An enlarged vestibular aqueduct, high frequency hearing loss, and fluctuating hearing loss are characteristics of enlarged vestibular aqueduct syndrome. Causes of fluctuating hearing loss include contusion or extreme movement of the head. In addition, mutations in the PDS gene have been reported as responsible for this condition.
Case 1 began to have fluctuating hearing loss after a contusion in September 1999.After a decrease in hearing ability in the right ear in July 2001, recovery was not seen. However, two years and four months later, hearing recovery occurred suddenly.
Case 2 began to have fluctuating hearing loss after a school athletic event in May 1998. After a decrease in hearing ability in the left ear in July 2003, immediate recovery was not seen but hearing was regained gradually over an eight-month period. Hearing loss was seen in the right ear in November 2004 and recovery occurred four months later.
Fluctuating hearing is thought to be caused by the backward flow of low potassium fluid from the endolymphatic sac, following a sudden increase in pressure on the brain. The lowered potassium of the endolymphatic fluid contributes to a lowered endocochlear potential that causes the hearing impairment. On the other hand, it has been reported that in PDS gene knockout mouse, the expression of KCNJ 10, which is a potassium channel in the stria vascularis, is lacking and there is a markedly lowered voltage of endocochlear potential, suggesting that the inhibition of KCNJ10 is involved in hearing loss. Accordingly, the current two cases, in which long-term hearing impairment gradually or suddenly recovered, suggest that acute hearing impairment is not due to damage of the hair cells.
