8 August 2018

Rarely heard – unusual syndromes underlying tinnitus

Clinical Patients

In the second of our two-part series on tinnitus, Dr Sean Flanagan examines the rarer syndromes that can cause the symptom.

SUDDEN SENSORINEURAL HEARING LOSS

This involves a sudden onset of tinnitus and hearing loss or a blocked ear. 

This can occasionally represent sudden sensorineural hearing loss syndrome. Often patients notice the tinnitus and a full or blocked feeling but do not appreciate that their hearing is also down.  

This condition in most cases is thought to be related to a viral reactivation phenomena and rapid institution of steroid therapy can help salvage some of the hearing loss. This presentation is one where an urgent referral to an ENT surgeon and formal audiometry is required. 

Occasionally steroid injection into the middle ear can help salvage hearing and an MRI scan is usually required as a vestibular schwannoma can occasionally present in this way. 

When the patient is left with a marked unilateral hearing loss, devices such as a bone anchored hearing aid, or a BiCros hearing aid can be used to reroute an auditory signal presented to the deaf ear across to the normal hearing ear.

If the severe hearing loss is accompanied by significant tinnitus cochlear implantation has recently been shown to be a very efficacious management option.

VESTIBULAR SCHWANNOMA

When a patient presents with asymmetric hearing loss or single-sided tinnitus then imaging of the brain and cerebellopontine angle is indicated to exclude the  presence of central pathology, the most common of which is a vestibular schwannoma (acoustic neuroma). 

These are benign tumours arising from the vestibulo-cochlear nerve. They are the commonest tumour of the cerebello-pontine angle at 80% and represent about 9% of all intracranial tumours. 

The natural history of growth is critically important in the formulation of a management paradigm. It has become apparent that a large cohort of tumours either do not grow or grow very slowly.

Treatment algorithms include conservative surveillance, microsurgical removal employing either hearing conservation or hearing destructive approaches and radiotherapy. 

We now consider quality of life outcomes, as well as hearing and facial nerve conservation rates. 

The critical decision to be made is when to intervene. One of the most important questions to answer revolves around:

 1) what aspect of the tumours existence most disables the patient, and;

2) does early intervention realistically improve or arrest the progression of this disability without introducing the morbidity of the treatment itself. 

The two most easily quantifiable variables are hearing, scored via PTA and SD, and facial nerve outcomes using the House Brackman (HB) scale from normal I, to complete paralysis, VI. 

The increased use of quality of life, both specific, such as hearing disability scores, and generalised such as SF-36, are  allowing us to make more informed decisions and recommendations for appropriate management. 

The conservative watch-and wait-approach has now been widely canvassed in the literature. Most of the recommendations for this mode of management revolve around the older patient, or those with significant co-morbidities.  To operate early, with the aim of hearing preservation, in many cases will lead to worse patient outcomes. 

Conservative management 

The “failure rate” of conservative therapy is now 15%. It is important to note that even for those tumours that fail initial conservative treatment, quality of life outcomes are not worse than if treated at initial presentation. 

When to proceed to surgery

1. Documented growth: Usually greater than 2 to 4mm per year. Intervening when the tumour is less than 15mm in the Cerebellopontine angle gives the best results. 

2. Brainstem compression 

3. Significant vestibular disturbance: occasionally even for small tumours. 

Optimal outcomes are achieved by a highly experienced, multi-surgeon team. The results of micro-surgical removal are now very good, but it remains a major intracranial procedure not to be taken lightly, and audiologic and vestibular rehabilitation is very important. 

Radiotherapy: Steriotactic radiotherapy is an option for small tumours with documented growth, in patients in whom surgery is contra-indicated, and in cases where residual tumour shows regrowth.

MENIERE’S DISEASE

Meniere’s  disease is a disorder affecting inner ear homeostasis, classically manifested by episodic vertigo lasting hours, fluctuating hearing loss, tinnitus and aural fullness. Rarely sudden drop attacks can develop. 

It is a rare but debilitating condition, and essentially represents a situation where the inner ear is hypersensitive to a wide range of triggers. 

Multifactorial management is essential with minimisation of emotional and physiologic stress and reduction of dietary salt the first step. 80% of cases can be managed with these simple measures. 

More interventional options exist, all the way up to the transection of the vestibular nerve, but rehabilitation of hearing and vestibular function is equally as important. 

CONDUCTVE TINNITUS
(often classified as objective tinnitus)

When a patient describes the sound of tinnitus as resembling pulsation, clicking or related to breathing or swallowing, a mechanical or structural lesion is more likely and must be ruled out.  In general terms this can be divided into pulsatile, muscular or related to the Eustachian tube.

The commonest underlying cause of pulsatile tinnitus is the most benign and relates to a degree of Eustachian tube dysfunction. This often occurs after a head cold and is related to pulsations being transmitted down a partially blocked Eustachian tube to the middle ear. In severe cases the middle ear fills with fluid causing an effusion which can also become infected causing an acute otitis media. 

Clicking and crackling on swallowing are also described and reflect the tube starting to re-open. This is usually self-limiting and is often helped by using topical nasal therapies, and if it completely resolves requires no further investigations.

A rarer form of tinnitus is called patulous Eustachian tube and patients describe a sensation of autophony and hearing their own breathing. Diagnosis is made by observing excursions of the tympanic membrane with unilateral nasal breathing.

When the description involves bilateral symptoms then hyperdynamic  syndromes must be considered. These include  pregnancy, thyrotoxicosis, anaemia, anxiety, hypertension and Paget’s disease. 

 Another diagnosis to consider in bilateral pulsatile tinnitus is benign intracranial hypertension, although this can also cause unilateral symptoms.

True pulsatile tinnitus originates from vascular structures within the head, skull base, neck , and thoracic cavity, and it is transmitted to the cochlea by bony or vascular structures.

Arterial: Cardiac causes and carotid artery disease can usually be identified on auscultation and/or via cardiac echo and carotid and vertebral artery duplex studies. 

A mass identified behind the tympanic membrane and/or the presence of a conductive hearing loss suggests a paraganglioma (glomus tumour) arising from the middle ear or extending up from the jugular foramen, otosclerosis,  an aberrant blood vessel coursing through the middle ear or a meningoencephalocele. 

Removing even this relatively small tumour may well result in sacrifice of the lower cranial nerves so often a watch and wait approach is initially employed. If there is rapid growth and or the tumour itself causes damage to the lower cranial nerves, interventional treatment is then considered.

 Slow loss of function allows the body to better compensate for this neural damage.

With a normal otoscopic examination the pathology is more likely related to an arteriovenous fistula or arterovenous malformation, a tortuous ICA, dissection or aneurysm formation of the extra or intracranial segment of the ICA and fibromuscular dysplasia

Venous: The sound that the patient often describes is more like a machinery or continuous hum. Benign raised intracranial pressure, abnormalities of the jugular bulb abnormalities, stenosis of the transverse of sigmoid sinuses, abnormalities of other draining veins of the skull base, and other causes of raised intracranial pressure are possibilities.

Causes include post infectious thrombosis with partial recanalisation and prominent arachnoid granulations. Most cases are identified by MRV. When symptoms are severe, consideration of direct venography is made, allowing more accurate diagnosis and measurement of trans-stenotic pressure gradients.  

Clues as to the cause of the tinnitus can be gained by otoscopy and auscultation of the chest and neck. If occlusion of the internal jugular vein minimises the sound then a venous cause is more likely.

INVESTIGATIONS

Usually both a CT scan of the skull base and MRI, MRA, MRV are required. If there is an abnormality of the middle ear a CT scan is usually the first line investigation otherwise an MRI is ordered primarily. 

These extensive investigations are important to rule out an arteriovenous fistulas (AVF),  arteriovenous malformations (AVM), vascular tumours of the skull base and vascular stenoses as these pathologies can lead to serious sequelae.  

TREATMENT

Treatment is obviously specific to the underlying pathology, but endovascular approaches are usually used for dural AVFs, and stenting in selected cases of venous sinus stenosis is effective. 

Vascular tumours are often amenable to safe removal, especially if arising from the middle ear, but may involve significant collateral damage to the lower cranial nerves for those arising from the jugular foramen so a period of conservative observation is usually employed.  Aberrant ICA and abnormalities of the IJV and jugular bulb are almost always also treated conservatively.

Otosclerosis is imminently treatable either surgically via a stapedectomy, or occasionally with a hearing aid. and rarer conditions such as a meningoencephalocele require surgical repair to prevent the risk of meningitis.

Treatment of BIH often involves weight loss and a trial of acetazolamide in concert with a neurologist. It is rare that more interventional management is required. Not infrequently, all these investigations are unremarkable and the diagnosis of idiopathic or essential tinnitus is then made. Similarly to subjective tinnitus, often reassurance that there is no serious pathology is all that patients are searching for.

SPECIAL CASES

Conductive hyperacusis of the superior semicircular canal dehiscence syndrome. In this rare condition patients often describe hearing extreme transmissions of footsteps to the ear, and even the sensation that they can hear their eyeballs move. It is also associated with noise and pressure related disequilibrium. It is due to a connection between the membranous labyrinth of the superior semicircular canal and the dura, due to lack of a bony covering in this area. 

It is diagnosed on CT scanning of the petrous temporal bone in the plane of the superior semicircular canal and measuring abnormalities in a VEMP test (vestibular evoked myogenic  potentials). Treatment is usually conservative, but in severe cases we consider surgical resurfacing of the dehiscent superior semicircular canal. 

MUSCULAR CAUSES

Myoclonic contractions of the tensor veli palatini, levator veli palatini, salpingopharyngeus, and superior constrictor for palatal myoclonus, and tensor tympanic and stapedius muscles for middle ear myoclonus are another uncommon cause of tinnitus.

It is usually a clicking sound ranging between 10 and 240/min, which can occasionally be confused with a pulsatile sensation. Very rarely this can be associated with an underlying neurological disorder so MRI imaging of the brain and brainstem is recommended. 

Again, explanation and reassurance is the most important treatment, with interventional management occasionally employed.

First-line therapy now involves botox injection into the muscle belly for palatal myoclonus, with surgical section of middle ear muscles rarely indicated. 3, 21,22

References: 

1. Bhimrao SK, Masterson L, Baguley D. Systematic review of management strategies for middle ear myoclonus. Otolaryngology – Head & Neck Surgery;146:698-706

2. Park SN, Bae SC, Lee GH, et al. Clinical characteristics and therapeutic response of objective tinnitus due to middle ear myoclonus: a large case series. Laryngoscope 2013;123:2516-20.

3. Hidaka H, Honkura Y, Ota J, Gorai S, Kawase T, Kobayashi T. Middle ear myoclonus cured by selective tenotomy of the tensor tympani: strategies for targeted intervention for middle ear muscles.