Tensor Tympani Syndrome

Etiology

Various etiologies have been associated with TTS and the broader category of middle ear myoclonus, including idiopathic causes, vascular abnormalities, demyelinating disorders, trauma, tumors, and infections. Many instances of bilateral TTS due to multiple sclerosis have been documented. However, the process of producing tinnitus has yet to be understood entirely. Tonic tensor tympani syndrome (TTTS) is described as causing tensor tympani spasms, which can lead to tinnitus and hyperacusis. An underlying anxiety disorder is believed to cause a reduction in the threshold required to trigger the tensor tympani muscle reflex, leading to the belief that TTTS is an involuntary condition.[4]

Epidemiology

Although studies regarding the epidemiology of TTS specifically are limited, a gender preference for middle ear myoclonus is not apparent. Additionally, early data regarding middle ear myoclonus suggest that it may occur more commonly in the third decade of life.[7]

Pathophysiology

The pathophysiology of TTS is not yet entirely understood. Researchers have proposed various etiologies with different pathophysiological processes. For example, a case of bilateral tensor tympani-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 from upper motor neurons. The contraction of the tensor tympani, described as a clicking sound, causes the tinnitus itself. The mechanism responsible for the perceived tinnitus may potentially lie with the muscle contraction itself, the vibration of the tympanic membrane, the opening and closing of the eustachian tube, a combination of these mechanisms, or an unknown factor.[8][9]

History and Physical

Clinicians should maintain a wide array of differential diagnoses in any patient presenting with tinnitus. While conducting a history and physical examination, the onset, laterality, duration, associated symptoms, and whether symptoms coincide with specific activities, eg, loud noises or changes in head position, should be noted. Frequently, the past medical history is unremarkable with no history of hypertension, endocrine diseases, recent medication changes, or any mental health history present. Among all the causes of tinnitus, even among the causes of objective tinnitus, tensor tympani myoclonus is rare. A thorough evaluation is therefore required to exclude more common and potentially more sinister etiologies of objective pulsatile tinnitus.[10][7]

CN V innervates the tensor tympani and tensor veli palatini (TVP) muscles. Due to the attachment of the tensor tympani muscle onto the malleus, during a spasm, the malleus is pulled anteromedially with inward movement of the tympanic membrane. Otoscopic findings have reported movement of the posterior quadrant of the tympanic membrane in stapedius myoclonus, contrasting with these conditions. However, these otoscopic findings are subjective, not specific, and still not widely accepted; they rely on a very experienced otoscopist's eye to discern. The TVP is activated to help elevate the palate during swallowing. Due to the dual innervation of the tensor tympani muscle by CN V, it can be activated and potentially cause tinnitus in some patients.

Additionally, CN V innervates the sensory component of the corneal reflex. As such, the corneal reflex can also activate the tensor tympani muscle, potentially causing TTS in some patients. Although the physical exam is unremarkable, unless the examiner is fortunate enough to view the spasmodically contracting eustachian tube orifice or tympanic membrane, some features can lead clinicians to suspect TTS. For example, during an otoscopic exam, rhythmic movements of the tympanic membrane have been observed at rest and even during blinking. In considering TTS as a diagnosis, clinicians should rule out palatal myoclonus by directly visualizing the palate and determining whether it coincides with reported tinnitus symptoms. A patulous Eustachian tube, accompanied by a complaint of autophony, must also be ruled out by tubotympano-aerodynamography. The most definitive way to diagnose middle ear myoclonus is through tympanotomy and direct visualization of the muscle spasm. However, this relies heavily on the chance that the patient is experiencing such an episode during examination. 

Evaluation

After a thorough history and physical examination, additional testing is available to rule out other potential etiologies. As TTS is rare, a definitive guideline for assessing this disorder is lacking, although an algorithm for diagnosis has been proposed. Audiometry is not typically used for diagnostic purposes, but it can potentially aid in masking treatment. However,  audiometry should be performed as this study is essential in ruling out other potential causes of tinnitus.

Tympanometry assesses the pressure of the middle ear at a given moment; however, if the tensor tympani is not contracting, tympanometry may not detect it. For this reason, long-term tympanometry can be used. Observing a sawtooth-like pattern representing tympanic membrane movement supports the diagnosis of TTS. An impedance audiogram is also helpful while diagnosing TTS by assessing the status of the middle ear. Static imaging modalities, such as magnetic resonance imaging (MRI) and computed tomography (CT), although not diagnostic of TTS, can also help exclude differential diagnoses of tinnitus.[11]

Treatment / Management

Management of patients with MEM, specifically TTS, varies depending on the severity of symptoms and each patient's expectations. As the etiology is not precisely understood, most treatments focus on anxiolysis and symptomatic management. Although no definitive guidelines or data regarding efficacy exist, medical and surgical approaches are available to alleviate symptoms.

Medical Therapies

Various medications, including benzodiazepines, carbamazepine, piracetam, botulinum toxin, and orphenadrine citrate, have been utilized for MEM with variable efficacy, each having different mechanisms of action.[4] 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 is also a muscle relaxant due to its anticholinergic and antihistamine properties. Piracetam is a gamma-aminobutyric acid derivative customarily used to treat cortical myoclonus. However, data on its use in MEM are lacking.[12] In epilepsy, primary hemifacial spasm, and trigeminal neuralgia, carbamazepine (a sodium-channel blocker) is a frequent treatment agent and has also found some success in TTS. Carbamazepine primarily operates by attenuating neuronal firing, resulting in decreased activity of its innervating muscles.(A1)

Another possible intervention that targets the contraction of the tensor tympani muscle is the botulinum toxin. Although new to MEM, botulinum toxin's well-documented use in noncosmetic otolaryngology-associated disease processes, such as hemifacial spasm, and laryngeal pathology (eg, spasmodic dysphonia), is notable. The mechanism of action of botulinum toxin is by preventing the release of acetylcholine from presynaptic neurons. Due to its limited use, researchers continue to examine the efficacy of botulinum toxin for MEM.

A case report has described the use of a botulinum-soaked absorbable gelatin-compressed sponge being applied intra-tympanically via a chronic tympanic membrane perforation. This 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 tensor tympani was unknown, so if a component of TTS is present, it cannot be determined whether the botulinum toxin affected both middle ear muscles.[4]

Surgical Intervention

The role of surgical intervention is more clearly defined. The most common procedure for TTS and stapedius myoclonus is tympanotomy with tensor tympani or stapedius tenotomy. Releasing the muscle's attachment site is believed to reduce or eliminate tinnitus. Researchers have described a limited number of case series evaluating the role of tenotomy in MEM. Bhimrao et al followed 13 patients who underwent stapedius tenotomy, 9 patients who underwent both stapedius and tensor tympani tenotomy, and a patient who underwent tensor tympani tendon sectioning. The decision to undergo a single tensor tympani tenotomy was due to direct visualization of isolated tensor tympani spasms.[12] All the patients in this series reported resolution except for one with associated palatal myoclonus.(A1)

Additionally, Park et al reported a case series of 44 patients initially treated with medical therapy. Approximately 75% of patients reported reduced symptoms, as indicated by visual analog scale and Tinnitus Handicap Index scores. Of the 11 patients who did not improve from medical therapy, 9 were elected for surgical intervention. Two patients in this group underwent bilateral tenotomy, and 7 patients underwent unilateral tenotomy. However, the distribution of the sectioned middle ear muscles is not specified. Surgical intervention does show promise in treating MEM. However, further studies are needed to clarify its role more precisely. Bhimrao et al advocate a 3-month trial of medical and supportive therapy before discussing tenotomy with possible tensor tympani or stapedius muscle sectioning.[13](A1)

Differential Diagnosis

Differential diagnoses that should be considered in patients presenting with tinnitus include:

• Stapedius myoclonus
• Palatal myoclonus
• Eustachian tube dysfunction
• Patulous eustachian tube
• Arteriovenous fistula or malformations
• Glomus tumors
• Carotid artery stenosis
• Aberrant vertebral artery
• Seizures
• Conversion disorder

Prognosis

Tinnitus itself is not physically harmful; however, it can cause a range of emotional distress in patients, from severely debilitating to causing little to no distress. While medical treatments have shown variable success, and anxiolysis is essential, surgical treatment of true TTS is very successful, with long-term cure rates of >90% routinely described.[14]

Complications

Complications of TTS primarily arise from its impact on a patient’s quality of life and the challenges associated with accurate diagnosis and management. Persistent, involuntary muscle contractions can lead to chronic discomfort, distressing auditory sensations, including clicking or fluttering, and heightened sound sensitivity (hyperacusis), which may interfere with daily activities, sleep, and mental health. Misdiagnosis or delayed recognition of TTS may result in unnecessary tests, inappropriate treatments, or failure to address coexisting conditions like anxiety, which can exacerbate symptoms. In rare cases, untreated or severe TTS may necessitate surgical intervention, which carries inherent risks associated with the procedure.