Monday, December 27, 2010

Sensorineural Hearing Loss: Features, Aetiology And Management

SNHL results from lesions of the cochlea or CN VIII or central auditory pathway. It may be present at birth(congenital) or start later in life (acquired).

The characteristics of sensorineural hearing loss are:

  1. Rinne +ve ie AC>BC
  2. Weber lateralised to better ear
  3. Bone conduction reduced on Schwabach and ABC test
  4. More often involving higher frequencies
  5. No gap between air and bone conduction curve on audiometry
  6. Loss may exceed 60 dB
  7. Speech discrimination is poor
  8. Difficulty in hearing in presence of noise.

Aetiology:

Congenital Causes:
Acquired Causes:
  • Noise-induced - prolonged exposure to loud noises (>90 dB) causes hearing loss which begins at 4000Hz (high frequency). The normal hearing range is from 20 Hz to 20,000 Hz.
  • Presbycusis - age-related hearing loss that occurs in the high frequency range (4000Hz to 8000Hz).
Diagnosis:
  1. History: whether disease is congenital or acquired, stationary or progressive, associated with other syndromes or not, whether familial or not.
  2. Severity: whether mild, moderate, moderately severe, severe, profound or total. can be determined by audiometry.
  3. Type of Audiogram: whether loss is of high frequency or low frequency or mid-frequency or flat type.
  4. Site of Lesion: whether cochlear or retrocochlear or central
  5. Laboratory Tests: X-ray or CT scan of temporal bone for evidence of bone destruction (congenital cholesteatoma,  glomus tumour, middle ear malignancy or acoustic neuroma), blood counts(leukemia), blood sugar(diabetes), VDRL(syphilis), thyroid function tests(hypothyroidism), kidney function tests, etc
Management:

Early detection of SNHL is important as measures can be taken to stop its progress or reverse it or to start an early rehabilitation.

Syphilis of ear is treatable with high doses of penicillin and steroids.

Hearing loss of hypothyroidism is treatable with replacement therapy.

Serous labyrinthitis can be reversed by treating middle ear infection.

Early management of Meniere’s disease can prevent further episodes of hearing loss and vertigo.

SNHL due to perilymph fistula can be corrected surgically by sealing the fistula in the oval or round window by fat.

Ototoxic drugs should be discontinued, if found to be causing hearing loss.

Noise induced hearing loss can be prevented from further deterioration by removal of the person from the noisy surroundings.

Rehabilitaion of hearing-impaired with hearing aids.

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