TRANSIENT DEAFNESS DUE TO TEMPERATURE-SENSITIVE AUDITORY NEUROPATHY

Objective: To define mechanisms accounting for transient deafness in t hree children (two siblings, ages 3 and 6, and an unrelated child, age 15) when they become febrile. Design: Audiometric tests (pure-tone au diometry, speech and sentence comprehension), tympanometry, middle ear muscle reflex thresholds, otoacoustic emissions (OAEs), and electroph ysiological methods (auditory brain stem responses [ABRs], sensory evo ked potentials, peripheral nerve conduction velocities) were used to t est the children when they mere afebrile and febrile. Results: ABRs, w hen afebrile, were abnormal with a profound delay of the IV-V and abse nce of waves I-III. The ABR in one of the children, tested when febril e, showed no ABR components. Measures of cochlear receptor function us ing OAEs were normal in both febrile and afebrile states. Cochlear mic rophonic potentials were present in the three children, and a summatin g potential was likely present in two. When afebrile, there was a mild threshold elevation for all frequencies in the 15-yr-old and a mild e levation of thresholds for just low frequencies in the two siblings. S peech comprehension in quiet was normal but impaired in noise. One of the siblings tested when febrile had a profound elevation (>80 dB) of pure-tone thresholds and speech comprehension was absent. Acoustic ref lexes subserving middle ear muscles and olivocochlear bundle were abse nt when febrile and when afebrile. No other peripheral or cranial nerv e abnormalities were found in any of the children. Sensory nerve actio n potentials from median nerve in one of the children showed no abnorm alities on warming of the hand to 39 degrees C. Conclusion: These chil dren have an auditory neuropathy manifested by a disorder of auditory nerve function in the presence of normal cochlear outer hair cell func tions. They develop a conduction block of the auditory nerves when the ir core body temperature rises due, most likely, to a demyelinating di sorder of the auditory nerve. The auditory neuropathy in the two affec ted siblings is likely to be inherited as a recessive disorder.