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BRAINSTEM EVOKED RESPONSE AUDIOMETRY (BERA)

Definition: Brainstem Evoked Response Audiometry (BERA) is an objective electrophysiological test measuring response in the brain waves that are stimulated by a clicking sound to check the central auditory pathways (hearing) of the brainstem. It is a non-invasive technique to find the integrity of central auditory pathways through the VIIIth nerve, pons and midbrain. Indications:
  1. Nervous system abnormalities.
  2. Children with hearing loss.
  3. To assess neurological functions.
  4. Malingering patients.
  5. Suspected acoustic neuroma.
  6. Central pontine myelinolysis.
Procedure:
  1. The test is done in an air-conditioned room.
  2. Patient is asked to wash the hair the night before the test.
  3. Patient in lying down position, eyes closed and preferably asleep.
  4. Infants and small children need to be administered sedatives like triclofos sodium in a
  5. dose of 50 mg per kg of body weight or promethazine hydrochloride in a dose of 0.5mg per kg of body weight so that the child is deeply sedated during the test.
  6. Electrodes are placed on the patient’s scalp, along the vertex and on each earlobe.
  7. Earphones are put on the ear. The patient hears a clicking sound between 10 and 40 clicks per second through the earphones.
  8. The electrodes pick up the brain’s response and record it on the graph.
  9. It measures hearing sensitivity in the range of 1000–4000 Hz.
  10. In a normal person, seven waves are produced in the first 10 ms.
  11. The first, third and fifth waves are most stable and are used in measurements.
  12. The waves are studied for absolute latency, inter-wave latency (usually between wave I and V) and the amplitude.
  13. Wave V is the most reliable and easily identifiable wave in the BERA tracing.
Interpretation:  A series of waves are recorded in BERA test. These waves arise from:
  • Wave I         Distal part of CN VIII
  • Wave II         Proximal part of CN VIII near the brainstem
  • Wave III         Cochlear nucleus
  • Wave IV         Superior olivary complex
  • Wave V         Lateral lemniscus
  • Waves VI         Inferior colliculus
  • Waves VII        Medial geniculate body
The morphology and amplitude of the wave forms are measured.
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Absolute latency:
Wave I 1.55- 1.75 millisecond
Wave III 3.8 millisecond
Wave IV 5.5- 5.85 millisecond
Interwave latency:
Interwave latency Normal value (milliseconds) Criteria for abnormality (milliseconds)
I-V 4 More than 4.4
III-V 2 More than 2.4
I-III 2 More than 2.4
Interaural latency:
Parameter measured Normal value (milliseconds) Criteria for abnormality (milliseconds)
Interaural latency difference of wave V Less than 0.3 More than 0.3

This test has minimal discomfort and there are no risks involved.

Abnormal test results are indicative of:

1) Hearing loss.
2) Multiple sclerosis.
3) Cerebrovascular accidents (stroke).

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