Stapedial Reflex: A Possible Novel Biomarker of Early Bulbar Involvement in Amyotrophic Lateral Sclerosis Patients

Background and Aim: Amyotrophic lateral sclerosis (ALS) is a neuromuscular progressive disorder, characterized by limb and bulbar muscle wasting and weakness. 30% of patients present a bulbar onset, while 70% a spinal outbreak, although most of them develop bulbar impairment later on. Due to the lack of an early biomarker of bulbar involvement, we chose to evaluate the role of stapedial reflex (SR) in order to predict preclinical bulbar impairment in ALS. Materials and Methods: We enrolled 36 ALS patients. We assessed revised-ALS functional-rating-scale and SR for a total of 4 visits. We established the presence of SR, acoustic reflex latency test (ARLT), and SRs Decay. Patients who had not develop bulbar signs at fourth visit continued follow-up up to 15 months. Data were analyzed by using Mann-Whitney U test, Friedman test, and Cox regression analysis. Results: We observed that SRs Decay at 500 and 1,000 Hz is the first parameter of SR to get altered in all ALS patients before the development of bulbar impairment. Twenty-eight patients developed bulbar impairment during the study. We highlighted a correlation between the progression rate of disease and both time of SRs Decay alteration and time of bulbar impairment from disease onset. Four patients who did not develop bulbar impairment had a progression rate lower than the other ones (p < 0.05). Discussion and Conclusions: This study shows that SR Decay test could be a sensitive measure for detecting pre-symptomatic bulbar involvement in ALS and could represent a simple, noninvasive, and useful biomarker of disease progression.