Terminal latency abnormality in amyotrophic lateral sclerosis without split hand syndrome

Area of Science:

• Neurology
• Neurophysiology

Background:

• Amyotrophic lateral sclerosis (ALS) presents unique clinical and electrophysiological patterns, including the 'split hand syndrome' and abnormal abductor pollicis brevis (APB)/abductor digiti minimi (ADM) ratios.
• Cervical spondylotic amyotrophy (CSA) shares some clinical features with ALS, necessitating precise diagnostic tools.

Purpose of the Study:

• To identify significant electrophysiological parameters differentiating upper limb onset ALS from cervical spondylotic amyotrophy (CSA) and healthy controls, particularly in patients with normal APB/ADM ratios.
• To investigate the role of distal axonopathy in ALS pathogenesis.

Main Methods:

• Retrospective analysis of electrophysiological data from 47 upper limb onset ALS patients, 42 CSA cases, and 20 healthy controls.
• Comparison of electrophysiological parameters, including nerve amplitudes, latencies, and ratios, focusing on individuals with normal APB/ADM ratios (0.6–1.7).

Main Results:

• Statistically significant differences (p < 0.05) were observed in median and ulnar nerve amplitudes, median nerve terminal latency, median and ulnar F-wave latencies, ulnar/median nerve terminal latency ratio, and ulnar/median nerve F-wave latency ratio between ALS, CSA, and control groups.
• The median nerve terminal latency and ulnar/median nerve terminal latency ratio were significantly different in ALS patients compared to both CSA and control groups (p < 0.006).

Conclusions:

• Abnormalities in median nerve terminal latency and ulnar/median nerve terminal latency ratio are key electrophysiological indicators in upper limb onset ALS, even when the APB/ADM ratio is normal.
• These findings support the hypothesis that distal motor axonal dysfunction, potentially due to ion channel abnormalities, plays a crucial role in ALS pathogenesis.