Split limb phenomenon in amyotrophic lateral sclerosis: electrophysiologic study

Background Amyotrophic lateral sclerosis (ALS) is a degenerative disease that affects the upper and lower motor neurons.

The onset of the disease is frequently focal, usually involving the distal segments of the extremities.

A dissociated pattern of muscle atrophy is commonly found in the hands and feet.

This study aims to investigate the presence (if any) of split indices in ALS patients and to correlate these indices with confounding factors.

A total of 48 people were studied.

The control group consists of 24 ALS patients and another 24 age- and gender-matched patients.

To assess functional status and muscle strength, the ALS functional rating scale (ALSFRS) and the Medical Research Council (MRC) were used, respectively.

Sensory and motor nerve conduction, as well as compound muscle action potential (CMAP) amplitude, were recorded from the muscles of the upper and lower limbs.

The electromyographic (EMG) activity of 20 motor unit action potentials (MUAPs) from four different areas was also studied.

Results Distal CMAP amplitude was reduced in all tested muscles (especially noticed when comparing the reciprocal muscles).

In ALS patients, the split foot index (SFI) is significantly higher, while the split elbow index (SEI) is significantly lower.

The split foot index (SFI) was found to be negatively related to disease duration, but positively related to ALSFRS scores.

The CMAP amplitude was found to be positively related to the MRC score.

Conclusion Ankle dorsiflexion muscles are more involved (dissociated) than plantar flexor muscles, and elbow flexors are more involved than extensors.

SFI correlates significantly with disease duration and ALSFRS scores.