Tensor Tympani and Stapedius Myoclonus Tinnitus

Timothy C. Hain, MD . •Page last modified: September 23, 2019

Inspection of the eardrum may sometimes demonstrate subtle movements due to contraction of the tensor tympani (Cohen and Perez, 2003). As Schwartze first described in 1864, tensor tympani myoclonus causes a thumping sound.

Anatomy of the tensor tympani and stapedius

Stapedius and Tensor Tympani Muscles Cartoon of the middle ear showing muscles that attach to ossicles (ear bones), and ear drum. The stapedius is attached to the stapes (of course -- horseshoe object above), while the tensor tympani is attached to the ear drum. While useful, be aware that there are multiple errors in this illustration from Loyola Medical School. With permission, from: https://www.meddean.luc.edu/lumen/meded/grossanatomy/dissector/mml/images/stap.jpg

The tensor tympani and stapedius muscles are shown above. The tensor tympani is contiguous with a palatal muscle, the tensor veli palatini. Thus contractions of the tensor tympani may also be accompanied by contraction of the palatal muscles. Both the TT an TVP are innervated by the 5th nerve. Hieronymus Fabricius, an Italian (1533-1619) was the first to propose theories on tensor tympani function. He suggested that there was both a protective and non auditory role to the tensor tympani. Both the stapedius and tensor tympani are striated muscles. The stapedius is about 6mm in length, arises from the pyramidal process and the tendon attaches to the posterior neck of the stapes. The stapedius is a muscle with a high oxidative capacity. It is innervated by the stapedial branch of the facial nerve (7th nerve). The tensor tympani is about 25 mm in length. The muscle is not as strong as the stapedius, and the tendon also contains more elastic tissue and fat. The tensor tympani courses through a bony canal in the wall of the anterior middle ear, and attaches to the neck of the manubrium. A bony partition separates the tensor tympani from the eustachian tube. The tensor tympani is innervated by a branch of the mandibular division of Cranial Nerve V, via the otic ganglion. While the nerve passes through the ganglion, it does not synapse there. (Mukerji et al. 2010)

What do these muscles do ?

Stapedius and Tensor Tympani Muscles Image showing middle ear and tensor tympani from Gray's anatomy https://upload.wikimedia.org/wikipedia/commons/2/24/Musculustensortympani.png

The tensor tympani and stapedius muscles are protective reflexes. They reduce the amount of sound that gets into the inner ear. They are somewhat similar to the blink reflex. Thus they can be triggered by loud noise, and when they "go off", both ears can be involved. This is similar to the situation that occurs when one eye is irritated, and both eyes blink for hours. Again like blinks, these protective reflexes can become more prominent when a person is under stress. The stapedius is more sensitive to sound than the tensor tympani, and is thought to be the "dominant sound generated reflex in humans). It's two roles are thought to be reduction of sound through modulation of middle ear impedance, and prevention of masking of speech through high-pass filtering of low frequency sound (background noise). The stapedius may also contract to internal vocalization to reduce self-stimulation. Regarding the tensor tympani, there is "minimal electrical activity" to sound presented to both ears, and there is no acoustic reflex in persons who have 7th nerve palsies (paralyzing the stapedius). On the other hand, the tensor tympani may be activated by: Tactile stimulation of EAC and face (Klockhoff, 1961; Klockhoff and Anderson, 1959)

Pneumatic pressure on eyelids (Klockhoff and Anderson, 1960),

Sudden forced opening of closed eyelids (Terkildsen, 1960), or forced closing of eyelids (Kaffenberger et al, 2016).

Swallowing (Wersall, 1958)

Head movements (Carmel and Starr, 1963)

Anticipation of loud sounds (Borg et al, 1984)

Startle. (Borg et al, 1984)

Disorders of the tensor tympani

The tensor tympani syndrome is uncommon. The only known epidemiological study regarding it was from the Mayo clinic, where incidence was estimated as 1.3 cases/100,000 person years (Caviness et al, 1999) It sometimes results in visible contractions of the ear drum, and sometimes even produces sounds audible to the examiner. Patients usually indicate that it makes a "thumping" noise -- like a tympani drum ! There have also been occasional reports of higher frequency sounds (Bento et al, 1998; Abdul-Baqi, 2004). A strange variant of the tensor tympani is the so-called "forced eyelid closure syndrome". Kaffenberger et al (2016), discussed treatment of this poorly named "syndrome", really just another trigger for tensor tympani myoclonus, with botulinum toxin in the palate, presumably to paralyze the tensor tympani. Klockhoff suggested that the "tensor tympani syndrome" may be caused by increased psychic tension and psychosomatic muscle dysfunctions in the scalp and middle ear. The formulation seems somewhat similar to blinking -- people blink more when they are under stress. Stapedius myoclonus has been reported once in "benign fasciculation syndrome" (Brigo et al, 2013), basically a diagnosis where patients become "twitchy" without an identified cause. This information is not especially useful, but it does suggest the general idea that when muscles are more irritable, tinnitus can result. We have had a single interesting case where a patient with TTM had a very large hair growing out of the side of her ear canal and brushing up against the ear drum. When this hair was snipped, her TT went away ! If only it was always so easy. Presumably the mechanism her was irritation of the ear drum.

Diagnosing TT myoclonus.

There are several simple methods of diagnosing TT myoclonus. The easiest is to simply watch the ear drum with an otoscope. When the muscle contracts, the eardrum dimples. A second easy method is to listen. One can often hear the tinnitus by putting one's ear next to the patients ear. It generally is not useful to use a stethoscope. An impedance bridge (tympanometer) can document rhythmic changes in ear drum compliance. A long recording of ear drum compliance should be made with a tympanometer (a screener won't work here). According to Bance, tensor tympani function can be measured by detecting changes in middle ear impedance. They also noted that the most effective method of stimulating it are orbital puffs of air --i.e. the same as the stimuli that might elicit a blink ( Bance et al, 2012). Audiology research project ideas: one might be able to measure "thresholds" for the air puff stimulus, or loud noises, or chewing/gritting the teeth/forceful eye closure -- using similar methodology to blink reflexes, and thus develop a better method of diagnosing TT myoclonus.

Another middle ear tinnitus - -stapedius myoclonus syndrome.

There should not be movement of the ear drum in the stapedius myoclonus syndrome, as the stapedius does not insert onto the eardrum but rather onto the stapes. The stapedius is innervated by the 7th nerve, and is therefore part of a different circuit than the tensor tympani (5th nerve). In our experience (see recording below), the sound can be heard from the outside -- it is a high-pitched "tic". We were unable to hear with a stethoscope. however, possibly due to it's high pitch. There was no visible movement of the eardrum.

Rhythmic changes in impedance of the middle ear. Each bump was correlated with a high-pitched "tic" that can be heard from the outside, due to stapedius myoclonus.

Click below to play recording of stapedius myoclonus.

Your browser does not support the audio element.

A similar clinical picture may be associated with "typewriter tinnitus" as described by Levine (2006). Levine attributed this type of tinnitus to irritability of the 8th nerve. This tinnitus is intermittent and has a staccato quality ('like a typewriter in the background, pop corn, Morse code'). It is responsive to carbamazepine. In our view, this clinical picture would be difficult to distinguish from stapedius myoclonus without careful clinical examination. TT myoclonus should be associated with a visible displacement of the ear drum during the sound. Stapedius myoclonus should be audible to the examiner, also one should be able to record it from an external ear microphone and it should be higher pitched. We do not know of anyone who has reported this however.

Treatment of TT myoclonus that may work.

Surgery to cut the muscle is effective, and is used as a last resort. According to Bhimrau et al (2012), the facial nerve is often damaged during this sort of surgery. However, it is generally successful in stopping the myoclonus. A recent report suggested using Botox to paralyze the muscles (Liu et al, 2011). Botox can be injected into the wall of the eustachian tube. Of course, the TT is a small muscle and thus only a small amount of Botox is needed (Botox, sold by Allergan, is extremely expensive). This treatment seems reasonable, except that one needs an individual to administer the Botox who has a very good understanding of the anatomy of the TT to administer the injection, and also Botox wears off in 3 months. Treatment of these muscle spasm syndromes is usually reassurance. Tinnitus coping strategies of counselling, relaxation and anxiety reduction are standard practice. Hypnosis, sedatives, psychotherapy, acupuncture, biofeedback have been attempted -- as this type of tinnitus is somewhat related to stress, these strategies are sometimes helpful.

Treatments of TT myoclonus that probably don't work.

Medications responses were reported by Bhimrau et al (2012)

Benzodiazepines (too much sedation)

orphenadrine (Norflex)

carbamazepine

piracetam (one patient)

botulinum toxin (one patient, gelfoam in middle ear)

As can be seen, very little treatment has been reported. While the logic of reducing muscle spasm through medication is reasonable, we ourselves have not had success. It seems to us that the TT muscle requires considerable local irritation to develop myoclonus, and medications that affect the whole body are unable to reduce such intense local spasms.

Although masking has been reported effective (East et al, 1987), it is difficult to see a reasonable rationale, and we suspect this is a placebo.

Pharyngeal muscle tone alteration, swallowing, Valsalva, and grommet insertion are not effective (Badia et al, 1994).

We are similarly dubious that manual compression of the face as reported by Chan and Palaniappan (2010) has any general utility as it would seem to us that any relief would be necessarily brief.

Treatments of TT myoclonus that we wish someone would develop

What is needed is a method of selectively weakening these muscles through drops administered through a ventilation tube or grommet. Alternatively, a method of causing a longer paralysis of the TT than can be obtained using Botox. Attacking the reflex at the neural level would also seem possible -- perhaps a method of cutting the nerve to the TT muscle.

References: