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Middle Latency Response

What is AMLR?
Auditory Middle-Latency Responses (AMLR) are related to auditory generators of the subcortical regions Na and Pa components at cortical levels. Na is considered the onset of the AMLR and Pa is considered the most robust component of the AMLR.

Why AMLR?
AMLR has the potential to offer a more complete picture of the status of the auditory system and can be used to help determine the degree of hearing loss. The most common neurological use of the AMLR is for the assessment of the functional integrity of the auditory pathway above the level of the brainstem in cases with suspected lesions and for the assessment of nonorganic hearing loss.

Further, AMLR is used in instances of traumatic brain injury, cortical deafness, multiple sclerosis, and cases of central auditory processing disorders.

Young children and infants may not present AMLR even when their auditory and neurological functions are intact, because of their higher sensitivity to stimulus rate. In general AMLR from children younger than 10 years should be interpreted with caution. It is also important to note that prior to the level of interest the auditory function should be examined and working normally, if not this will affect the AMLR results.

The stimuli used for AMLR is similar to the traditional ABR octave wide stimuli.

How to test
Patient Preparation is very important. The patient is instructed to relax and informed about the test procedure prior to testing. AMLR’s are most reliable when the patient is awake and quiet.

During sedation as with natural sleep the ALMR response is not affected.

Electrode Placement:
It is possible to obtain AMLR from with a standard ABR electrode montage. Due to the latency of the AMLR measurement, it is important to pay attention to the PAM muscle artifact, so it is not misinterpreted as an AMLR. To minimize the influence of the PAM muscle, ensure that the patient is calm and relaxed and place the electrodes on the earlobe rather than on the mastoid.

Setting up the Eclipse
The Eclipse comes with a pre-programmed protocol for AMLR testing (license) and is ready to use immediately. Protocols can be created or modified easily to fit your clinic needs. Consult your Eclipse Additional Information to learn how to create or modify a protocol.

Protocol settings:

  • An AMLR should be measured using traditional ABR stimuli, such as Toneburst 250Hz – 4kHz, stimuli from the CE-Chirp® LS family or custom wave files at an moderate intensity level.
  • For neuro diagnosis a moderate stimuli intensity below 70dB nHL is appropriate.
  • For threshold estimation, present stimuli levels as done with traditional ABR threshold testing.
  • A slower rate is indicated for younger children or for patients with cortical pathology. Normal rate for adults is below 7.1 stimuli per second.
  • Stimuli rates as low as 1 per second or 0.5 per second are required to consistently record the Pb component.

Interpretation of the AMLR result
The AMLR latency ranges from 15-80 ms and amplitude sizes ranges from 0-2uV.

An AMLR threshold recording here using Tone Burst 1kHz for threshold evaluation.

Cochlear implants
The longer latencies of the AMLR separate them from the cochlear implant stimuli artifacts seen under the traditional eABR. Therefore AMLR’s may be used to assess the efficacy of cochlear implants in activating the auditory pathway.

Reporting
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References 
Atcherson, S.R. & Kennett, S.W. (2013), Applications of middle and late latency responses, ENT & Audiology news (20)4.

Roeser, R.J., Valente, M., Hosford-Dunn, H. (2007). Audiology Diagnosis, Theime 2nded

July 2016
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