Vestibular function in acoustic trauma

Histological and functional derangement of the vestibular system has been reported in laboratory animals exposed to high levels of noise. However, reports of clinical series give contradictory results with regard to vestibular disturbances in industrial workers and military personnel suffering from noise-induced hearing loss (NIHL). This study evaluates vestibular function in 22 men with documented NIHL and in 21 matched controls, using electro-nystagmography (ENG) and the smooth harmonic acceleration (SHA) test. There was a significantly lower vestibulo-ocular reflex gain (p = 0.05), and a tendency towards decreased caloric response in the patients. There were no differences between patient and control groups in: incidence of vertigo and of spontaneous, positional and positioning nystagmus; directional preponderance and canal paresis in the ENG; or in phase and asymmetry parameters in the SHA test. These results demonstrated a symmetrical, centrally compensated decrease in vestibular end-organ response associated with symmetrical hearing loss in the patients. Statistically significant correlations were found between average hearing loss, and decrease in average vestibulo-ocular reflex gain (p = 0.01) and ENG caloric lateralization (p = 0.02). These correlations might indicate a single mechanism for both cochlear and vestibular NIHL. The results imply subclinical, well compensated malfunction of the vestibular system associated with NIHL.