Minimum Test Battery for Assessing CANS Function - Essay Example

Minimum Test Battery for Assessing CANS Function Auditory processing is ''what the brain does with what the ear hears'' (Katz, Stecker & Henderson 4). Although the ear is responsible for picking up sound and directing it to the auditory system, auditory processing allows individuals to differentiate and interpret this signal. Hence, it is important for an individual’s Central Auditory Nervous System (CANS) to function well. Because the topic of selecting tests for assessing central auditory nervous system is complex and lengthy, we will cover only the main points. Certain tests are appropriate for specific situations and patients, a tailored set of tests should be chosen for each situation (John 13). The following general points should be considered when choosing tests to assess CANS. The sensitivity of central auditory tests is important and can be determined by testing patients with well-defined lesions of the central auditory nervous system (CANS). Using a decision matrix model, the test results from these patients can be analyzed in reference to scores (Musiek 81-82). Test selection should be guided by the intended use of the results. Specific tests may be preferred for differential diagnosis and monitoring disease progression or recovery, whereas other tests may be used to reveal functional deficits, to guide intervention planning, and to determine counseling efforts. There should also be a careful consideration of the population for testing (Katz, Stecker & Henderson 12-44). The various populations for central testing should be divided into categories. This will enhance overall test efficiency because the best tests for a target population can be used. Therefore, the test batteries for assessing CAPD are presented under several categories (Stapells & Oates, 257-280). Test Batteries for Assessing CANS Function The auditory test batteries that are used to assess CANS function or dysfunction as the case may be, falls into two major categories: Behavioral tests and Electrophysiological tests. The behavioral tests are usually divided into four subcategories: monaural low-redundancy speech tests, dichotic speech tests, temporal patterning tests, and binaural interaction tests (Picton 225). The selection of tests will depend upon a number of factors, including the age of the individual being assessed, the specific auditory difficulties the individual displays, the individual’s native language and cognitive status, and so forth. Electrophysiological tests are measures of the brain's response to sounds (Blaettner et al 179-183). Some electrophysiological tests are used to evaluate processing lower in the brain particularly in testing auditory brainstem response, whereas others assess functioning higher in the brain such as middle latency responses, late auditory evoked responses, auditory cognitive or P300 responses (Musiek & Pinheiro, 7-10). The results obtained on these tests are compared to age-appropriate norms to determine if any abnormalities exist. The pure tone audiometry, speech audiometry, and acoustic immitance continue to be important test batteries for hearing assessment. New technologies such as ABR, EcoG, and OAEs have become the latest addition to the clinical audiologic test battery. These tests are used to describe the neurological or mechanical functioning of the auditory system (Hall & Antonelli 1670). Test-retest consistency is important, especially when monitoring a patient’s changes over time. However, a test’s reliability often cannot be determined using a population of patients with CAPD. Since the nervous system by nature changes constantly when pathology is present, brain involvement of auditory regions also exhibit changes in auditory processing function (Musiek 79-83). Therefore, test-retest stability must be established on subjects who have no damage to the central nervous system. In children, neuromaturation mediates changes in brain function. Hence, age-appropriate norms must be established. Assessment of the CANS has been advanced by the development of the compact disc recording of tests (Musiek et al 8-10). Developed by research teams at the Long Beach and West Los Angeles VA Medical Centers, the Dartmouth-Hitchcock Medical Center, and the University of New Hampshire, the CD contains experimental and clinically known procedures of unprecedented acoustic quality. This CD includes the following tests: MLD, dichotic musical chords, 24 November 1994 AJA dichotic nonsense syllables, dichotic digits, dichotic sentence identification, segmented, alternated CNCs, low- and high-pass filtered words, frequency and duration pattern perception, time-compressed speech, and time-compressed speech with reverberation. The acoustic quality of the test materials is an important consideration in the selection of central auditory tests, and CDs and CD players provide a clear improvement in quality. ABR, OAE, and Acoustic Reflex The Auditory Brainstem Responses (ABR) test is a useful diagnostic tool for measuring hearing when more conventional hearing tests cannot be used (Cone-Wesson et al 173-187). The ABR is the most efficient audiologic test for pontine involvement. The ABR interwave intervals are more useful indices in patients with brainstem lesions, as compared with patients with acoustic tumors. This is because patients with brainstem lesions often have better hearing sensitivity than do patients with acoustic tumors. Thus, ABR test results are more likely to demonstrate waves I, III, and V. Conversely, interaural latency differences (ILD), another ABR index, do not appear to be as highly sensitive to brainstem lesions as are interwave intervals. Administration time is approximately 40 to 50 minutes. ABRs may be used to diagnose certain auditory conditions. This type of testing can provide a healthcare professional with very useful information about hearing loss in a patient. This technique is especially helpful when testing infants and newborns that cannot yet respond to behavioral testing (Luts 143-157). It may also be helpful to test adult patients with a certain degree of mental impairment, such as the autistic and the developmentally delayed. ABR testing can help determine the amount and type of hearing loss at specific frequencies, for example hearing threshold, depending on the cause of hearing impairment. ABR testing provides information of the complete hearing pathway, including the neural pathways in the brainstem, providing a more complete functional test, less susceptible to acoustical noise interference. Required tests before ABR are Air and Bone Pure Tone Audiogram. Optional tests are speech audiometry, otoacoustic emissions, and tympanogram. The sensitivity of ABR is 85% and the specificity is 90-95%. OAE testing is another non-behavioral or objective measure that has been used for early detection of ototoxicity. OAEs can be elicited by clicks or tonal signals. Unlike ABR testing, OAE only tests for cochlear function. The sensitivities are only slightly less than ABR for OAE testing (Pastor 11624-11627). The acoustic reflex threshold is defined as the lowest possible intensity needed to elicit a middle ear muscle or stapedius contraction. The ASR test functions to screen individuals for middle ear disease. ASR measurements may also be useful in determining the site of a seventh nerve lesion. Works Cited Blaettner, U., Scherg, M., and von Cramon, D.. “Diagnosis of unilateral telencephalic hearing disorders”. Brain 112 (1989) 177–195. Hall, J. and Antonelli, P. Assessment of the Peripheral and Central Auditory Function. Philadelphia: Lippincott, 2001. Katz, J., Stecker, N.A., and Henderson, D. Introduction to Central Auditory Processing. St. Louis: Mosby Year Book, Inc., 1992. Musiek, F. (1983). “Assessment of central auditory dysfunction: The dichotic digit test revisited”. Ear and Hearing, 4, 79–83. Musiek, F., Baran, J., and Pinheiro, M.. “P300 results in patients with lesions of the auditory areas of the cerebrum”. Journal of the American Academy of Audiology, 3 (1992), 5–15. Stapells, D.R. and Oates, P. “Estimation of the Pure-Tone Audiogram by the Auditory Brainstem Response: A Review”. Audio-Neuro Today. Dec. (1997) 257-280. Cone-Wesson B., Dowell R.C., Tomlin D., Rance G., Ming W.J.. “The Auditory Steady-State Response: Comparisons with the Auditory Brainstem Response”. Journal American Academy of Audiology Volume 13 (2002) 173-187. Luts, Heleen A, Desloovere, Christian B, Wouters, Jan. “Clinical Application of Dichotic Multiple-Stimulus Auditory Steady-State Responses in High-Risk Newborns and Young Children”. Audiology & Neuro-Otology Volume 11 Number 1 (2006) 24-37 Picton, Terence W. “Source Analysis of Auditory Evoked Electromagnetic Fields”. International Journal of Bioelectromagnetism Volume 4 Number. 2 (2002) 225 – 228 John, Michael Sasha. “Stimulus Setup Instructions”. Toronto, Canada: Rotman Research Institute, 2003. Pastor, Maria A., Artieda, Julio, Arbizu, Javier, Valencia, Miguel and Masdeu, Jose C.. “Human Cerebral Activation During Steady-State Visual-Evoked Responses”. Journal of Neuroscience Volume 23 Number 37 (2003) 11621-11627. Read More