Tinnitus management using intratympanic medications

Definition:

Tinnitus is defined as abnormal sound heard in the ear. It can be divided into two types:

Subjective tinnitus: where the sound is heard only by the patient and not by the physician.

Objective tinnitus: Is heard both by the patient as well as the examining physician. One common example of objective tinnitus is palatal myoclonus.

The term tinnitus is derived from the Latin word tinnire which translated means ringing sound. Tinnitus can occur alone or in combination with sensorineural hearing loss. People affected belong to the 5th and 6th decade age groups. It is a very difficult condition to manage because of its multifactorial etiology.

Management of tinnitus an overview:

Tinnitus could be managed by:

1. Hearing amplification (use of hearing aids)

2. Use of tinnitus maskers

3. Use of oral drugs

4. Tinnitus retraining therapy

To this list recently intra tympanic medications have also been added. This should infact be considered in selected cases.

Schuknecht first used intra tympanic aminoglycosides (Streptomycin) for treatment of Meniere's disease. Because of its ototoxic effects this therapy had immediate effect on tinnitus. Beck later used gentamycin in tinnitus management. This drug gained in popularity because of its ability to preserve hearing. Lignocaine and steroids were also used with success in the management of tinnitus.

Use of intratympanic lignocaine in the management of tinnitus:

Lignocaine belongs to a drug group called amides. Its mechanism of action is through sodium channel blockade at the level of neurons. It also has a profound analgesic, antiarrythmic and anticonvulsant properties. It has this unique ability to silence the hyperactive neurons responsible for the production of tinnitus.

Event hough it was highly effective in the management of tinnitus, it had certain unpleasant side effects like vertigo, nausea and vomiting which necessitated hospitalisation of the patient.

Silverstein microwick

Use of intratympanic corticosteriods in the management of tinnitus:

Corticosteriods are well known for its anti inflammatory property. Steriod receptors have been demonstrated in the inner ear. It also increases the blood supply to the cochlea. It is this property which has been attributed as the cause for its effect on tinnitus. The advantages of intra tympanic adminsitration of steriods is as follows:

1. When administered intra tympanically, it is devoid of its systemic toxic effects.

2. There is an immediate increase in concentration of this drug in the inner ear. There is virtually no latent period.

Methylpredinsolone has been found to have the best effect in the reduction of tinnitus because of its ability to penetrate into the inner ear fluids though the round window membrane.

Factors influencing the passage of drugs through the round window:

1. Normal round window membrane

2. Presence of inflammation around round window membrane increases its permeability to the drug.

3. Obstruction due to eustachean tube block: This allows the drug to stay a long time within the middle ear cavity facilitating inner ear penetration via the round window membrane.

4. Molecular weight of the drug administered: Lesser the molecular weight of the drug better is the penetration.

5. Liposolubility: The more liposoluble the drug the better is its penetration through the round window membrane.

Studies have shown that steriods have better effects in controlling the tinnitus caused by Meniere's disease, while lignocaine has better effect in controlling tinnitus associated with labyrinthine vertigo.

Dexamethasone can be perfused through the middle ear in a dose of 4mg/ml. This drug can be instilled into the middle ear through a tympanotomy incision. Injections can be repeated once a week till the patient is symptom free. Grommets can be introduced to facilitate repeated injections of this drug.

Gentamycin can be administered intra tympanically in doses of 40mg/ml. It can be repeated at weekly intervals till the patient is symptom free.

Modern middle ear drug delivery systems:

The aim of this delivery system is to predictably deliver drug directly over the round window membrane to facilitate easy absorption. The Silverstein micro wick has been specifically designed for this purpose. The main advantage of this system is that after the initial administration of the drug by the physician the patient himself can administer the drugs at home at specified intervals. The microwick absorbs the medication and transports it directly to the round window membrane.

The microwick is made up of polyvinyl acetate. It measures 1mm in diameter and about 9mm long. It can be easily inserted through a grommet. As a first step grommet must be inserted into the round window area under local anesthesia. Round window niche is identified as a dark area just posterior and inferior to the umbo. Microwick can easily be inserted through this ventilation tube in such a way that it lies in contact with the round window membrane. After the first administration of the drug patient himself can administer the drug as ear drops two or three times a day as advised. The only precaution is that the patient must lie with the drug adminstered ear facing up for at least 5 minutes to enable adequate drug perfusion into the middle ear.

Figure of ear drum showing the round window area

After treatment the microwick can easily be removed without anesthesia using a micro cup forceps.

Indications for intratympanic medications:

1. Meniere's disease

2. Sudden sensori neural deafness (steriod is used)

3. Tinnitus

Complications of intratympanic medications:

1. Intense giddiness

2. Vomiting

3. Middle ear infection

4. Residual perforation

Pitfalls of microwick therapy:

1. Accurate placement of the microwick over the round window area is a must.

2. Laser tympanotomy is preferred to conventional one because of the blood less field. This is a must for accurate placement of the wick. When the area is moist insertion of the wick becomes difficult because it swells up on exposure to moisture.