Tone decay test

Anatomy of the Human Ear

Tone decay test graphical

Tone Decay Test is a specialized audiometry test used in the field of audiology to assess the ability of the auditory system to sustain hearing sensitivity over time. This test is particularly useful in identifying abnormalities related to the auditory nerve and central auditory pathways, which may not be detected through standard pure-tone audiometry tests.

Overview

The Tone Decay Test measures the ability of an individual to maintain perception of a continuous pure tone at the threshold level over a specified period. The test is typically conducted using audiometer headphones, where a tone is presented to the ear at the threshold level of hearing for that frequency. The duration for which the individual can perceive the tone before it "decays" or becomes inaudible provides insight into the integrity of the auditory system, particularly the auditory nerve and higher auditory pathways.

Procedure

The procedure for the Tone Decay Test involves presenting a continuous pure tone at the threshold level to the test ear. The tone is usually presented for a period of 60 seconds, and the patient is instructed to indicate when the tone is no longer audible. If the tone becomes inaudible, the intensity is increased by 5 dB and presented again until the patient can hear the tone for the full duration. The amount of increase in intensity required to maintain audibility of the tone for 60 seconds is recorded as the tone decay.

Clinical Significance

The Tone Decay Test is significant in diagnosing and differentiating between sensorineural hearing loss related to cochlear pathology and that originating from the auditory nerve or central auditory pathways. A positive tone decay, where significant increase in intensity is needed to maintain audibility, suggests retrocochlear pathology such as acoustic neuroma or other neural abnormalities. In contrast, minimal to no tone decay is typically observed in normal hearing individuals or those with cochlear hearing loss.

Limitations

While the Tone Decay Test provides valuable information about the auditory system's function beyond the cochlea, it has limitations. The test is subjective, relying on patient response, which can be influenced by attention, understanding, and cooperation. Additionally, the test does not specify the exact location of the pathology within the auditory nerve or central auditory pathways.

Conclusion

The Tone Decay Test is a useful tool in the audiological assessment, particularly for identifying auditory system abnormalities beyond the cochlea. It complements other audiometric tests to provide a comprehensive evaluation of hearing function and pathology.