Sudden sensorineural hearing loss

Introduction:

Sudden sensorineural hearing loss is defined as 20 – 30 dB sensorineural hearing loss in atleast 3 contiguous frequencies over a period of less than 3 days. Usually this hearing loss is perceived by the patient suddenly on awakening from overnight sleep. Statistically, this type of deafness constitutes about 1% of all cases of sensorineural hearing loss.

Age incidence:

Sudden sensorineural hearing loss may affect persons of any age group. This type of deafness commonly affects patients in their 4th decade.

Associated otological symptoms:

These patients also manifest with associated otological symptoms which include:

Tinnitus – 70% of cases Vertigo – 40% of cases

Puretone audiogram: Shows the following features:

1. Downward sloping – High frequency hearing loss (common) 2. Upward sloping – Low frequency hearing loss 3. U – shaped hearing loss – Mid frequency loss 4. Flat curve – Profound sensorineural hearing loss

Management dilemma:

1. Recovery rates without treatment ranges between 40 – 70%

2. Recurrence rate with / without treatment – 30%

3. Pathophysiology is heterogeneous

4. Incidence is very rare

Causes of sudden sensorineural hearing loss:

Idiopathic – 90% cases

Non idiopathic – 10% cases

It is very important to rule out acoustic neuroma in all these patients as 4% of these patients may suffer from this disorder. Retrocochlear evaluation is a must in all these patients.

Work up: Should include

1. Pure tone audiometry

2. Impedance audiometry

3. MRI of internal acoustic canal

4. ESR

5. VDRL / FTA – Abs for syphilis

6. Serum tested for autoimmune inner ear disease

Idiopathic sudden sensorineural hearing loss:

This condition is probably multifactorial in etiology. This factor goes on to explain the high degree of variability in the therapeutic responses shown by these patients.

Two possible theories have been attributed:

Circulatory disturbance

Inflammatory reaction

It should also be stressed that these two theories are not mutually exclusive. Viral insults can cause direct neural injury, direct vascular structure injury, direct injury to red cells causing micro vascular compromise. In addition to all these responses, it can also precipitate inflammatory chain reaction.

Advocated treatment for sudden sensorineural hearing loss:

1. Steroids

2. Niacin

3. Histamine

4. Lipoflavinoid vitamins

It has been documented that patients with midfrequency hearing loss had complete recovery even without treatment. It has also been shown that 70% of patients with severe sensorineural hearing loss did not respond to therapy.

Patients with moderately severe sensorineural hearing loss responded to steroid therapy. It has been said that they lie in the “Steroid effective zone”. It is important to identify patients belonging to this group as they could benefit from steroid administration.

Steroid regimen:

Currently accepted steroid regimen is oral steroid therapy. Prednisolone is administered in doses of 1mg / kg body weight / day for 7 – 10 days. This is followed by a rapid taper of dose. It has also been said that low dose of steroids are ineffective.

Intratympaic steroid administration:

Advantages include:

1. Drug is directly administered into the site of action

2. It diffuses through round window membrane into the inner ear

3. Since inflammation / autoimmunity have been suspected to the causes, steroids could play a role.

4. There is virtually no systemic side effects

Spinal needle is used for instilling drugs directly into the middle ear cavity. Needle myringotomy is performed at two different sites in the ear drum. Both these holes should be placed in the antero inferior quadrant. They should not be close enough to avoid the complication of causing a large perforation. Drug is instilled through the second hole and the air from the middle ear cavity could be seen bubbling out through the superior opening on being displaced. Dexamethazone preferably in concentration of 10 mg/cc is used. 1ml of it is mixed with 0.1 ml of 1% xylocaine. About 0.5 ml of this solution is injected into the middle ear cavity. Injections are administered twice a week for a period of 6 weeks. Introduction of Silverstein microwick has made the job little bit simpler.