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OBJECTIVE TINNITUS and the TENSOR TYMPANI MUSCLE Erwin H

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OBJECTIVE TINNITUS and the TENSOR TYMPANI MUSCLE Erwin H 30 International Tinnitus Journal Vol. I, No.1, 1995 OBJECTIVE TINNITUS AND THE TENSOR TYMPANI MUSCLE Erwin H. Rock, M.D., F.A.C.S. ABSTRACT processus cochleariformis (also called trochlear­ iformis) and attaches to the medial aspect of the Objective tinnitus (OT) may be caused by root of the manubrium. The TTM is supplied contraction of the tensor tympani muscle by a motor branch coming from the mandibular (TTM). The more forcefully the TTM contracts, division of cranial nerve (CN V). This branch, the greater the intensity of the OT heard. before passing through the otic ganglion Forceful closure of both eyelids can reflexively without synapsing, sends a branch to the me­ cause OT by contracting the TTM. The Forceful dial pterygoid muscle and finally innervates the Eyelid Closure Syndrome (FECS) was reported at TTM.2 The name of the muscle is derived the Proceedings of the Second International from the fact that it draws the handle of the Tinnitus Seminar in 1983.1 malleus medially and forward and thus FECS consists of several factors: consequently tenses the TM. The contracting (1) Objective tinnitus TTM also pushes the stapes more tightly into (2) An associated waning of hearing primarily the oval window. of the lower frequencies, as much as 45 dB at The stapedius muscle, the smallest 125 Hz, 30 to 40 dB at 250 Hz ascending to the skeletal muscle in the body, originates from a patient's norm at 2000 Hz and approximately a conical cavity in the pyramidal eminence and 5 to 10 dB at 4000 Hz and 5 to 20 dB at 8000 Hz its tendon passes through an opening at the (3) Retraction of the manubrium and posterior apex of this eminence to insert on the neck of mid-third of the tympanic membrane (TM) at the the stapes. It is supplied by motor CN-VII. The malleus-umbo area as seen under the otomicro­ muscle pulls the stapes posteriorly and tilts the scope (OM) in 25% (108) of 432 ears examined posterior segment of the footplate into the oval (4) These same ears were 75% (324) positive for window while the anterior part of the footplate increased impedance at maximum compliance is pulled outwardly. This action tightens the with FEe. Of the patients studied, 25% had no annular ligament and thus dampens the stapes' response under the otomicroscope or by vibratory capacity below 2000 Hz.2 impedance audiometry. Stiffness is increased when both middle­ ear muscles contract together more than with a singular response. The contraction of the two ANATOMY AND MYOKINESIS muscles is synergistic but not truly additive. The contracting stapedial muscle initially The length of the TTM is between 20 to displaces the TM laterally and is minimally 25 mm or approximately four times longer than antagonistic to the medial retraction of the TM the stapedius muscle. Both of these bipenniform by the action of the TTM. Suffice to say each middle-ear muscles increase impedance of the contracting muscle increases the acoustic middle-ear mechanism to a sound wave by impedance of the sound wave.3 stiffening the TM, the ossicular chain, and its FEC can initiate a reflex that causes ligaments. The bipenniform anatomy creates a contraction of the TTM. The normal eye blink forceful muscular contraction with minimal rarely displays the forceful eyelid closure reflex displacement. (FECR). The reflex sequence is motor CN-VII TTM arises from the cartilaginous part activating the orbicularis oculi muscles relaying of the eustachian tube and an adjacent part of to motor CN-V to the TTM. A loud sound can the greater wing of the sphenoid bone and also elicit the well-known cochleo-palpebral reflex, from its own bony semicanal. It is housed affecting sensory CN-VIII to motor CN-VII. If within this bony semicanal above the bony part the eyelid closure is forceful enough, the reflex of the eustachian tube and terminates into a thin can go on to cause TTM contraction. This is tendon, which turns laterally around the especially true if the initial sound created a Objective Tinnitus and the Tensor Tympani Muscle 31 startle effect. When the FECS is active, the for increased impedance in 75%. Increased manubrium and the mid-third of pars tens a of impedance causes a hearing loss for as much the TM posterior to the malleus-umbo area as 45 dB at 125 Hz, 30 to 40 dB at 250 Hz and toward the middle ear retract. The greater the ascending to patient's norm at 2000 Hz and force of the orbicularis oculi muscle contraction, approximately a 5 to 10 dB at 4000 Hz and 5 to the greater will be the degree of area circum­ 20 dB at 8000 Hz (Fig. 1). Impedance audio­ ference and intensity of TM retraction. Repeated metry is carried out at maximal compliance. forceful eyelid contractions eventually habit­ American Electromedics' AE 83 and the AE 803 uate the reflex. It may take seconds to several impedance audiometers were used in this study. minutes of orbicularis oculi muscle relaxation In humans the TTM is not activated by sound before this reflex recurs. per se as the stapedius muscle is. In other Impedance audiometry is three times animals, however, both the TTM and stapedius more sensitive than observing the TM dynamics muscle respond to acoustic stimuli.3-6 under the OM, at 10 power. Initially, 432 ears were examined routinely under the OM to note HISTORIC the presence or absence of FECR. All ears had an intact TM without tympanosclerosis. The TM retraction was positive in 25% of these ears Hitzig,7 Lucae,8 and Tschiassny9 in 1869, whereas impedance audiometry was positive 1874, and 1946, respectively, described a ERWIN H. ROCK, M.D., F.A.C.S. AUDIOGRAM 970 North Broadway, Yonkers, N.Y. Y NAME O. w. AGE 38 DATE 5/3/83 No. TI.IIPANOG~.~II RT LT U.S 250 500 1000 2000 4000 1000Hz Curvi 10 ~Ul'!~L-_ 1-- 1---- ISO IIEP 0 -0011\ ~ ANSI I::.ONTRA. ACOUSTIC REFLEX (AR) .JI\,. 0 LT 1"/ ~ I>~~ ~~ ~ AU 0 Probe RT &;. !:I~ - THRESH.dB -.....l1lI 250 + + 20 r-- ~ 500 + + 10... ') ~ RT.A.C. 0 1000 + + I:: 30 /" IIUD' 2000 + + <.; LEFT A.C . AR DECAY X I!l 40 . ~ l' '.LUE' PIIoM RT LT Hz dB j 50 i" 500 NoRell. NoRell. ~ RT. B.C. 1000 NoRell. NoRell. z '''ED' > "i 60 500 110 DecI, NoOecl, c LEFT B.C. 1000 110 Decl' No 0 ..1, ~ A PUR ~ TONE ~ HRESHOLP '.LUE' < 500 Dec. S. Dec. Sec 70 1000 Dec. Se Dec. Sec FOR "ED EYEl ID CLOS RT L T 80 ~ iPSI REFLEX • PB Hz THRESH.'B RT LT 250 + + 90 SRT 500I_ + . · 100 2_ + · - Fig. 1. Audiogram of patient O.W. with an active forceful eyelid closure reflex 32 International Tinnitus Journal Vol. I, No.1, 1995 FREQUENCIES IN CYCLES PER SECOND 12~ Z~O 500 1000 2000 4000 8000 -30 -30 -20 -20 -10 -10 D-- __ --~ [)..---- 0 0' , o CI) (IY--- ~'O',.I -' / ~ ~,- w 10 &a 10 .----w '»:-"~ •c::; 20 V 20 w 0 30 / 30 z ./ ;;; 40 I"" 40 ~ ~O ~O ..J C)z 60 60 ~ 70 70 wc ~ 80 80 Fig. 2. 0---------0 average threshold sensitivity of both ears with middle ear muscles relaxed ~--~ average sensitivity of both ears during maximum voluntary contraction of middle ear muscles (one subject, after Smith) Fig. 3. Appearance of the membrane tympany during contraction of the tensor tympani muscle (after Smith, 1943) Objective Tinnitus and the Tensor Tympani Muscle 33 blowing sound heard deep within the ear Salomon and Starr (1963)16 studied the simultaneous with voluntary contraction of the electromyography (EMG) of the middle ear periorbital muscles. They attributed this to muscle activity of the TTM and stapedius stapedius muscle contraction. Forced eye muscle on two patients. One patient was closure (FEC) and changes in impedance have observed before labyrinthectomy and the been observed by Geffcken,5 Klockhoff6 and second through a TM perforation. They found Moller.3 Geffcken, however, in 1934, felt that the that the TTM responded for up to 15 milli­ change in impedance secondary to FEC was seconds before eye closure and increased both caused by the TTM.5 frequency and amplitude of TTM potentials. Voluntary contraction of the TTM was With relaxed eye closure, no tensor tympani recognized by Luschka and Politzer over 100 activity was found. TTM activity occurred 20 years ago. Politzer (1909)11 reported the to 60 milliseconds after periorbital activity using following about a patient, "during the con­ an air jet blown against the eyes. Voluntary FEC tractions the hearing distance was diminished created a more consistent tensor activity than and deep tones became deadened and indistinct that caused reflexively by the orbital air jet. and the high tones ascended one quarter of a Habituation occurred rapidly. Jaw muscle tone." activity did not activate the TTM. Smith (1943), a captain in the United TTM activity was always elicited before States' Army Medical Corps, reported on the or simultaneously with talking or humming. audiometric findings of a lieutenant who could Therefore this represents a non-acoustic voluntarily contract his TTM.12 At 8 to 9 years function because of the loss of the normal of age he became aware that he could produce skeletal muscular latency period. Forceful a low-pitched roar in both ears when he voluntary eyelid closure or orbital air jet activity voluntarily contracted the muscles, and was not associated with any changes of simultaneously diminished hearing enough to stapedius muscle activity. block out ordinary conversation (Fig. 2). Visual observation using an OM demon­ Boring conversations could be blocked strated stapedius muscle activity during out at will by voluntary contraction of the TTM.
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