Middle ear myoclonus (MEM) syndrome
Middle ear myoclonus or middle ear myoclonus (MEM) syndrome is a form of tinnitus. It is the perception of sound without an appropriate external source. Myoclonus is the rhythmic contraction of a muscle and in the case of MEM syndrome of either, or in rare cases both, of the middle ear muscles. The “clicking” or “buzzing sound” can be severely distressing to patients.
The middle ear muscles
The middle ear contains muscles namely the stapedius muscle and the tensor tympani muscle. They attach to different ear bones( ossicles) and are innervated by separate cranial nerves. The function of the stapedius muscle is to stiffen the ossicular chain at the level of the stapes and is likely to attenuate external sound in order to protect the cochlea. The tensor tympani muscle attaches to the malleus an by contracting stiffens the ossicular chain at the level of the malleus and tympanic membrane. This action leads to the attenuation of internal body sound generated when swallowing, chewing and talking. Another function of these muscles is to produce movements at the ossicular joints in order for the joints to stay healthy and work effectively in protecting the tympanic membrane against ambient pressure changes.
The clinical picture of MEM syndrome.
Patients present with the history of a “clicking” or “buzzing” sound in the ear. The sound may also be described as bubbling, thumping, whooshing, gushing, ticking, crackling, throbbing or tapping. In rare cases the noise may be heard by another person. This is then referred to as objective tinnitus. It is difficult to distinguish between myoclonus of the stapedius muscle and myoclonus of the tensor tympani( tensor tympani or TT syndrome) based on the reported characteristics of the sound. Although a “clicking” sound is generally associated with TT syndrome and a “buzzing” sound with stapedius muscle myoclonus a definite diagnosis can only be made with direct visualisation of the muscle spasm.
The examination is usually normal but in some cases a rhythmic movement of the tympanic membrane may be seen, sometimes initiated by eye blinking. Audiometry is not used for diagnosis but in some cases long-term audiometry may show a characteristic appearance. Conditions that may mimic MEM syndrome include palatal myoclonus and patulous eustachian tube. In palatal myoclonus the contraction of the soft palate can be visualised and in a patulous eustachian tube patients can hear their own voice (autophonia) and rhythmic movement of the tympanic membrane in tandem with breathing can be visualised.
The cause of MEM syndrome.
In the majority of cases the cause is unknown. Anxiety plays a major role and is believed to lower the threshold for the occurrence of the muscle contractions. Other conditions that may be responsible for objective tinnitus and need to be excluded include abnormal blood vessels, atherosclerosis, vascular tumours such as paraganglioma and multiple sclerosis.
Management of MEM syndrome.
After exclusion of other conditions treatment options include oral medication, surgery and the local application of botulism toxin. Medication aim to reduce the myoclonus and some drugs like benzodiazepines have an additional anti- anxiety effect. Surgical treatment comprises of tympanotomy and surgical section of the muscle tendons (tenotomy). This is non-reversible and therefore the diagnosis must be clear, medication not affective and the responsible middle ear muscle identified with certainty.
Botulinum toxin is used in medicine to treat muscle disorders characterised by spasm and overactivity. It may be locally applied or injected into the muscle and although the effect is not permanent may help to confirm the diagnosis and identify the correct muscle for possible later surgical section (tenotomy). Tinnitus masking devices, zygomatic pressure manoeuvres and psychotherapy are less effective means of treatment.