Is laser therapy a useful tool for treating tinnitus?

Is laser therapy a useful tool for treating tinnitus?

Jan Tunér DDS

Abstract: Low level laser therapy (LLLT) has been suggested as a treatment modality for reducing tinnitus. The scientific literature is ambiguous and the suggested treatment- and laser parameters differ considerably. Most studies have taken for granted that the target for laser therapy is the inner ear. However, it is evident that a large group of tinnitus sufferers have muscular tension in the head and neck area (somatosensory tinnitus), causing a phantom noise. If a differential diagnosis between these two groups is not performed, the outcome of any study becomes serendipity. Three double blind studies have confirmed the effect of LLLT, but without considering the somatosensory aspect, the evaluation of these studies is problematic. It could even be the case that the irradiation into the ear actually has been treating a tense masticatory muscle close to the meatus acusticus and unknowingly treated somatosensory tinnitus.

The origin of tinnitus remains controversial but it is safe to say that there is a wide array of suggestions for origin and therapeutic approaches – and all of them with limited success rate. Low level laser therapy (LLLT) has been suggested as a possible method to alleviate or cure tinnitus. This suggestion is based upon the general knowledge about the stimulating effects of coherent light. The middle and inner ear can be reached with sufficient concentrations of laser light (1) if applied via the meatus acusticus in close relation to the oval window. Early studies used very low to low doses and the results vary considerably (2-7).

Penetration of 30 mW 650 nm laser into the meatus (porcaine ex vivo sample). Courtesy M. Zazzio

A pioneer is this area is Wilden. In the late 90s he developed a new method where seemingly very high doses of infrared laser energy were applied (8). This approach has been successful and thousands of tinnitus sufferers have been improved or cured. An improvement of the actual hearing capacity, verified by audiograms, is often a positive side effect of this therapy. Irradiation into the middle and inner ear has also been successful for patients suffering from hyperacusis (hypersensitivity to sound) (9). In both cases infrared energies of 500 J per ear or more have been used. It is obvious that these high doses have no detrimental effect on the inner ear structures.

Irradiation through the meatus

The therapeutic approaches described above are based upon the assumption that the origin of tinnitus is somewhere in the inner and middle ear, prominently in the cochlea. While this is quite likely in many cases, there is a fair scientific evidence for a somatosensory connection for tinnitus as well as Meniere (10-17). This means that the origin of the noise is not coming from the ear but from overloaded muscles, predominantly in the masticatory and neck muscles. The noise is then in fact a phantom phenomenon (18, 19). Somatosensory tinnitus thus becomes a separate diagnosis requiring different therapeutic approaches than conditions located in the inner ear. The latter is still a valid hypothesis (20) but of different origin and needing different therapy.

Somatosensory laser therapy often involves the neck and trapezius areas. Courtesy Irradia AB.

The correct therapy for somatosensory tinnitus is then equilibration of the occlusion, physiotherapy, stress management and laser therapy of the involved muscles. LLLT will improve microcirculation, reduce pain and lead to muscular relaxation. One of the key muscles is the lateral pterygoid muscle (11,12,13,17). This muscle works to move the mandible into a forward motion. In cases of malocclusion, the mandibular condyle can be pushed backwards into a position close to the distal area of the bony fossa. This causes a pain reaction and a nociceptive reflex in the lateral pterygoid muscle, trying to move the condyle forwards, away from the painful area. In the end, the lateral pterygoid is exhausted, tense and painful upon palpation. Acc. to Bjorne (11,12,13), Menière and tinnitus have the same somatosensory background and the therapy is basically the same.

The lateral pterygoid muscle

It is obvious that tinnitus patients are not a homogeneous group and a differential diagnosis is mandatory before treatment. Treating somatosensory tinnitus via the meatus acusticus is not a successful approach, for obvious reasons. The diagnosis of the somatosensory group is rather straightforward, but will not be described here (read LaserWorld - TLC).

As pointed out, the amount of energy suggested for transmeatal LLLT varies considerably. In recent years, small home use devices of 650 nm diode lasers of 5 mW have been marketed and investigated. There are four double blind studies published, three with positive (21, 22, 23) and one with negative (24) results. Three positive double blind studies may seem a fair scientific justification for the therapy, and no negative effects have been reported. However, they all share the same shortcoming of not having made a somatosensory differential diagnosis of the patients involved in the studies. This means that the number of undiagnosed somatosensory patients in the study would strongly influence the outcome of the studies.

The meatus acusticus is very close to the temporomandibular joint (TMJ) and to the posterior insertions of the lateral pterygoid muscle. If can therefore be hypothesised that the laser irradiation affects the pain and inflammation in the TMJ and also relaxes the lateral pterygoid. The laser irradiation would then supress the somatosensory effect of the malocclusion during the period of laser irradiation. If this were the case, a follow up control would catch such changes. In none of the four double blind studies mentioned, such a follow up has been performed. There is some discussion about muscular relaxation techniques in one study, but not at all in the other three.

The lack of a proper diagnosis in these four studies further complicates the evaluation of the potential of LLLT in the treatment of tinnitus. From the scant literature it seems reasonable to believe that LLLT is a viable and safe method, but the optimal parameters are far from resolved. On the other hand, the literature support for a somatosensory background is stronger.

The additional effect of LLLT for somatosensory patients is not scientifically documented at all. The rationale here has so far to be taken from other studies where LLLT has been proven to be of great value for pain, inflammation and trismus (25-40). LLLT is an adjunct therapy that makes the healing faster, but the traditional modalities such as occlusal adjustment and physiotherapy must come first.

Tinnitus is a frequent condition and can have a very negative influence on the quality of life. There are many suggested therapies but none very effective, most of them aiming at “coping” rather than “curing”. The absence of objective diagnostic tools and the lack of knowledge about the mechanisms explain the vast number of suggested therapies. Under such circumstances, it is important to be open for new theories.

Curing or reducing somatosensory tinnitus requires cooperation between ENT specialists, dentists and physiotherapists. A common problem is that the patient will not inform a dentist about the tinnitus (because he/she is supposed not to have anything to offer) and the ENT doctors are seldom aware of the somatosensory connection.

The differential diagnosis remains of central importance. Indeed, irradiation into the ear has been further supported by a recent study by Rhee et al (41) where LLLT improved the survival rate of cochlear hair cells after gentamycin-induced ototoxicity. But it is obvious that the origin of tinnitus is not solely found in the ear.

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