Customized Sound Therapy (CST) is a technology that provides therapy through the use of a high-fidelity and accurately produced replica of the patient's tinnitus for tinnitus patients having low to moderate distress levels. The tinnitus replica itself is played as the “missing input” to the auditory system to reduce its overall gain.
Most patients with chronic bilateral tinnitus have a tinnitus sensation that is a single sound, typically with a center frequency above 3000 Hz.1 The sound sensation is rarely a pure tone, but can commonly be matched to a center frequency with a narrowband noise on the order of 0.1% around it. The center frequencies are above the human speech range and are the frequencies found in the noise notch from noise-induced hearing loss or in the high-frequency hearing range above 8000 Hz that the audiologic community is now attending to.
The mainstay initial treatment for tinnitus is sound.2 Sound enrichment should be considered for most tinnitus patients. Most patients in clinical practice volunteer that their tinnitus (and their overall well-being) is better when they are outdoors. Buildings act as low-pass filters and tend to suppress high frequencies. Outside we get the full auditory range of frequencies. Is tinnitus, therefore, a “nature-deficit disorder”? Perhaps, but it is primarily a disorder of sound sensation.
Our overall approach to tinnitus is based on the belief that the specific sound sensation a patient experiences is an indication of the type of failure in the auditory system that causes it. With hearing loss, recruitment or increase in gain occurs in the higher auditory pathways, brainstem, colliculus, thalamus, and cortex. Given the common matching of tinnitus sensations with a narrow band surrounding a center frequency, a strong likelihood is that a single tonotopic pathway is overactive in tinnitus.
An analogy useful to patients is a bad piano key (see Figure 1). Through the loss of signal inputs from the peripheral auditory system, gain increase has propagated through the auditory system and baseline activity has increased in the auditory cortex. The threshold where activity represents a perceptible sound is reached with one pathway. Note that some patients have multiple tinnitus sensations, which represent multiple overactive pathways.
For patients with no more than moderate hearing loss, therapy with sound is a means of supplying the missing signal to the overactive auditory cortex. By having patients spend time outdoors or wear noise generators or hearing aids that do not roll off below 10,000 Hz, it is possible to randomly stimulate the pathways that have low inputs and increased gain. However, few, if any, hearing aids or noise generators can achieve this bandwidth.
Customized Sound Therapy (CST) addresses the tinnitus percept such that the missing input can be reliably provided for intervals that will be rapidly therapeutically effective. By supplying the missing sound via a tinnitus replica, neuroplastic processes can alter the activity of the auditory percept circuits and provide relief from tinnitus in weeks.3
SELECTION OF PATIENTS
The key to success with CST is patient selection. Patients with severe psychological distress are not appropriate for management with sound, CST or otherwise. Patients with anxiety, depression, and, particularly, suicidal ideation need immediate medical psychological intervention.
All practitioners who see patients with tinnitus are confronted with distressed patients, and these people deserve immediate attention. One means of assessing distress is to use a validated questionnaire that a patient can fill out rapidly. Such questionnaires include the Tinnitus Handicap Inventory (THI) and the Tinnitus Reaction Questionnaire (TRQ). Patients indicate their distress on the written form and the scores are accumulated into a total. A high score, e.g., above 50 on the THI, indicates that a patient is in severe distress and requires focused intervention.
Fortunately, many patients with tinnitus experience mild or moderate distress. Providing CST in such instances is straightforward. A medical evaluation of a patient's hearing and tinnitus is required, with a history and audiogram. Patients with potential medically induced causes need appropriate referrals. Subjects should then be counseled regarding the character of their tinnitus. Patients with a variable tinnitus frequency and, in particular, pulsatile tinnitus need medical referral for evaluation of possible ongoing disorders of the cochlea, auditory nerve, or higher auditory centers. If the patient describes a constant tinnitus sound, then CST can be attempted. Variable intensity of the sound is acceptable and is common.
CST SOFTWARE USE
To provide Customized Sound Therapy, the practitioner needs the CST software and a sound player. Otosound LLC produces both the software and a sound player. The software has a specially designed, copyrighted interface that is similar to an audiometer and that practitioners will find intuitive to use (see Figure 2). However, unlike an audiometer, the CST software has full digital sound from 20 to 20,000 Hz at 1-Hz resolution.
The interface has three identical sound panels that can be used to present sounds rapidly to the patient. Based on the initial interview, some sample sounds can be presented to the patient. The traditional “two-alternative forced-choice” process is used. Typically, the center frequency of the tinnitus is identified first. Note that sometimes an octave mismatch can occur, so frequencies an octave above and an octave below a possible center frequency should be tested.
Once a reliable center frequency is identified, narrow-band noises can be introduced. The bandwidth can be readily varied for an appropriate match to the patient. A center frequency and a narrow band noise usually result in a match that patients indicate is reliable. In our experience, we have matched tinnitus sensations from a few hundred Hz all the way out to 19,000 Hz. Based on the theory described above, our therapeutic approach is one where the therapeutic sound is a replica of the tinnitus sensation.
On the interface, the lower part is a mixing panel where multiple sounds can be added. They can be balanced with appropriate relative volumes through the volume controls above. Calming or soothing sounds can be added, particularly for patients with hyperacusis. There is a library of such sounds included (described below). Once a final selection is made, the “Save to PSP” button is pressed and the sound file is stored in memory.
THE CST PLAYER
A high-fidelity player is essential for CST. In particular, full digital sound out to 20,000 Hz should be provided. The personal sound player (PSP) made by Otosound provides this and other important features. With the CST software connected via a USB cable to the PSP, the player acts as a “sound card.” In other words, the actual electronics that the patient will take home are the source of the test and therapeutic sounds. The CST software commands the digital sound to be produced, and the PSP plays it. Further, the PSP has two independently driven sound outputs.
Patients listen to the sounds with the earphones that they take home. Once the therapeutic sound is created, the sound file is stored in the sound player's memory and the player is disconnected from the computer. The PSP is rechargeable and runs on its own when disconnected from the CST host computer.
It is very simple to use, and the patient does not have to manage menus. One big button turns the sound on and off. There are two volume controls, left and right, each with 0.5-dB step volume increments. The fine resolution in volume control is used for therapy management. A simple display shows if the player is off, playing, or charging.
The memory of the PSP contains a usage log system. When it is turned on, the time and volume settings of the player are logged every 3 minutes. When the unit is re-attached to the CST software host computer, the usage log is captured by the CST software where the practitioner can review it to understand the patient's use patterns.
Mixing of sounds is performed in the lower part of the CST interface. The earphones must have a flat frequency out to 20,000 Hz. Further, the earphones must not occlude the ears. Reduced hearing input is the cause of tinnitus and occlusion could potentially make it worse. Further, occlusion makes using the CST system more difficult as patients cannot hear what is going on around them. Currently, we have found the Bang and Olufsen™ A8 earphones to have the characteristics we need.
Usage for patients is straightforward. They are instructed to listen to the therapeutic sound for a total of 2 to 3 hours a day. Continuous or all-day use is not necessary. Importantly, the system is not used as a masker. The therapeutic sound is played at a volume where the patient can hear the tinnitus and the therapeutic sound at the same time. Note that for safety purposes, the output of the system is limited to 80 dB SPL. The patient should be able to hear the therapeutic sound in a quiet environment, such as an office. As the tinnitus sensation changes, the relative volume of the sound output can be managed with the volume controls.
We have tested the CST system in our laboratories.3 In addition, an independent clinical test was carried out by the Otolaryngology Department (ORL) and the Audiology Unit of the Fondazione IRCCS Cà Granda Ospedale Maggiore Policlinico, a busy tinnitus clinic in Milan, Italy.
Subjects were selected to have THI scores of less than 50 and had no exclusion factors such as concomitant drug treatment. The instructions as outlined above were provided. Thirty-eight subjects with chronic tinnitus were selected from the clinic population. CST was administered to a group of 19 subjects and a simple white noise to a group of 9 subjects. Tinnitus Handicap Inventory (THI) and visual analog scale (VAS) scores were obtained pre- and post-therapy and at follow-up at 3 months. The results were compared with a group of 10 subjects who underwent Tinnitus Retraining Therapy (TRT) for 3 months. Subjects were randomly assigned to therapy, control, and TRT groups.
The results from the 16 subjects who completed CST treatment (3 dropped out before the end of the therapy) showed significant improvements in THI and VAS score for the tinnitus life effect after 8 weeks of CST therapy. The improvement was maintained at 3 months follow-up even after CST therapy was discontinued. In the control group only the VAS score for the annoyance of tinnitus showed a significant decrease. The TRT group showed a significant decrease in both THI and VAS for annoyance.
The initial and follow-up results were presented at the Tinnitus Research Initiative (TRI) annual meetings in 2009 and 20104,5 and are being prepared for publication. Other labs are assessing CST at this time, though no formal clinical trials have yet been carried out.
COUNSELING AND CONTRA-INDICATIONS
While psychological counseling is a common method of therapy for tinnitus patients, it is not a part of CST. The test done in Milan shows that counseling (other than instructions on player use) is not necessary when treating patients with low-level tinnitus (THI scores less than 50).
As described above, high tinnitus distress scores mean that patients should be reviewed for medical and psychological management of their tinnitus. Sound therapy alone is not appropriate for these patients. Importantly, if CST (or any sound therapy) exacerbates a patient's tinnitus or increases distress, the therapy should be immediately discontinued. Also, if patients cannot hear the therapeutic sounds, another modality must be used.
Otosound LLC is developing refinements to its technologies. These refinements include cortical evoked potential markers of the presence of tinnitus and use of these markers for identification of therapeutic sounds. Further, the CST platform will be ported to a wireless-based, high-fidelity sound system for broad dissemination.