Tinnitus is the perception of a sound or noise in the absence of any actual external acoustic stimulus. This manifestation is considered a symptom and not a disease, as tinnitus is a sign of another underlying disorder. Today, 11.9% to 30.3% of adults suffer from tinnitus. However, only 0.5% to 3% of them feel that this disorder affects their quality of life.
Most people who suffer from tinnitus want to understand why the condition varies so much. For many patients, the perceived noise or sound changes from day to day or worsens at a specific time of day. Others experience symptoms after a nap. Some are fine when they wake up but hear increasingly louder sounds throughout the day.
Some patients even notice an increase in their tinnitus when they move their jaw, head, or body in a certain way. There are a great many triggers for tinnitus: increased salt intake in meals, stress levels, pathological factors, or environmental conditions are all elements responsible for short-term variations.
That said, a large proportion of affected individuals suffer from somatic tinnitus. Before delving into the details, let's take a moment to understand tinnitus in general.
Overview of Tinnitus
As we have just seen, tinnitus generally refers to the perception of a sound or ringing in the ears.
It often results from underlying problems: circulatory system disorder, hearing loss, or ear injury.
Even though it can impair quality of life or seriously interfere with daily activities, tinnitus is generally not life-threatening. The most common symptom is the perception of phantom sounds in the ears, such as:
Clicking
Buzzing
Hushing
Rumbling
Whistling
Roaring
These phantom sounds can be more or less loud and occur in one ear or both. In some cases, the sound is so intense that it prevents the patient from hearing external sounds or concentrating. Tinnitus can also be permanent or come and go.
There are two main types of tinnitus, one being much more common than the other: objective tinnitus and subjective tinnitus.
Subjective Tinnitus
Only the patient hears this type of tinnitus. This is the most common form, and it can have multiple origins:
Problems with the outer, middle, or inner ear.
Disorders of the auditory nerves.
Abnormalities of the auditory pathways, the area of your brain that interprets nerve signals as sounds.
Objective Tinnitus
A doctor can hear this type of tinnitus during the patient's examination, but it is extremely rare. Objective tinnitus can be caused by:
Conditions affecting the middle ear ossicles
Muscle contractions
Vascular problems
What is Somatic Tinnitus?
Somatic or somatosensory tinnitus (ST) is a subtype of subjective tinnitus caused by sensory information transmitted to the brain from the cervical spine or jaw.
Your somatosensory system is part of your sensory nervous system: it reacts to changes in your body, such as movement, pressure, temperature, and pain.
Like muscle spasms, somatic tinnitus can result from cervical (neck) or temporomandibular (jaw) changes.
It is also referred to as conductive tinnitus or cervicogenic tinnitus. "Conductive" simply means "caused by external functions." The term cervicogenic refers to an origin in the cervical spine or in the nerves and muscles of the neck.
Main Risk Factors for Somatic Tinnitus
The usual risk factors for other forms of tinnitus are hearing disorders, being male, and age. Patients with somatic tinnitus, however, present a different profile: they are most often young women with no known hearing problems.
The musculoskeletal disorders most frequently causing somatic tinnitus are cervical spine conditions and temporomandibular joint disorders. These patients also have a significantly higher prevalence of craniomandibular disorders.
This is easily explained, as somatic tinnitus is modulated by pressure exerted on the head, limbs, neck, or eye, by electrical stimulation of the median nerve, or by muscle contraction.
Studies also show that somatic modulation occurs in about two-thirds of tinnitus patients.
What is the Role of the Dorsal Cochlear Nucleus (DCN) in Somatic Tinnitus?
Your body transmits sensory information to your brain via nerve fibers located in the trigeminal ganglion or dorsal root ganglia. As these fibers project to the auditory system, the signals can trick the brain of patients with somatic tinnitus into believing it hears sounds.
The dorsal cochlear nucleus (DCN) is the first relay, or synapse, that auditory signals pass through before reaching the auditory cortex for processing. The DCN is located at the base of the brain, and "dorsal" refers to the back of your cochlear nucleus.
Your DCN is the most essential brainstem region for relaying auditory signals to the auditory cortex areas of your brain. It receives auditory signals from the cochlear hair cells responsible for detecting sounds, as well as signals related to eye movements.
The DCN also receives signals from muscle position sensors and transmits them to other brain regions. Acoustic data from your ears and sensory data from your muscles are thus sent simultaneously to the brain at the brainstem level.
This DCN can be damaged in many ways: head injuries, noise trauma, teeth grinding, whiplash, muscle spasm, or TMJ dysfunction can impair it.
Once the DCN is damaged, your neural structures shift into a state of hyperactivity that triggers interference between sensory and auditory signals. At this stage, sensory input influences auditory input and can cause, worsen, or modulate your tinnitus.
Even if the sounds seem to come from the ear, the nerve impulses are indeed generated in the DCN.
Given the DCN's important role, tinnitus is often considered a brain phenomenon. It persists even after the auditory nerve is severed, and deaf people can also suffer from it.
What Causes Somatic Tinnitus?
Specific triggers such as muscle spasms, dental problems, and TMJ disorders can cause somatic tinnitus.
Muscle Spasm in the Neck
A spasm is an involuntary contraction of the body's muscles, causing intense pain that can last from a few minutes to several days. Spasms occur in all parts of the body with muscles, including the neck.
One of the neck muscles most often affected by spasms is the sternocleidomastoid muscle (SCM). This muscle is located on each side of the neck, behind the ears, at the base of the skull.
The SCM runs down the front of the neck and attaches to the top of the collarbone and the sternum.
The sternocleidomastoid muscle is responsible for:
Lateral rotation of the head
Chewing and swallowing
Flexion of the neck forward to bring the chin to the chest
Assisting with breathing
