves in ALS patients. Conclusion: Changes in the slope ratio (Hθ/Mθ) in ALS suggested that alterations in peripheral motor nerve excitability following UMN damage may affect the recorded H-reflex. Increased collision of reflex discharges with antidromically-conducted motor impulses may be exacerbated in ALS due to preferential loss of large-caliber α-motoneurones, which may explain the similarities in Hmax/Mmaxbetween groups. Significance: Findings from the present study provide further insight into the pathophysiology of ALS, specifically the relative contributions of premotoneuronal and segmental motoneuronal dysfunction.
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