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Henrique F. Pauna MD | Renata M. Knoll MD | Rory J. Lubner | Jacob R. Brodsky MD | Sharon L. Cushing MD, MSc | Miguel A. Hyppolito MD, PhD | Joseph B. Nadol Jr MD | Aaron K. Remenschneider MD, MPH | Elliott D. Kozin MD
Abstract
Objective: While cochlear ossification is a common sequela of meningitic labyrinthitis, less is known about the effects of meningitis on the peripheral vestibular end organs. Herein, we investigate histopathologic changes in the peripheral vestibular system and cochlea in patients with a history of meningitic labyrinthitis.
Methods: Temporal bone (TB) specimens from patients with a history of meningitis were evaluated and compared to age-matched controls. Specimens were evaluated by light microscopy and assessed for qualitative changes, including the presence of vestibular and/or cochlear endolymphatic hydrops, presence and location of inflammatory cells, new bone formation, and labyrinthitis ossificans; and quantitative changes, including Scarpa's ganglion neuron (ScGN) and spiral ganglion neuron (SGN) counts.
Results: Fifteen TBs from 10 individuals met inclusion and exclusion criteria. Presence of inflammatory cells and fibrous tissue was found in 5 TBs. Of these, evidence of labyrinthitis ossificans was found in 2 TBs. In the peripheral vestibular system, mild to severe degeneration of the vestibular membranous labyrinth was identified in 60% of cases (n = 9 TBs). There was a 21.2% decrease (range, 3%-64%) in the mean total count of ScGN in patients with meningitis, compared to age-matched controls. In the cochlea, there was a 45% decrease (range, 25.3%-80.9%) in the mean total count of SGN compared to age-matched controls (n = 14 TBs). Conclusions: Otopathologic analysis of TBs from patients with a history of meningitic labyrinthitis demonstrated distinct peripheral vestibular changes. Future research may help to delineate potential mechanisms for the observed otopathologic changes following meningitis.
Level of Evidence: N/A
INTRODUCTION
Meningitis is a major cause of mortality and morbidity worldwide. It is estimated that the incidence of bacterial meningitis is about 0.8-2.6 per 100,000 adults in developed countries. The most common causative microorganisms are the Haemophilus influenzae type B (Hib), Streptococcus pneumoniae, and Neisseria meningitidis. The overall incidence of bacterial meningitis as well as its morbidity has decreased due to the introduction of vaccines, implementation of effective antibiotic and steroid therapy, and modern intensive care facilities. Despite improved outcomes, meningitis remains an important public health issue, especially in developing nations. Worse, it can increase its incidence and transmissibility when families decide not to vaccinate their children.
Sensorineural hearing loss (SNHL) may affect up to 54% of survivors following meningitis. Likewise, vestibular dysfunction also occurs frequently and is nearly universal in those with SNHL. Previous otopathological studies have suggested that SNHL following meningitis occurs due to the spread of the infection from the meninges to the labyrinth via three routes, including (a) the cochlear aqueduct and the cochlear modiolus (meningogenic), (b) the vascular support of the inner ear (hematogenic), or (c) the oval and round windows (tympanic routes). Once in the labyrinth, inflammatory mediators may induce severe labyrinthitis and disrupt the blood-labyrinth barrier, resulting in hearing and vestibular loss.
Despite research on peripheral auditory pathway damage, few studies have examined the peripheral vestibular system following meningitis. It is estimated that 15% to 85% of children with SNHL following meningitis present with associated vestibular dysfunction. Zingler et al reported bilateral vestibular dysfunction in 11% of patients with dizziness, in which 5% of the cases were caused by meningoencephalitis. Symptoms of vertigo and dizziness may not be the best measures of the true prevalence of vestibular dysfunction following meningitis. Using objective assessments of vestibular end-organ testing, including horizontal canal function as measured by caloric stimulation, high-frequency rotation, and otolithic function as measured by vestibular evoked myogenic potential (VEMP), Cushing et al also demonstrated that vestibular function was compromised in children with SNHL after meningitis. These vestibular end-organ deficits translated functionally into poor balance skills in this cohort. Likewise, children with SNHL and vestibular and balance impairment due to meningitis who were rehabilitated with cochlear implants also demonstrated a higher rate of cochlear implant failure. In an additional study, the poor cochlear implant performance was hypothesized to be due to their vestibular and balance impairments.
To date, no otopathology study has systematically evaluated peripheral vestibular changes following meningogenic labyrinthitis. The specific aims of the paper are to (a) describe the histopathologic changes in the human inner ear in cases of meningitis, and (b) correlate pathologic changes within the vestibule and the cochlea.
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