Abnormal cutaneous silent period in amyotrophic lateral sclerosis

Background/Objectives
The cutaneous silent period (CSP) is an inhibitory reflex that involves suppression of voluntary electromyographic activity following cutaneous nociception. It is mediated by A-delta afferents and alpha-motoneuron efferents. We aimed to investigate changes in upper and lower limb CSP latency and duration in people with amyotrophic lateral sclerosis (ALS).

Methods
We recorded CSP latency and duration in people with ALS and healthy age-matched controls, recording from abductor pollicis brevis and tibialis anterior. The presence of upper motor neuron (UMN) or lower motor neuron (LMN) involvement in studied limbs and Amyotrophic Lateral Sclerosis Functional Rating Scale (ALS-FRS) score was recorded for all individuals.

Results
We assessed fourteen individuals (seven with ALS and seven healthy controls). Median age was 68.3 years, median time from diagnosis 9.7 (range 3.9–15.3) months and median ALS-FRS score 37/48. All individuals with ALS had LMN signs in upper and lower limbs, all had UMN signs in the upper limbs, and six (86%) had UMN signs in the lower limbs. Five (71%) individuals were taking riluzole at time of testing. Lower limb CSP latency was prolonged in those with ALS (median 116.2ms vs. 85.8ms, p<0.05) compared to controls. CSP duration was reduced in ALS compared to controls in both upper limbs (median duration 39.9ms vs. 58.3, p<0.05) and lower limbs (47.1ms vs. 68.8ms, p<0.05).

Conclusion
CSP onset was delayed and CSP duration shortened in ALS compared to controls. Further research is required to elucidate to what extent these changes are driven by corticospinal tract impairment in ALS.