Clinical and Scientific Aspects of Tinnitus

Over the past 15 years, we have received numerous phone calls and e-mails from tinnitus patients desperately seeking a cure for disabling or persistent tinnitus. Sometimes we receive only one call from a patient, but occasionally a patient keeps calling back for weeks or months looking for a scientific breakthrough that never seems to come as quickly as mysteries are solved on CSI, the TV criminal series. Several common themes have emerged from interactions with these patients: (1) “I have a roaring sound in my ear or head, but my family and friends don't believe me and think I've become mentally unstable. What can I do to convince them that tinnitus is a real problem?” (2) “I spoke to my doctors or audiologist and he [or she] says nothing can be done to treat my tinnitus, and I need to learn to live with it for the rest of my life.” (3) “I read you were doing research on tinnitus. Have you found out what causes it yet?” (4) “When do you think you will find a cure? What's taking so long? Can I call you back in 6 months?”

What can you tell the desperate tinnitus patient who calls you? The series of scholarly review articles in this and the following issue of Seminars in Hearing will bring you up to date on many of the scientific and clinical advances in tinnitus and help you address these difficult questions.

They say a picture is worth a thousand words, and when it comes to proving to friends and family that tinnitus really exists, patients and clinicians can turn to the remarkable pictures of tinnitus that have emerged during the past decade from sophisticated brain-imaging studies of tinnitus conducted with positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG). The neural generators responsible for tinnitus, once relegated to the cochlea, may actually reside at higher levels of the auditory pathway in the brain. So the answer to the first question is yes; tinnitus is real. We can “see it” and measure it with modern imaging techniques, and in some patients the neural generator is in the brain.

We don't have a magic pill that will abolish the phantom sound of tinnitus in 100% of patients, but clinicians who tell a patient that nothing can be done are just plain wrong! Sound therapy combined with education and counseling is extremely successful in reducing the anxiety, worry, and stress associated with severe and disabling tinnitus and hyperacusis. Many audiologists and some physicians, reluctant at first, have begun to adopt this approach. Tinnitus generally does not go away completely but it subsides, and patients are able to manage, largely ignore, or tune out the phantom sound. In addition to sound, novel stimulation approaches to treating tinnitus involve transcranial magnetic stimulation (TMS) of brain regions, which often leads to short-term or long-term reduction of the tinnitus percept.

The etiology of tinnitus is often associated with damage to the sensory cells in the inner ear. Such damage invariably reduces the flow of neural activity from the inner ear to the brain, and this lack of cochlear input is hypothesized to cause aberrant neural activity in central auditory structures that gives rise to tinnitus. Cochlear implants, which deliver electrical pulses to the cochlea, reactivate the quiescent auditory nerve fibers and not only restore hearing, but in most cases they partially or completely suppress tinnitus. When the implant is turned off, the tinnitus reemerges within minutes or hours. Like sound stimulation, electrical stimulation of damaged ears may develop into an effective method of suppressing tinnitus.

Which drugs can reliably suppress tinnitus? Case reports and open label studies with small groups of patients often turn up promising leads, but which drugs really work and which do not can only be ascertained through carefully controlled clinical trials with large groups of patients. Overall outcomes from large clinical trials must be scrutinized carefully, for it may turn out that no one drug will be effective in all patients. It may be that only a small “special” group of tinnitus patients responds to a particular drug therapy while others do not. Identifying these subgroups of drug responders remains an important area of clinical research.

Rapid advances in modern clinical medicine have often come about from the development of animal models of a disease or disorder. Since the groundbreaking work of Jastreboff in the 1980s, several laboratories throughout the world have developed animal models that can “tell us” from their behavior if the animals are experiencing tinnitus. The development of these behavioral models of tinnitus have allowed researchers to correlate behavioral measures of tinnitus with neurophysiological, neurochemical, biochemical, and molecular indexes that may eventually tell us what is triggering these phantom sounds.

Tinnitus was once considered an intractable or impossible area to research effectively, but new tools and techniques have given scientists renewed hope for discovering what causes tinnitus. Unlike CSI, the scientific mystery for the causes of tinnitus may take a decade or more to unravel, but a look through the scientific rearview mirror shows that much progress has been made in the past two decades. Clinicians now have some useful techniques and approaches to treat tinnitus patients and can offer hope to the desperate tinnitus patient.