Stapedial reflex in amyotrophic lateral sclerosis

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.

Effects of thiocolchicoside, a commonly used myorelaxant, on the acoustic reflex

OBJECTIVE

To determine whether thiocolchicoside, a commonly used myorelaxant, may impair the acoustic reflex.

METHODS

Forty-two patients scheduled to receive thiocolchicoside treatment for different reasons were enrolled in the study. Acoustic reflex thresholds at 500, 1000, 2000 and 4000 Hz were determined and analysed statistically pre-treatment and on the 5th day of treatment.

RESULTS

Increases were observed in the mean acoustic reflex thresholds on the 5th day of treatment compared to pre-treatment, at all frequencies, except right contralateral thresholds at 500 and 2000 Hz. These increases were statistically significant for right ipsilateral thresholds at 2000 and 4000 Hz, left ipsilateral thresholds at 500, 1000, 2000 and 4000 Hz, and left contralateral thresholds at 2000 and 4000 Hz (p ≤ 0.05), but not at other frequencies (p > 0.05).

CONCLUSION

Muscle relaxant drugs, especially those affecting the central nervous system, may weaken the stapedial muscle so that the ability of noise to cause acoustic trauma may become evident. For this reason, physicians should advise their patients to avoid loud noises when muscle relaxant therapy is prescribed.

Assessment of the Brainstem-Mediated Stapedius Muscle Reflex in Andean Children Living at High Altitudes

Counter, S. Allen, Leo H. Buchanan, Fernando Ortega, Anthony B. Jacobs, and Göran Laurell. Assessment of the brainstem-mediated stapedius muscle reflex in Andean children living at high altitudes. High Alt Med Biol. 18:37-45, 2017.-This study examined the physiological thresholds, amplitude growth, and contraction duration of the acoustic stapedius reflex (ASR) in Andean children aged 2-17 years living at altitudes of 2850 m (Altitude I Group) and 3973 m (Altitude II Group) as part of a general medical assessment of the health status of the children. The brainstem-mediated ASR reveals the integrity of the neuronal components of the auditory reflex arc, including the cochlea receptors, eight cranial nerves, and brainstem neural projections to the cochlear nuclei, bilateral superior olivary nuclei, facial nerve nuclei, and facial nerve and its stapedius branch. Uncrossed (ipsilateral) and crossed (contralateral) ASR thresholds (ASRT), ASR amplitude growth (ASRG) function, and ASR muscle contraction duration (decay/fatigue) (ASRD) were measured noninvasively with 500, 1000 Hz and broadband (bandwidth = 125-4000 Hz) noise stimulus activators using a middle ear immittance system. Oxygen saturation (SaO₂) level and heart rate were measured in a subsample of the study group. Statistical analyses revealed that the Altitude I and Altitude II groups had ASRT, ASRG function, and ASRD rates comparable to children at sea level and that the two groups were not significantly different for any of the ASR measures. No significant association was found between SaO₂ or heart rate and ASRT, growth, and muscle fatigue rate. In conclusion, the assessment of the ASR in children in the high-altitude groups revealed normal function. Furthermore, the results indicate no adverse oto-physiological effects of altitude on the brainstem-mediated ASR at elevations between 2850 and 4000 m and suggest normal middle ear and auditory brainstem function.

Auditory brainstem circuits that mediate the middle ear muscle reflex

The middle ear muscle (MEM) reflex is one of two major descending systems to the auditory periphery. There are two middle ear muscles (MEMs): the stapedius and the tensor tympani. In man, the stapedius contracts in response to intense low frequency acoustic stimuli, exerting forces perpendicular to the stapes superstructure, increasing middle ear impedance and attenuating the intensity of sound energy reaching the inner ear (cochlea). The tensor tympani is believed to contract in response to self-generated noise (chewing, swallowing) and non-auditory stimuli. The MEM reflex pathways begin with sound presented to the ear. Transduction of sound occurs in the cochlea, resulting in an action potential that is transmitted along the auditory nerve to the cochlear nucleus in the brainstem (the first relay station for all ascending sound information originating in the ear). Unknown interneurons in the ventral cochlear nucleus project either directly or indirectly to MEM motoneurons located elsewhere in the brainstem. Motoneurons provide efferent innervation to the MEMs. Although the ascending and descending limbs of these reflex pathways have been well characterized, the identity of the reflex interneurons is not known, as are the source of modulatory inputs to these pathways. The aim of this article is to (a) provide an overview of MEM reflex anatomy and physiology, (b) present new data on MEM reflex anatomy and physiology from our laboratory and others, and (c) describe the clinical implications of our research.

Brainstem mediation of the stapedius muscle reflex in hydranencephaly

Hydranencephaly is a rare condition in which the cerebral hemispheres are absent at birth and are replaced by membranous sacs in a cerebrospinal fluid-filled cranium. Surviving hydranencephalic patients have a functional brainstem and possible remnants of the cerebral cortex. This case report examines hearing function and the integrity of the brainstem mediated stapedius muscle reflex (SMR) in an adult with hydranencephaly, using middle ear impedance change measures. The brainstem mediated ipsilateral and cross-brainstem contralateral SMRs were elicited in the right ear at normal threshold levels for noise bands of 0.25-1.0, 1.0-4.0, and 0.25-4.0 kHz (broadband), and at the sinusoidal frequencies of 0.5, 1.0, and 2.0 kHz. The ipsilateral and contralateral SMR decay rates were normal. The growth in the SMR amplitude in response to noise and pure tone stimuli from threshold to saturation over a 15-20 dB range was normal and showed essentially sigmoidal curves. The normal ipsilateral and crossed brainstem contralateral electrophysiological SMR in this hydranencephalic patient demonstrated the preservation of peripheral hearing reception and functional brainstem auditory afferent and efferent tracts and nuclei in the absence of corticofugal influence.

Electrodiagnostic studies in amyotrophic lateral sclerosis and other motor neuron disorders

The clinical electrodiagnostic medicine (EDX) consultant asked to assess patients with suspected amyotrophic lateral sclerosis (ALS) has a number of responsibilities. Among the most important is to provide a clinical assessment in conjunction with the EDX study. The seriousness of the diagnoses and their enormous personal and economic impact require a high-quality EDX study based on a thorough knowledge of and experience with motor neuron diseases (MNDs) and related disorders. Clinical evaluation will help determine which of the EDX tools available to the EDX consultant should be applied in individual patients. Although electromyography (EMG) and nerve conduction study are the most valuable, each of the following may be helpful in the assessment of selected patients based on their clinical findings: repetitive nerve stimulation, motor unit number estimate, single-fiber EMG, somatosensory evoked potential, autonomic function test, and polysomnography. The pertinent literature on these is reviewed in this monograph. The selection and application of these EDX tools depend on a thorough knowledge of the MNDs and related disorders.