Somatosensory Tinnitus: Neurophysiological Considerations & Treatment Options

Tinnitus affects 50 million people in the United States alone.^1-4 It is defined as “the conscious perception of an auditory sensation in the absence of a corresponding external stimulus”.⁵ While tinnitus can be classified into a number of different categories,⁵ the primary focus of this article is somatic or somatosensory tinnitus (ST).⁶ ST is associated with an auditory disturbance related to an ipsilateral somatic disorder of the head or upper neck in the absence of other hearing complaints and/or abnormal findings on neurologic exam.⁷ Oostendorp et al recently reported clinical criteria for the diagnosis of ST, to include (1) neck pain; (2) impairment of cervical AROM, preferably rotation; (3) modulation of tinnitus by head and neck movements and/or posture; and (4) tenderness of cervical-occipital muscles.⁸ Notably, some of these criteria overlap with the diagnostic criteria for cervicogenic headache and/or cervicogenic dizziness.⁸

PHYSICAL THERAPISTS ARE KEY TO DIAGNOSIS & TREATMENT OF SOMATOSENSORY TINNITUS

Both primary and secondary somatic sensory neurons of the dorsal root ganglia and the trigeminal ganglia (a.k.a. the trigeminocervical nucleus), have connections with the auditory system.⁹ More specifically, the cochlear nuclei receive primary projections from ophthalmic and mandibular centers of the trigeminal ganglia and the C2 dorsal root glanglia.^{9, 10} The cochlear nerve and the inferior colliculus also receive secondary projections from the spinal aspect of the trigeminal nucleus and the nuclei of the dorsal column medial lemniscus pathway.^{9, 11} Given the convergence of the dorsal horns at C1-C3 and the spinal aspect of the trigeminal nucleus, afferent pain information from the upper neck can propagate excessive and/or aberrant information to the cochlear nerve and inferior colliculus.¹² Thus, added stimulation from the trigeminal ganglia, the dorsal root ganglia and/or the dorsal column may alter the firing rates of neurons in the cochlear nuclei and inferior colliculus.^{7, 9} While the addition of spontaneous neural activity from “nonsound driven” sources may increase the loudness (or intensity) of tinnitus, an alteration of neural synchrony could account for changes in pitch associated with tinnitus.⁹ According to Sanchez et al, the most important aspect of somatosensory tinnitus is that it is typically related to problems of the head and neck rather than the ear, and as a result, dentists and physical therapists should play a key role in the diagnosis and treatment strategy.¹³

In this regard, it is perhaps worth noting that there is a strong neurophysiologic relationship between ear, jaw and facial muscles. For example, clinching due to over activation of the trigeminal nerve may stimulate the levator fibers of the medial pterygoid muscle, thus affecting the tensor veli palatini via the interposed fascia.¹⁴ This may further alter the intratympanic pressure of the Eustachian tube and change the tympanic membrane tension via the tensor tympani muscle,¹⁵ leading to tinnitus.¹⁴ In addition, besides the medial ptyergoid, the tensor veli palatini is the only muscle of the palate that is innervated by the medial pterygoid nerve, a mandibular branch from the trigeminal nerve.¹⁶ As such, trigeminal over activation may directly impact the auditory system via the tensor veli palatini.¹⁶ Notably, there is an increased prevalence of tinnitus in patients that suffer from somatoform disorders,¹⁷ dental conditions,¹⁸ temporomandibular dysfunction (TMD)^{9, 19, 20} and craniocervical imbalances.^21,22

UPPER CERVICAL MANIPULATION AND ACUPUNCTURE FOR SOMATOSENSORY TINNITUS

Limited evidence suggests that conventional physical therapy can have a positive effect on ST.^{13, 23} According to Michiels et al, multimodal physical therapy targeting the cervical spine can help improve symptoms related to tinnitus.²⁴ Oostendorp et al further recommended a combined approach consisting of physical therapy and education for ST and tinnitus-related sensitization.⁸

In a multinational review article of self-reported non-musculoskeletal responses to cervical manipulation, Leboeuf-Yde et al reported a number of patients with decreased ringing in their ears. Moreover, non-musculoskeletal improvements were most often reported with high-velocity, low-amplitude thrust manipulations targeting the upper cervical spine.²⁵ In addition, a number of case studies also support the use of cervical manipulation for the treatment of tinnitus.^{26, 27} The overlap in the diagnostic criteria and neurophysiologic mechanisms between ST, cervicogenic headaches (CGH) and TMD (i.e. the trigeminocervical nucleus) further suggests that upper cervical manipulation may be appropriate for somatic tinnitus.^{28, 29} Nevertheless, while upper cervical spinal manipulation has been found effective in patients with CGH³⁰ and TMD,^{28, 29} only a single case study has been reported on the successful use of spinal manipulation in the management of a patient with ST, CGH and TMD.²⁶

Bezerra-Rocha et al found significantly more trigger points in the splenius capitis, sternocleidomastoid, temporalis, trapezius, scalenus and infraspinatus in patients with tinnitus as compared to patients without tinnitus.³¹ The trigger points corresponded with the same side of the body as the tinnitus symptoms, and temporary modulation of the tinnitus was experienced with digital pressure to these muscles.³¹ Notwithstanding these findings, there is still a paucity of studies that have attempted to investigate the modulation of tinnitus related symptoms via intramuscular trigger point dry needling.

Notably, the 2014 clinical practice guidelines for tinnitus made no recommendation regarding the use of acupuncture for tinnitus;³² likewise, the latest systematic review by He et al found no high quality studies to support the use of acupuncture for tinnitus.³³ However, a number of case studies^{34, 35} and more recent RCTs^{22, 36} appear to suggest otherwise. Low et al found electroacupuncture did not provide increased benefits to patients with somatic vs. nonsomatic tinnitus.²² Importantly, however, patients in the somatic tinnitus group that reported symptom modulation with forceful muscle contraction maneuvers demonstrated a favorable response to electroacupuncture.²² The patients received a single treatment of electroacupuncture at the following acupoint locations: GB8 (1.5 cun above the apex of the ear within the temporalis muscle), TE19 (immediately posterior to the ear within the temporalis muscle and level with the inferior orbit of the eye), TE17 (posterior to the lobule of the ear, in the depression between the angle of the mandible and the mastoid process, within the proximal sternocleidomastoid muscle at the level of C1), TE21 (in the depression anterior to the supra-tragus notch on the posterior border of the mandibular condyle, immediately inferior to  the zygomatic arch but superior to SI19), GB2 (peri-articular capsule of posterior TMJ, inferior to TE21 and SI19), ST7 (below the zygomatic arch within the mandibular notch, within the deep masseter and lateral pterygoid muscles) and GV20 (center of the top of the head, midpoint between the apex of the ears, within the aponeurosis that connects the frontalis and occipitalis muscles).  The investigators manually stimulated the needles to achieve a de qi response (i.e. a deep pressure, dull ache, heaviness, distention or warmth) and left the needles in situ for 30 minutes with low-grade electricity set to 100 Hz.²²

Regarding the optimum dosage, Marks et al reported a minimum of 2-weeks of acupuncture was required to effectively manage somatosensory tinnitus.³⁷ In another study, patients reported significant improvements in the intensity of tinnitus symptoms and quality of life following 10 sessions (40-minute treatments twice per week over 5 weeks) of electroacupuncture compared to the control group.³⁶ Notably, patients were needled with electric stimulation bilaterally, 1.5 cm above the apex of the ear along a 4 cm horizontal line within the temporalis muscle known as the vestibulocochlear line.³⁶ Given the neurophysiological connection between tinnitus and TMD, and the evidence supporting the use of acupuncture for TMD,^{38, 39} it follows that needling strategies targeting the muscles of mastication, particularly the medial pterygoid,¹⁴ might also be useful for the treatment of ST.

CONCLUSION

Given the primary and secondary neural projections from the craniocervical centers of the brainstem to the cochlear nerve and inferior colliculus, and the findings of  recent randomized controlled trials, upper cervical manipulation, electroacupuncture and/or electrical dry needling may be effective for the treatment of somatosensory tinnitus.

AUTHORS

Aaron Womack, PT, Cert. DN, Cert. SMT, Dip. Osteopractic
Clinical Manager, Alliance Health Midwest Rehab., Midwest City, OK
Fellow-in-training, AAMT Fellowship in Orthopaedic Manual Physical Therapy

Raymond Butts, PhD, DPT, MSc (NeuroSci), MAACP (UK), Dip. Osteopractic
Coordinator, American Academy of Manipulative Therapy Fellowship in Orthopaedic Manual Physical Therapy
Atlanta, GA

James Dunning, DPT, MSc (Manip Ther), MAACP (UK), FAAOMPT, Dip. Osteopractic
Director, American Academy of Manipulative Therapy Fellowship in Orthopaedic Manual Physical Therapy
Montgomery, AL

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