# Contralateral R1 response in blink reflex in patients with amyotrophic lateral sclerosis

## TL;DR

This study shows that a specific blink reflex response is more common in ALS patients and could help in diagnosis.

## Contribution

The study identifies a potential biomarker for ALS based on the frequency of contralateral R1 responses in the blink reflex.

## Key findings

- Contralateral R1 responses (R1′) were more frequent in ALS patients compared to non-ALS and healthy volunteers.
- Bilateral R1′ was observed only in ALS patients and absent in other groups.
- R1′ frequency was higher in ALS patients with pseudobulbar affect compared to those without.

## Abstract

•Contralateral R1 responses (R1′) in the blink reflex are more frequent in ALS patients than non-ALS and healthy volunteers.•Bilateral R1′ was specific to ALS, observed in a quarter of the ALS group and absent in non-ALS and healthy volunteers.•R1′ in ALS may serve as a diagnostic biomarker though it lacks sensitivity and must be interpreted in the clinical context.

Contralateral R1 responses (R1′) in the blink reflex are more frequent in ALS patients than non-ALS and healthy volunteers.

Bilateral R1′ was specific to ALS, observed in a quarter of the ALS group and absent in non-ALS and healthy volunteers.

R1′ in ALS may serve as a diagnostic biomarker though it lacks sensitivity and must be interpreted in the clinical context.

This study aimed to compare the frequency of blink reflex’s contralateral R1 responses (R1′) between patients with amyotrophic lateral sclerosis (ALS), non-ALS motor deficit patients, and healthy volunteers.

A total of 120 participants were prospectively recruited: 40 with ALS, 40 with a non-ALS motor deficit, and 40 healthy volunteers. Blink reflexes were recorded from orbicularis oculi muscles following supraorbital nerve stimulation.

R1′ was more frequent in the ALS group (42.5 %) compared to healthy volunteers (12.5 %, p = 0.00588), and compared to non-ALS patients (7.5 %, p = 0.000789). Bilateral R1′ was observed only in ALS patients (22.5 %). No clinically significant difference was found in the latencies or amplitudes of the R1, R2, or R1′ responses among groups. R1′ was more frequent in ALS patients with pseudobulbar affect (71.4 %) compared to those without (36.4 %).

The higher frequency of R1′ in ALS highlights its potential role in distinguishing ALS from other motor disorders. Its sensitivity was low, but bilateral R1′ was specific to ALS. The higher frequency of R1′ among ALS patients with pseudobulbar affect potentially reflects corticobulbar neuron degeneration.

The R1′, especially when bilateral, could serve as an additional diagnostic biomarker for ALS, although its clinical relevance should be considered within the broader diagnostic context.