Mumps virus may damage the vestibular nerve as well as the inner ear.

We report a case of mumps deafness with acute vestibular symptoms secondary to both retrolabyrinthine and inner ear dysfunction. To our knowledge, no such case has been reported elsewhere. The patient was a 6-year-old girl in whom mumps deafness was initially diagnosed. Two days after onset of the hearing impairment, severe vertigo developed. Neurotologic examinations revealed spontaneous right-beating nystagmus, left canal paresis, absence of vestibular-evoked myogenic potentials in the left ear, and absence of responses to a left galvanic body sway test (GBST). The vertigo resolved 7 days after onset. However, the left hearing impairment progressed to complete deafness. Six months later, left canal paresis was still present, but bilateral GBST responses were normal, suggesting that retrolabyrinthine vestibular function had been restored. Mumps virus may affect retrolabyrinthine function as well as the inner ear.