Difference in distribution of fasciculations between multifocal motor neuropathy and amyotrophic lateral sclerosis

To examine differences in fasciculation distribution between patients with multifocal motor neuropathy (MMN) and amyotrophic lateral sclerosis (ALS) based on muscle ultrasound.

Forty-one muscles (tongue muscle and 40 muscles of the trunk and limbs on both sides) in 5 MMN patients and 21 muscles (tongue muscle and 20 muscles on the onset side) in 21 ALS patients were subjected to muscle ultrasound individually for 60 seconds to detect the presence of fasciculations.

Fasciculation detection rates on the onset side were significantly higher in ALS (42.4 ± 18.3%, mean ± SD) than in MMN (21.9 ± 8.8%) patients (p < 0.05). In MMN patients, no fasciculation was detected in the tongue or truncal muscles. There was no difference in the fasciculation detection rate between the onset and non-onset sides or between upper and lower limbs in MMN patients.

In MMN patients, fasciculations were detected extensively in the limbs. However, the detection rate in patients with MMN was lower than in those with ALS.

Demonstration of the absence of fasciculations in the tongue and truncal muscles in MMN patients by extensive muscle ultrasound examination may help distinguish MMN from ALS.