Tensor Tympani Syndrome

Etiology

TTS causes spasms of the tensor tympani muscle, potentially resulting in tinnitus and hyperacusis. TTS may account for the aural pain and tinnitus often associated with hyperacusis, which can be triggered by exposure to loud noises that elicit a startle reflex. Various factors have been linked to TTS and the broader category of middle ear myoclonus, including idiopathic origins, vascular issues (eg, arteriovenous fistula or malformations, atherosclerosis, and carotid artery stenosis), demyelinating conditions, trauma, tumors (eg, glomus), and infections. TTS may be a secondary consequence of temporal mandibular joint dysfunction.[4]

Numerous cases of bilateral TTS attributed to multiple sclerosis have been reported. Nevertheless, the mechanism behind tinnitus development remains incompletely understood. An underlying anxiety disorder is believed to lower the threshold needed to activate the tensor tympani muscle reflex, supporting the hypothesis that TTS is an involuntary condition.[8]

Epidemiology

The sole epidemiological study on middle ear myoclonus in a specific area estimated a lifetime prevalence of 8.6 cases per 100,000 population as of 1990. The authors acknowledged that myoclonus is not recognized by the patient or their family and does not constitute a clinical diagnosis.[23] While research on the epidemiology of TTS is scarce, no evident gender preference has been noted for middle ear myoclonus. Furthermore, initial data indicate that middle ear myoclonus may be more prevalent during the third decade of life.[11]

Pathophysiology

The pathophysiology of TTS remains largely unclear. Various etiologies have been suggested, each involving different pathophysiological mechanisms. For instance, in a case of bilateral tensor tympani-induced tinnitus in a patient with multiple sclerosis, demyelination of the innervating nerves was suspected to cause muscle spasms. Alternatively, the myoclonic activity might originate from medullary activity centers that no longer receive inhibitory signals from upper motor neurons. The contraction of the tensor tympani, which is perceived as a clicking sound, triggers the tinnitus. The underlying mechanism for the perceived tinnitus may involve the muscle contraction itself, tympanic membrane vibration, eustachian tube opening and closing, a combination of these factors, or an unknown cause factor.[24][25]

History and Physical

Clinical History

Clinicians should consider a wide array of differential diagnoses for patients with tinnitus. Accurate characterization of the patient's symptoms when obtaining the clinical history, including the onset, laterality, duration, associated symptoms, and potential triggers (eg, exposure to loud noises or changes in head position) is crucial. Often, no significant findings are apparent in the patient's medical history, including signs of hypertension, endocrine disorders, recent medication changes, or documented mental health problems. Among the numerous causes of tinnitus, tensor tympani myoclonus is rare, especially for objective tinnitus; therefore, a thorough assessment is needed to eliminate more common or potentially serious causes of objective pulsatile tinnitus.[26][11]

Additionally, differentiating between pulsatile and nonpulsatile tinnitus is crucial. Pulsatile tinnitus is associated with vascular conditions, eg, a high-riding jugular bulb or atherosclerosis, and usually aligns with the heartbeat. Conversely, nonpulsatile tinnitus may result from issues including sensorineural hearing loss or otosclerosis, which patients may describe as fluttering, flapping, or clicking, and does not match the heartbeat.

TTS, or tensor tympani myoclonus, is a rare condition marked by spasmodic contractions of the tensor tympani muscle, resulting in "objective" tinnitus that others can hear when auscultating the affected ear during a myoclonus episode. Pulsatile tinnitus describes the perception of rhythmic sounds coinciding with the heartbeat, which is quite common and should be differentiated from TTS. The tensor tympani muscle is essential in various auditory functions, including controlling the eustachian tube movement and stiffening the tympanic membrane to moderate sound transmission during loud noises.

Physical Examination

CN V innervates the tensor tympani and tensor veli palatini muscles. When the tensor tympani muscle spasms, it pulls the malleus anteromedially, leading to the inward movement of the tympanic membrane. Otoscopic examinations have shown movement in the posterior quadrant of the tympanic membrane in stapedius myoclonus, highlighting the difference. However, these findings are subjective and not widely accepted; their interpretation requires skills from a highly experienced otoscopist. The tensor veli palatini aids in elevating the palate during swallowing. Given CN V's dual innervation of the tensor tympani muscle, its activation might lead to tinnitus in some patients.

Moreover, CN V also relates to the sensory aspect of the corneal reflex. This connection can cause the tensor tympani muscle to activate, potentially resulting in TTS in specific individuals. Despite a routine physical examination, certain signs may prompt clinicians to consider TTS, unless the perceptive examiner happens to observe the spasmodically contracting eustachian tube or tympanic membrane. For instance, rhythmic movements of the tympanic membrane can be seen during otoscopic exams, even at rest or while blinking. When evaluating TTS as a diagnosis, clinicians should exclude palatal myoclonus by visually inspecting the palate and checking its relation to the reported tinnitus symptoms. Additionally, a patulous eustachian tube alongside complaints of autophony should be assessed using tubotympano-aerodynamography. The most conclusive method for diagnosing middle ear myoclonus involves tympanotomy and direct observation of the muscle spasm, which heavily depends on the patient's chance of having an episode during the examination. 

Evaluation

Further testing should be performed to exclude other possible causes after a thorough clinical examination. Since TTS is uncommon, no definitive guideline for evaluating this disorder has been established; however, a diagnostic algorithm has been proposed. While audiometry is not generally used for diagnostic purposes, this study is crucial as this examination helps rule out other potential causes of tinnitus.

Tympanometry measures middle ear pressure at a specific moment; however, it may fail to detect when the tensor tympani is not contracting. Consequently, implementing long-term tympanometry can be beneficial. Detecting a sawtooth-like pattern indicative of tympanic membrane movement supports a TTS diagnosis, but may not be definitive for diagnosis. An impedance audiogram is also helpful in diagnosing TTS by evaluating middle ear status. Although not diagnostic for TTS, static imaging techniques, eg, magnetic resonance imaging (MRI) and computed tomography (CT), can help exclude other differential diagnoses of tinnitus.[27]

Treatment / Management

The management of patients with middle ear myoclonus, particularly TTS, depends on symptom severity and individual patient expectations. Since the exact cause is not fully understood, most treatments aim to provide anxiolysis and manage symptoms. While no conclusive guidelines or efficacy data exist, medical and surgical options are available to help reduce symptoms.

Medical Therapies

A range of medications, including benzodiazepines, carbamazepine, piracetam, botulinum toxin, and orphenadrine citrate, have been employed for middle ear myoclonus, exhibiting varying levels of efficacy, with distinct mechanisms of action.[8] Benzodiazepines may help reduce symptoms by addressing the disorder's anxiolytic component and acting as muscle relaxants. Orphenadrine citrate is also a muscle relaxant because of its anticholinergic and antihistamine properties. Additionally, piracetam, a derivative of gamma-aminobutyric acid, is commonly prescribed for cortical myoclonus. However, the data on its use in middle ear myoclonus is limited.[28] Carbamazepine, a sodium-channel blocker, is widely used to treat epilepsy, primary hemifacial spasm, and trigeminal neuralgia, and has also shown some effectiveness in treating TTS. Carbamazepine primarily reduces neuronal firing, leading to decreased activity in the muscles it innervates.(A1)

Another potential intervention for targeting the contraction of the tensor tympani muscle is botulinum toxin. While relatively new to the management of middle ear myoclonus, the extensive application of botulinum toxin in otolaryngology for noncosmetic conditions (eg,  hemifacial spasm) and laryngeal disorders (eg, spasmodic dysphonia) is significant. Botulinum toxin works by blocking the release of acetylcholine from presynaptic neurons. Given its limited use in this context, researchers are actively investigating the effectiveness of botulinum toxin for middle ear myoclonus.

One case report detailed using a botulinum-soaked absorbable gelatin-compressed sponge applied intra-tympanically through a chronic tympanic membrane perforation. The patient, diagnosed with stapedius myoclonus via direct observation of stapedius spasm, reported symptom relief for about 3 months. Nevertheless, similar to other conditions treated with botulinum toxin, these effects were temporary. The condition of the tensor tympani remained uncertain, making it impossible to ascertain whether the botulinum toxin influenced the middle ear and any potential contribution of the TTS muscles.[8]

Surgical Intervention

The standard surgical treatment of TTS is primarily tympanotomy accompanied by tensor tympani or stapedius tenotomy. This surgical approach aims to release the muscle's attachment, potentially reducing or eliminating tinnitus. Researchers have identified only a few case series assessing the impact of tenotomy in middle ear myoclonus. Bhimrao et al studied 13 patients with stapedius tenotomy, 9 receiving stapedius and tensor tympani tenotomy, and 1 with tensor tympani tendon sectioning. The choice to perform a solitary tensor tympani tenotomy was based on the direct visualization of the isolated tensor tympani spasms.[28] Every patient in this series reported resolution, except for a case with palatal myoclonus.(A1)

Furthermore, Park et al reported on a case series involving 44 patients initially treated with medical therapy. About 75% of these patients showed symptom reduction, as measured by visual analog scale and Tinnitus Handicap Index scores. A reported 9 of the 11 patients who did not experience improvement with medical therapy opted for surgical intervention. Within this group, 2 patients underwent bilateral tenotomy, and 7 received unilateral tenotomy. However, the study did not provide specifics regarding the division of the severed middle ear muscles. Subsequently, surgical intervention appears promising for treating middle ear myoclonus, yet more research is necessary to define its role. Bhimrao et al recommend a 3-month trial of medical and supportive therapy before contemplating tenotomy involving the tensor tympani or stapedius muscle sectioning.[29][3](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 is not physically damaging, but it can lead to a spectrum of emotional distress, varying from significant impairment to minimal discomfort. Although medical treatments can have mixed results and anxiolysis plays a crucial role, surgical intervention for true TTS is highly effective, boasting long-term cure rates that exceed 90%.[30]

Complications

The complications of TTS largely stem from its effects on a patient’s quality of life and the difficulties involved in accurate diagnosis and treatment. Ongoing, involuntary muscle contractions can cause chronic pain, distressing auditory experiences, eg, clicking or fluttering, and increased sound sensitivity (hyperacusis), which may disrupt daily activities, sleep, and mental well-being. Furthermore, misdiagnosing or failing to promptly identify TTS can lead to unnecessary testing, unsuitable treatments, or the neglect of concomitant conditions, eg, anxiety that may worsen symptoms. In rare instances, untreated or severe TTS might require surgical intervention, which comes with its own risks.