Evoked Potentials

Evoked potentials provide a noninvasive, sensitive, and quantitative way to assess the functional integrity of the somatosensory, auditory, and visual pathways. The basic principle of evoked potentials is to apply a stimulus (sensory, auditory, or visual) in a controlled manner to create a volley of depolarization and repolarization. This stimulus volley ascends through the peripheral and central sensory, auditory, or visual pathways and can be recorded as the signals pass underneath recording electrodes. The generated evoked potential waveforms can represent either a traveling wave of depolarization in white matter or a stationary depolarization within gray matter. The use of somatosensory and brainstem auditory evoked potentials for outpatients has decreased in the past decades as the quality and availability of neuroimaging have improved; however, their use has had a resurgence in electrophysiologic monitoring and mapping of surgical cases involving the spine, posterior fossa, and supratentorial lesions, for which they are now a part of the standard of care.

Increased Gain in the Auditory Pathway, Alzheimer’s Disease Continuum, and Air Pollution: Peripheral and Central Auditory System Dysfunction Evolves Across Pediatric and Adult Urbanites

A major impediment in early diagnosis of Alzheimer’s disease (AD) is the lack of robust non-invasive biomarkers of early brain dysfunction. Metropolitan Mexico City (MMC) children and young adults show hyperphosphorylated tau, amyloid-β, and α-synuclein within auditory and vestibular nuclei and marked dysmorphology in the ventral cochlear nucleus and superior olivary complex. Based on early involvement of auditory brainstem centers, we believe brainstem auditory evoked potentials can provide early AD biomarkers in MMC young residents. We measured brainstem auditory evoked potentials in MMC clinically healthy children (8.52 ± 3.3 years) and adults (21.08 ± 3.0 years, 42.48 ± 8.5 years, and 71.2 ± 6.4 years) compared to clean air controls (6.5 ± 0.7 years) and used multivariate analysis adjusting for age, gender, and residency. MMC children had decreased latency to wave I, delays in waves III and V, and longer latencies for interwave intervals, consistent with delayed central conduction time of brainstem neural transmission. In sharp contrast, young adults have significantly shortened interwave intervals I–III and I–V. By the 5th decade, wave V and interval I–V were significantly shorter, while the elderly cohort had significant delay in mean latencies and interwave intervals. Compensatory plasticity, increased auditory gain, cochlear synaptopathy, neuroinflammation, and AD continuum likely play a role in the evolving distinct auditory pathology in megacity urbanites. Understanding auditory central and peripheral dysfunction in the AD continuum evolving and progressing in pediatric and young adult populations may shed light on the complex mechanisms of AD development and help identify strong noninvasive biomarkers. AD evolving from childhood in air pollution environments ought to be preventable.

The Relationship between Occupationally Exposed Arsenic, Cadmium and Lead and Brain Bioelectrical Activity—A Visual and Brainstem Auditory Evoked Potentials Study

The aim of this study was to evaluate the parameters of visual and brainstem auditory evoked potentials in patients occupationally exposed to arsenic, cadmium and lead. The study group comprised 41 copper smelter and refinery workers (average age: 51.27) with occupational exposure to arsenic, cadmium and lead. The control group consisted of 36 healthy volunteers (35 men and 1 woman, aged 27–66, average age: 51.08). Neurological examination, brain imaging, and visual and brainstem auditory evoked potentials were performed, and the relationship between blood Cd, Pb concentration (Cd-B, Pb-B), blood zinc protoporphyrin (ZnPP), and urine As concentration (As-U) were assessed. In the workers, exceedances of allowable biological concentrations were observed, with the urinary concentration of arsenic being 5.2%, the cadmium and lead in blood being 1.3%, while the case of ZnPP was 2.6%. The mean P100, relative P100, and N145 visual evoked potential (VEP) latencies were significantly longer in exposed workers than in the controls. The mean wave III and V brainstem auditory evoked potential (BAEP) latency and the mean wave III–V and I–V interpeak latencies were longer, and the I and V amplitude was lower in the workers than the controls. In summary, occupational exposure to As, Cd, and Pb is associated with prolonged latency and reduced evoked potential amplitude, but As-U, Pb-B, Cd-B, and ZnPP concentrations are not linearly related to potential components. The analysis of evoked potentials may be a useful method of assessment of the central nervous system in patients with occupational exposure to heavy metals.

Assessment of Visual and Brainstem Auditory Evoked Potentials in Patients with Hashimoto’s Thyroiditis

Background. The present study was aimed to evaluate parameters of visual and brainstem auditory evoked potentials (VEP, BAEP) in euthyreotic Hashimoto’s thyroiditis (HT) patients without central nervous system involvement. Methods. 100 HT patients (92 women, 8 men), mean age 46.9 years, and 50 healthy controls. They underwent a neurological examination, thyroid hormone levels, thyroid autoantibody titers, and brain imaging. Latencies and amplitudes of the N75, P100, and N145 component of VEP and the I-V components of BAEP were analyzed. Results. The neurological examination revealed in 31 patients signs of increased neurovegetative excitability. Brain resonance imaging showed no abnormalities in HT patients. The mean P100, relative P100, and N145 VEP latencies were significantly longer, and P100 amplitude significantly higher in HT patients than the controls. HT patients also had a longer mean wave BAEP V latency and mean wave III-V and I-V interpeak latencies, and significantly lower mean wave I and V amplitudes. Abnormal VEP and BAEP were recorded in 34% of the patients. There were no statistically significant correlations between the mean VEP parameters and thyroid profile and the applied dose of L-thyroxine. There was a relationship between the level of TSH and the wave BAEP III-V interpeak latency. Conclusions. There were changes in the brain’s bioelectrical activity in one-third of the patients with HT without nervous system involvement. The increased amplitude of the VEP may indicate increased cerebral cortex activity. Disorders of the brain’s bioelectrical activity in the course of HT may be associated with an autoimmune process.

Brainstem Auditory Evoked Potentials and Visual Potentials in Kawasaki Disease: An Observational Monocentric Study

Background: Kawasaki Disease is a systemic vasculitis, particularly involving coronary arteries. Rare involvement of other vascular districts is described, as central nervous system arteries, leading to a vasculitic neuropathy. Sensorineural hearing loss and alterations of evoked potentials are uncommonly reported complications.Methods: In an observational monocentric study, 59 children (37 males; 22 females; mean age: 2.7 ± 2.2 years) with documented Kawasaki Disease were enrolled. No risk factors for hearing loss and/or neurological impairment were identified in the cohort. Brainstem auditory evoked potentials and visual evoked potentials were correlated with clinical, hamatological and radiological data, evaluated in the acute phase of the Kawasaki Disease, and during the follow-up.Results: Evoked potentials were altered in 39/59 patients (66%): of these, 27/39 (69%) showed altered IV and V waves and/or III-V interwave latencies of brainstem auditory evoked potentials; 4/39 (10%) showed pathological visual evoked potentials; 8/39 (21%) had abnormalities of both brainstem auditory evoked potentials and visual evoked potentials. No permanent deafness was reported.Conclusion: Abnormalities in visual evoked potentials were not significantly correlated with coronary artery lesions; however, the presence of abnormalities of brainstem auditory evoked potentials were associated with the risk of coronary artery lesions.

Microvascular decompression for typical trigeminal neuralgia: Personal experience with intraoperative neuromonitoring with level-specific-CE-Chirp® brainstem auditory evoked potentials in preventing possible hearing loss

Background: Permanent hearing loss after posterior fossa microvascular decompression (MVD) for typical trigeminal neuralgia (TTN) is one of the possible complications of this procedure. Intraoperative brainstem auditory evoked potentials (BAEPs) are used for monitoring the function of cochlear nerve during cerebellopontine angle (CPA) microsurgery. Level-specific (LS)-CE-Chirp® BAEPs are the most recent evolution of classical click BAEP, performed both in clinical studies and during intraoperative neuromonitoring (IONM) of acoustic pathways during several neurosurgical procedures. Methods: Since February 2016, we routinely use LS-CE-Chirp® BAEPs for monitoring the function of cochlear nerve during CPA surgery, including MVD for trigeminal neuralgia. From September 2011 to December 2018, 71 MVDs for TTN were performed in our department, 47 without IONM of acoustic pathways (Group A), and, from February 2016, 24 with LS-CE-Chirp BAEP (Group B). Results: Two patients of Group A developed a permanent ipsilateral anacusia after MVD. In Group B, we did not observe any permanent acoustic deficit after surgery. In one case of Group B, during arachnoid dissection, intraoperative LS-CE-Chirp BAEP showed a temporary lag of V wave, resolved in 5 min after application of intracisternal diluted papaverine (0.3% solution without excipients). Conclusion: MVD is widely considered a definitive surgical procedure in the management of TTN. Even though posterior fossa MVD is a safe procedure, serious complications might occur. In particular, the use of IONM of acoustic pathways during MVD for TTN might contribute to prevention of postoperative hearing loss.