Tensor Tympani Syndrome

Etiology

There are various etiologies of TT syndrome and MEMs as a broader category, ranging from idiopathic, vascular, demyelinating disorders, traumatic, tumor, or infectious. There have been documented instances of bilateral TT syndrome due to multiple sclerosis. However, the process by which tinnitus is produced is not yet completely understood. Tonic tensor tympani syndrome (TTTS) has been described to cause TT spasms leading to tinnitus and hyperacusis. TTTS is believed to be an involuntary condition due to an overlying anxiety disorder, which causes a reduction in the threshold required to trigger the TT muscle reflex.

Epidemiology

Although there is limited information regarding the epidemiology of TT syndrome specifically, there does not appear to be a predilection of gender for MEM. Additionally, early data regarding MEM indicates that it can more commonly occur in the third decade of life.

Pathophysiology

The pathophysiology of TT syndrome is not completely understood; however, it can be caused by various etiologies with different pathophysiological processes. For example, a case of bilateral TT-induced tinnitus in a patient with multiple sclerosis was suspected to be due to the demyelination of innervating nerves, leading to muscle spasms. Alternatively, the myoclonic activity may be due to medullary activity centers no longer receiving inhibitory signals by upper motor neurons. The tinnitus itself is caused by the contraction of the TT, which has been described as a clicking sound. It is possible that the muscle contraction itself, the vibration of the tympanic membrane, the opening and closing of the Eustachian tube, a combination of these mechanisms, or a different unknown mechanism is responsible for the perceived tinnitus.[8][9]

History and Physical

It is crucial to keep a wide differential with any patient who presents with a complaint of tinnitus. While conducting a thorough history and physical, it is important to note the onset, laterality, duration, associated symptoms, and whether symptoms coincide with certain activities. CNV innervates the TT and tensor veli palatini (TVP) muscles. Due to the attachment of the TT muscle onto the malleus, during a spasm, the malleus is pulled anteromedially with inward movement of the tympanic membrane. This can be contrasted to otoscopic findings for stapedius myoclonus, in which movement of the posterior quadrant of the tympanic membrane has been reported. However, these otoscopic findings are subjective, not specific, and still not widely accepted. During swallowing, the TVP is activated to assist in elevating the palate. Due to this dual innervation by CNV, the TT muscle can be activated and possibly cause tinnitus in some patients. Additionally, CNV innervates the sensory component of the corneal reflex. As such, the corneal reflex can also activate the TT muscle, which can cause TT syndrome in some patients. Although the physical exam is largely unremarkable, some features can lead clinicians to suspect TT syndrome. For example, while conducting an otoscopic exam, rhythmic movements of the tympanic membrane have been described at rest and even during blinking. Additionally, while considering TT syndrome as a diagnosis, palatal myoclonus must be ruled out by direct visualization of the palate and whether it coincides with reported tinnitus symptoms. Patulous Eustachian tube with a common primary complaint of autophony must also be ruled out by tubo-tympano-aerodynamography. The more definitive way of diagnosing any MEM is by tympanotomy and direct visualization of the muscle spasm. MEM is characterized as objective tinnitus, so auscultation of the ear can be helpful during a physical exam.

Evaluation

After a thorough history and physical, additional testing is available to rule out other etiologies. As TT syndrome is a rare finding, there is no definitive guideline to assess for this disorder, although an algorithm for diagnosis has been proposed. Audiometry is not typically used for diagnostic purposes but can potentially aid in masking treatment. Tympanometry will assess the pressure of the middle ear at a given moment, but if the TT is not contracting, it may not be observed by tympanometry. For this reason, long-term tympanometry can be used. A saw-tooth-like pattern representing tympanic membrane movement can be seen, which supports the diagnosis of TT syndrome. An impedance audiogram is also helpful while diagnosing TT syndrome by assessing the status of the middle ear. Imaging such as CT and/or MRI can also be helpful to rule out other potential causes of tinnitus.

Treatment / Management

Management of patients with MEM, as well as specifically TT syndrome, varies depending on the patient’s severity of symptoms and expectations. If the patient is interested in treatment, there are various approaches to decreasing symptoms. Again, although there are no definitive guidelines as well as no definitive data regarding efficacy, there are medical and surgical approaches to decreasing symptoms. Several medications have been reportedly used for MEM with questionable efficacy, including benzodiazepines, carbamazepine, piracetam, botulinum toxin, as well as orphenadrine citrate with varying mechanisms of action. Benzodiazepines can be used to potentially decrease symptoms by targeting the anxiolytic component of the disorder as well as functioning as a muscle relaxant. Orphenadrine citrate also acts as a muscle relaxant due to its anticholinergic and antihistamine properties. Piracetam is a GABA derivative normally used to treat cortical myoclonus; however, there is extremely limited data on its use in MEM. Carbamazepine, a sodium-channel blocker, attenuates neuronal firing leading to decreased activity of their innervating muscles, which is why it is primarily used in epilepsy, primary hemifacial spasm, and trigeminal neuralgia. Another possible intervention that targets the contraction of the TT muscle is via botulinum toxin. Although the use of botulinum toxin is new to MEM, its use in non-cosmetic otolaryngology-associated disease processes like hemifacial spasm as well as laryngeal pathology such as spasmodic dysphonia is well documented. The mechanism of action of botulinum toxin is by preventing the release of acetylcholine from pre-synaptic neurons. The efficacy of botulinum toxin for MEM is still being examined due to its limited use. There has been a case report describing the use of botulinum soaked absorbable gelatin compressed sponge being applied intratympanically via a chronic tympanic membrane perforation. This particular patient was diagnosed with stapedius myoclonus by direct visualization of stapedius spasm. The patient experienced symptomatic relief for approximately 3 months, however similar to other disease processes treated with botulinum toxin, its effects were time-limited. The status of the TT was unknown, so if there was a component of TT myoclonus as well, it could not be determined if the botulinum toxin affected both middle ear muscles.

The role of surgical intervention is also more clearly defined. The most common procedure for TT syndrome as well as stapedius myoclonus is tympanotomy with TT or stapedius tenotomy. It is believed that by releasing the muscle's attachment site, it can reduce or eliminate tinnitus. A limited number of case series evaluating the role of tenotomy in MEM has been described. Bhimrao et al. reference 13 patients who underwent stapedius tenotomy, nine patients who underwent both stapedius and TT tenotomy, and one patient who underwent TT tendon sectioning. The decision to undergo single TT tenotomy was due to direct visualization of isolated TT spasms.[10] All the patients in this series reported resolution except for one who had associated palatal myoclonus. Additionally, Park et al. reported a case series of 44 patients who were initially treated with medical therapy. Seventy-five percent of patients reported a decrease in symptoms based on visual analog scales and tinnitus handicap index scores. Of the eleven patients who did not improve from medical therapy, nine of them elected for surgical intervention. Two patients in this group underwent bilateral tenotomy, and seven patients underwent unilateral tenotomy. However, the distribution of the middle ear muscles sectioned is not specified. Surgical intervention does show promise to treat MEM. However, more studies should be conducted to more clearly define its role. Bhimrao et al. advocate a 3-month trial of medical and/or supportive therapy before discussing tenotomy with possible TT or stapedius muscle sectioning.(A1)

Differential Diagnosis

When evaluating a patient with a complaint of tinnitus, the history and physical will help refine the differential diagnosis. All causes of objective tinnitus should be considered when developing a differential diagnosis. Stapedius myoclonus and palatal myoclonus are very high on the differential in a patient with TT syndrome as all three can present similarly. History, physical, as well as tympanometry can direct a clinician to one or more potential diagnoses, but the most definitive diagnosis is by direct visualization of TT spasm. Other conditions to be considered are a patulous Eustachian tube, arteriovenous fistula or malformations, glomus tumors, carotid artery stenosis, and other atherosclerotic diseases. However, these other disorders will most likely present with different history and physical exams as well as more definitively distinguished by audiometry and imaging.

Prognosis

Tinnitus is not harmful; however, depending on the etiology, the underlying process can be life-threatening, such as multiple sclerosis. Other than the underlying disease process, tinnitus can cause a range of emotional distress to patients, from severely debilitating to causing little to no distress to the patient. Additionally, there is not enough data at this time to predict whether symptoms will discontinue or reduce, regardless of whether there is an identifiable cause for the tinnitus or idiopathic in origin.