Auditory test result characteristics of subjects with and without tinnitus.

INTRODUCTION Chronic tinnitus is the persistent sensation of hearing a sound that exists only inside the head. It is the result of abnormal neural activity within the auditory system and has been referred to as a "phantom auditory sensation" [1]. Epidemiology studies reveal that between 10 and 15 percent of all adults experience chronic tinnitus [2-7]. The Veterans Health Administration (VHA) regards tinnitus as a disabling condition. U.S. military veterans with service-connected disabilities may receive a monetary benefit as compensation. The basis for awarding a tinnitus disability is that the tinnitus is (1) at least recurrent (intermittent) and (2) related to military service [8-9]. The number of tinnitus disability claims has increased dramatically during this decade (Figure 1). As of October 2008, 558,232 veterans had been awarded tinnitus service-connection disability. * Among veterans returning from the Iraq and Afghanistan wars, tinnitus is the most common service-connected disability (67,689 veterans in 2008). These concerns have prompted our overall effort to develop tests that can help ensure that a tinnitus disability is accurately rated and that allow for reexamination whenever a need exists to verify the continued existence of tinnitus. The current study is part of that overall effort. [FIGURE 1 OMITTED] Special audiological tests are effective in detecting deliberate exaggeration of hearing loss [10-11], but no documented test exists that is capable of detecting the presence or absence of tinnitus. Vernon developed the "two dB rule," which involves matching the loudness of tinnitus to tones five or six times during a test session [12]. According to Vernon's rule, the presence of tinnitus is indicated if the repeated results within a session agree to within 2 dB (provided the loudness matches [LMs] are obtained with 1 dB resolution). Jacobson et al., however, reported results from an experiment that showed test-retest reliability of LMs to be similar between individuals with and those without tinnitus [13]. The only difference was that individuals without tinnitus generally provided LMs at higher levels. Any type of audiometric test for tinnitus diagnosis may rely at least partly upon the demonstration of response reliability. That is, the validity of any response depends upon its reproducibility; thus, response reliability is expected to be an important component of any test developed to assess the presence of tinnitus for claims purposes. Because so many parameters of tinnitus are capable of being measured, any of those parameters could potentially be used for repeated testing to evaluate a tinnitus claim. The key is to determine which test, or combination of tests, will be most effective in accomplishing this purpose. Tinnitus loudness matching has been shown to be very reliable with tinnitus patients, but the Jacobson et al. study suggests that loudness matching alone may be of very limited value in distinguishing individuals with versus those without tinnitus [13]. Tinnitus loudness matching can be expanded to obtain LM functions, i.e., LMs at a series of audiometric frequencies. When tested in this manner, patients reveal characteristic patterns of responses [14]. Individuals with tinnitus, regardless of the perceived pitch of their tinnitus, have been shown to produce high agreement of tinnitus LMs across multiple presentations at 1/3-octave intervals between 1 and 16 kHz [15]. Thus, an entire LM function is generally reliable when tinnitus is present. We completed a pilot study to investigate the potential for LM functions to detect differences between 12 subjects with tinnitus versus 12 subjects without tinnitus [16]. Testing was done using a computer-automated program that had recently been modified to allow more patient control of test stimuli (through the use of a handheld control pad device). Procedures that were performed in that study involved self-selected hearing thresholds and tinnitus LMs at frequencies between 1 and 16 kHz (in 1/3-octave intervals). …