|Year : 2022 | Volume
| Issue : 2 | Page : 179-183
Middle ear myoclonus
Santosh Kumar Swain
Department of Otorhinolaryngology and Head and Neck Surgery, IMS and SUM Hospital, Siksha “O” Anusandhan University, Bhubaneswar, Odisha, India
|Date of Submission||19-Dec-2021|
|Date of Decision||27-Jan-2022|
|Date of Acceptance||02-Feb-2022|
|Date of Web Publication||09-Sep-2022|
Santosh Kumar Swain
Department of Otorhinolaryngology and Head and Neck Surgery, IMS and SUM Hospital, Siksha “O” Anusandhan University, K8, Kalinga Nagar, Bhubaneswar - 751 003, Odisha
Source of Support: None, Conflict of Interest: None
Myoclonus is an involuntary, sudden jerking of a muscle or group of muscles. Middle ear myoclonus (MEM) is an idiopathic clinical entity attributed to causing abnormal repetitive contractions of the tensor tympani and/or stapedius muscles. MEM is an uncommon disorder produced by repetitive contractions of the middle ear muscles. In MEM, the objective tinnitus is produced by synchronous repetitive contraction of the tensor tympani and/or stapedius muscle. The exact etiology of MEM remains unclear. The diagnosis of MEM is often based on the history of rhythmic and involuntary clicking or buzzing tinnitus which is invariably unilateral. The important differential diagnosis of the MEM is palatal myoclonus while other local otological diseases must be excluded with careful clinical examination. Transcanal microscopic/endoscopic middle ear exploration with the injection of botulinum toxin into the tensor tympani and stapedius muscles is helpful to relieve the symptoms of MEM. This approach is both helpful as a diagnostic and therapeutic tool that allows temporary paralysis of the middle ear muscles before providing definitive surgical treatment. The surgical section of the middle ear muscles through tympanotomy is an excellent treatment option for MEM. There are not adequate research articles available concerning MEM and mainly case reports and few case series are available during the literature search. Proper methods for diagnosis and treatment of MEM are helpful to early resolution of the symptoms and enhance the quality of life. Here, this review article is attempting to discuss the etiopathology, clinical manifestations, diagnosis, and medical and surgical treatment of MEM. Literature search for MEM was done from the database of PubMed, MEDLINE, Scopus, and Google Scholar search with the use of the words MEM, middle ear muscles contractions, symptoms of MEM, diagnosis of MEM, and treatment of MEM.
Keywords: Middle ear myoclonus, stapedius, tensor tympani, tinnitus
|How to cite this article:|
Swain SK. Middle ear myoclonus. BLDE Univ J Health Sci 2022;7:179-83
Myoclonus is an idiopathic abnormal repetitive and involuntary contraction of a muscle. Middle ear myoclonus (MEM) is defined as a rhythmic movement of the tympanic membrane secondary to repetitive contraction of the tensor tympani and/or stapedial muscles. MEM involves stapedius and/or tensor tympani muscles. MEM is an uncommon disorder and well-recognized etiology for objective tinnitus. The incidence of MEM is approximately 1.5% among new tinnitus patients. The definitive diagnosis can be done through tympanotomy and direct observation of the middle ear muscles for contractions or with the resolution of the symptoms after surgical intervention. MEM is successfully treated by selective transection of the middle ear muscles. MEM is often a diagnostic challenge. In some cases of MEM, movement of the tympanic membrane may be seen through microscope or endoscope during symptomatic muscle contractions along with supplemental audiometry confirming the rhythmic alternations in the middle ear volume. Sometimes, a presumed diagnosis of MEM is made based on patient history. The patient of MEM is initially managed by observation and reassurance. Patients with persistent symptoms may require medical therapy. The MEM is a relatively rare clinical entity and the majority of the published articles are case reports or small case series. The objective of this review article is to discuss the etiopathology, clinical manifestations, diagnosis, and treatment of MEM.
| Methods of Literature Search|| |
Literature review of the MEM was done from the database of PubMed, MEDLINE, Scopus, and Google Scholar search with the use of the terms MEM, middle ear muscles contractions, symptoms of MEM, diagnosis of MEM, and treatment of MEM. We reviewed different current articles published in national and international journals. All the articles were read and analyzed, with relevant data being extracted. A flowchart of the selected articles is in [Figure 1]. This manuscript reviews the details of MEM with its etiopathology, clinical manifestations, diagnosis, and treatment. This review article surely makes a baseline from where further prospective studies can be designed for the MEM which can help to get early diagnosis and treatment.
| Anatomical Perspectives|| |
The stapedius muscle arises from the pyramidal eminence and is inserted into the posterior surface of the neck of stapes. The stapedius muscle is innervated by the facial nerve. The tensor tympani muscle arises from the wall of the bony canal of the eustachian tube and part of this muscle also arises from the cartilaginous part of the eustachian tube and greater wing of the sphenoid. The tensor tympani muscle enters the process cochleariformis and passes laterally and inserts to the medial part of the handle of the malleus. The tensor tympani muscle is innervated by the mandibular nerve (a motor branch of the trigeminal nerve). If stapedius muscle will contract, it pulls stapes posteriorly with lateral displacement of the posterior tympanic membrane, whereas contraction of the tensor tympani muscle pulls the malleus medially and anteriorly with inward movement of the tympanic membrane. The contractions of the stapedius and tensor tympani muscles have been intended to protect from noise-induced cochlear damage and selective attenuation of the low-frequency sound component. Moderate-to-loud sound may invoke an acoustic reflex with contraction of the stapedius muscle which causes an increase in stapes annular ligament impedance and reduces middle ear sound transmission. It also attenuates frequency stimulus components which improve the intelligibility of speech at high intensities. The stapedius muscle may possess nonauditory inputs, because few persons can contract this muscle voluntarily, suggesting cortical projections to the stapedius motor neurons. The tensor tympani muscle is associated with tensor veli palatini muscle which usually controls the tension in the wall of the eustachian tube. The tensor tympani and tensor veli palatini muscles are both innervated by the trigeminal nerve, and both have an insertion in the cartilaginous part of the eustachian tube and are thought to play an important role in the ventilation of the middle ear.
| Etiopathogenesis|| |
MEM is a rare condition with an unknown etiology. MEM is an uncommon condition due to abnormal movement of the stapedius and tensor tympani muscle. The etiology is thought to originate from aberrant myoclonic contractions of the stapedius and/tensor tympani muscle. Contraction of the stapedius muscle pulls the stapes posteriorly resulting in lateral displacement of the posterior tympanic membrane while contraction of the tensor tympani pulls the malleus anteromedially resulting in the inward displacement of the tympanic membrane. Myoclonic movements are types of segmental myoclonus that involve muscles innervated from the limited part of the brainstem. Segmental myoclonus by infectious, vascular, demyelinating, traumatic, neoplastic, or idiopathic causes can result in palatal, ocular, jaw, facial, tongue, and MEM. The possible mechanism for MEM is given in [Figure 2].
| Clinical Presentations|| |
Tinnitus is a common otologic symptom that is usually associated with several ear diseases. In MEM, tinnitus is usually associated with contraction of the intratympanic muscles which is extremely disturbing to the sufferer. MEM causes the repetitive, often unilateral sound to the patient, and is also audible to the examiner. Tinnitus is characteristically described as clicking or buzzing in quality but varies widely among patients. Tinnitus can be two types such as subjective and objective tinnitus. Subjective tinnitus is more common in routine clinical practice and is the phantom perception of buzzing or ringing sound in the ears or head without the presence of an external sound source. In contrast to subjective tinnitus, objective tinnitus or somatosound arises from the paraauditory structures of the head. This symptom is less common and sound can be heard by both patient and examiner. Objective tinnitus is found in patients with vascular abnormalities, temporomandibular joint disorders, patulous eustachian tube, and tinnitus of muscle origin particularly palatal myoclonus and MEM. The tinnitus due to MEM is not much common in clinical practice. The description of the tinnitus in MEM is variable and can be described as pulsation, clicking, tapping, crackling, fluttering, or whooshing. MEM presents with pulsatile tinnitus and can affect the quality of life of the patient. It frequently causes objective tinnitus which is described as clicking or buzzing sound but the exact quality of the buzzing sound of tinnitus varies from patient to patient. Tensor tympani contraction may generate a clicking sound, whereas stapedial muscle contraction produces a buzzing sound. The history of facial nerve paralysis often affects stapedial myoclonus as the stapedius muscle has nerve supply from the facial nerve and could be affected by synkinesis. Many patients with MEM show certain triggering factors for producing tinnitus such as noise exposure and stressful events. One study showed professional musicians with MEM who are routinely exposed to loud sounds produce tinnitus. However, the exact underlying etiology for tinnitus in MEM is still not known. The important differential diagnosis of objective tinnitus is palatal myoclonus. Tinnitus due to palatal myoclonus is often bilateral. In palatal myoclonus, sound/tinnitus is due to the eustachian tube snapping open or the breaking of surface tension as well as the walls of the eustachian tube open by the action of peritubal muscles. There is another differential diagnosis of the MEM is the patulous eustachian tube or abnormal patency of the eustachian tube which gives rise to a crackling sensation in the ear but the most frequent symptom is autophony.
| Diagnosis|| |
MEM is a diagnostic challenge. Otoendoscopic examination of the tympanic membrane often shows symptomatic contractions in some cases of MEM. Both sides of the ear should be examined. Diagnostic nasal endoscopy should be done to check eustachian tube patency and palatal myoclonus. The diagnosis of MEM is not often evident by otoscopic examination. However, the rhythmic movements of the tympanic membrane due to MEM can be easily visualized during the otoscopic examination. There is controversy regarding the diagnosis of the MEM. Finding exact muscle such as tensor tympani or stapedius muscle involvement is difficult to know and there are no available objective tests which reliable to confirm. Pure tone audiometry and tympanometry are usually within normal limits in MEM. Audiological tests show irregular perturbations on acoustic reflex decay and static compliance. Long time-based tympanic membrane compliance without sound stimulation may show cogwheel or saw-toothed perturbations which may aid in diagnosis. The perturbations may be synchronized with audible clicks. Transtympanic otoendoscopic examination in an awake patient may be helpful for diagnosis. Movement of the tendon may correspond to the timing of the tinnitus. The impedance audiometry such as tympanogram, stapedial reflex, and acoustic reflex decay or static compliance may be helpful for the objective diagnosis of MEM. There may be the to-and-fro rhythmic motion of the posterior portion of the tympanic membrane found during endoscopic examination. There are perturbations in the different audiograms found in patients with MEM. Observation of the tympanic membrane with noise stimuli may be a valuable diagnostic tool for patients presenting with cracking or buzzing tinnitus in noisy conditions. Magnetic resonance imaging is useful imaging to rule out any pathological lesions in the brain. The important differential diagnosis of MEM is palatal myoclonus. The diagnosis of palatal myoclonus is done by direct oral cavity examination. Endoscopic examination of the nasopharynx may also help in the detection of palatal movement. Electromyography is also used to record palatal muscular activity.
| Treatment|| |
The first-line management of the patient with MEM is typically observation and reassurance to the patient. There are several treatment options reported for MEM including muscle relaxants, sedatives, anticonvulsants, and botulinum toxin. The treatment of MEM includes supportive therapy, as well as surgical and pharmacological treatments. Surgery is a reliable treatment option for MEM. Patients need conservative therapy using reassurance and medication which often provide resolution of the symptoms in patients with MEM. In intractable cases of MEM, the patient may require sectioning of the tendons of the middle ear muscles which provide a very promising result. The benzodiazepine is an anxiolytic drug and has a muscle relaxant effect with benefit in MEM. It ameliorates the MEM but does not inhibit it completely. Orphenadrine citrate is a skeletal muscle relaxant along with anticholinergic effects and is used in Parkinson's disease. It has been shown to reduce the MEM because of its muscle relaxant properties. Carbamazepine (used in trigeminal neuralgia, epilepsy, and primary hemifacial spasm) is also prescribed in MEM in doses up to 200 mg three times daily. However, their effectiveness has been ambiguous and the surgical sectioning of the middle ear muscles through tympanotomy is considered a straightforward and effective procedure. The most common surgical technique includes the sectioning of the stapedius and tensor tympani tendon. The surgery is usually performed under a microscopic approach or can be done by a transcanal endoscopic approach for sectioning of the endoscopic stapedius tendon. In one study, patients were subjected to sectioning of both stapedius and tensor tympani tendons where 92% of patients showed complete resolution of the symptoms in MEM during the follow-up period. One study reported on a pediatric case where bilateral sectioning of tendons of middle ear muscles failed to improve the objective tinnitus. Botulinum toxin injection to tensor veli palatini gave a resolution of the symptoms before recurrence. Gelfoam soaked with botulinum toxin placed close to stapedius tendon resolve the tinnitus. Sometimes the morbidity is associated with surgery for MEM. One study showed the risk of hyperacusis or increased vulnerability to sound after the resection of the middle ear tendon(s).
Hypnosis, acupuncture, psychotherapy, and blockage of the otic ganglion have all been attempted for the treatment of MEM without much success. The placement of pressure equalization tubes in both ears has shown no benefits. Objective clicking tinnitus has also been treated successfully with the help of tinnitus masking devices. The use of botulinum toxin is helpful as a diagnostic and therapeutic tool in the management of the MEM as it gives rise to temporary sectioning of the middle ear muscles. However, there is a chance of ototoxicity with intratympanic use of botulinum toxin. One study evaluated eight guinea pigs after intratympanic injection of botulinum toxin. The hearing thresholds were assessed through auditory brainstem response before the procedure and 1 and 3 weeks postoperatively. They also performed a histological study of the middle ear mucosa. There were hearing thresholds that remain unchanged and no evidence of any negative impacts on the middle ear mucosa. Gelfoam soaked with botulinum toxin was kept in the middle ear through a long-standing perforation which provided temporary resolution of the myoclonic symptoms. The limitations of the transcanal application of botulinum toxin involve a mechanism of action that blocks the release of acetylcholine at the presynaptic terminal of the neuromuscular junction. Because of this mechanism, the botulinum toxin should be applied directly to the belly of the muscle and not only to the tendon. Only application of this toxin at the tendon through scrapping with a needle causes partial diffuse into muscle fibers. The exposure of the middle ear muscles is better achieved with the use of a curette or micro drill of the bony margin. The traditional transcanal approach with the use of an operating microscope is helpful for a successful outcome. Pollak et al. documented the feasibility of an endoscope for improving the visualization of the stapedial and tensor tympani tendons and better treatment toward MEM.
| Technique for Application of Botulinum Toxin|| |
This technique is done in the operating room under general anesthesia. This is done through transcanal middle ear exploration. The posterior bony rim scutum is removed with the drill or house curette to expose the stapedius tendon and the tympanic membrane is raised forward to see the tensor tympani tendon. The botulinum toxin is introduced into the middle ear by a 27-gauge spinal needle. The toxin is beaded onto the needle tip and scrapped into the tendon and muscle bellies of both middle ear muscles. Then, the tympanic membrane is returned to normal position and then gelfoam is placed lateral to the repair. The patient should be reviewed after 1 month for checking about the resolution of the symptoms.
| Conclusion|| |
MEM is a rare clinical entity with unknown etiology. MEM is a difficult disease to diagnose and manage. The diagnosis of the MEM is based on typical history and examination with the active exclusion of other etiologies of tinnitus. The differential diagnosis of the MEM includes intermittent palatal myoclonus and a patulous eustachian tube. The treatment of MEM includes supportive therapy, pharmacological and surgical treatments. The application of botulinum toxin and surgical tenotomy of the middle ear muscles are the definitive treatment of MEM, but these are based on weak evidence. Tenotomy of the middle ear muscles has yet to produce long-term side effects.
| Future Research|| |
Future research for MEM should include well-designed studies with sufficient statistical power and multivariate regression analysis. The delineation of the exact etiopathology of MEM has also paramount importance. Finding the clear selection criteria for surgical intervention with proper objective measurement tools in patients with severe MEM is also important for future research. The application of topical intratympanic botulinum toxin holds a promise as animal models have not presented any ototoxicity and further research is required to confirm long-term safety on vestibulocochlear functions.
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[Figure 1], [Figure 2]