Audiometric comparison of Lassa fever hearing loss and idiopathic sudden hearing loss: evidence for viral cause.

A recently published prospective study on acute sensorineural deafness in Lassa fever among a West African population showed the audiometric pattern of a known virally induced hearing loss. Using the audiometric data from the patients with Lassa fever in that study, we analyzed and classified the initial hearing loss and final recovery into three groups by pure-tone average values and then did the same for 222 patients with idiopathic sudden hearing loss (SHL) in our study. Statistical analyses of the severity of initial hearing loss and the hearing recovery pattern indicate that the clinical course of our 222 patients with idiopathic SHL showed no statistically significant differences from the clinical course of the patients with Lassa fever. We found a marked difference in age, however, and a clinically significant difference in the incidence of bilateral hearing loss. In reviewing the literature on sudden sensorineural hearing loss, we found no apparent relation between severity of viral illness and initial hearing loss or subsequent recovery. Cummins et al. suggest that virally induced hearing loss in Lassa fever is linked to the host's immune response and not to the viremia. We thus propose a virally induced immune response mechanism for idiopathic sensorineural SHL. Further prospective studies are needed for verification.