Opinion | April 2018 Hearing Review

As with any branch of auditory science, research on CAPD continues to be pursued in many different areas. However, there is robust scientific evidence pertaining to the clinical existence, diagnosis, and treatment of CAPD. This short article provides a literature review for what might be viewed as six key tenets related to CAPD.

There is widespread agreement among audiologists and our professional associations regarding the validity of the diagnosis of central auditory processing disorder (CAPD), the sensitivity of the diagnostic battery used to identify the disorder, and the efficacy of treatment for CAPD. This paper provides the evidence base for audiologists’ agreement supporting the clinical existence of CAPD, including the diagnosis and treatment of this disorder.

Musiek et al1 and Moncrieff2 provided substantial evidence that audiologists recognize the importance of assessment of the central auditory system to fully evaluate auditory or hearing function. The American Medical Association (AMA) has recognized the validity and clinical utility of CAPD by including it as a diagnosis code in the ICD-10. This ICD-10 code (H93.25) is recognized by Medicare, and the US Department of Veterans Affairs recognizes this code for testing and treatment. The Ninth Circuit Court of Appeals recently designated CAPD as an “Other Health Impairment” (OHI) under The Individuals with Disabilities Education Act (IDEA) and audiologists were named as qualified providers to diagnose CAPD.3,4 The Canadian Supreme Court in Pitcher v. Brown (2015)5 recognized CAPD as a valid clinical entity, despite arguments to the contrary. 

Diagnosis and treatment of CAPD falls in the audiology scope of practice.6 While the scientific process within our profession continues to improve the evaluation and treatment of CAPD, most audiologists concur on the following points based on extensive, peer-reviewed published evidence, our collective practice-based clinical experience, and the positions of our major professional organizations:

1) The auditory sensori-perceptual system is comprised of the peripheral and central systems. These systems are interdependent, influencing each other.

2) Auditory signals are transformed into neural impulses. Auditory processing refers to the mechanisms which establish the neural code. These mechanisms preserve, refine, analyze, modify, organize, and interpret or process the input from the auditory periphery along intensity, frequency, and time domains.

3) Central auditory processing is fundamental to listening, which is a key process underlying communication and learning.

4) Treatment for deficit-specific weaknesses of central auditory processing has been shown to be effective.

5) Patients seek funding for CAPD evaluation and treatment. There is ample evidence to demonstrate that diagnosis of CAPD is sensitive and specific using available tests and procedures and that intervention for CAPD is efficacious.

6) Audiologists support serving patients with CAPD.

1) The auditory sensori-perceptual system is comprised of a peripheral and a central system. These systems are interdependent, influencing each other. Central auditory processing disorder has also been known as auditory processing disorder (APD), a term that acknowledges the interaction between the periphery and the central auditory systems.7-9 We use the term “CAPD” because CAPD reflects the origins of the disorder in the central nervous system and this is the term listed in the ICD-10 diagnosis codes. Audiologists recognize that CAPD is a term that involves multiple subprocesses and that deficit-specific identification and treatment is optimal to effectively and efficiently provide intervention for CAPD.

The peripheral and central auditory systems have been described with regards to anatomic site and function.10-13 The processing deficits of the central auditory system have been validated in animals and humans with confirmed neurological lesions.14-19 For example, damage to both auditory cortices can render a person totally deaf even when the cochleae are intact.20

CAPD is seen in persons with listening and learning difficulties with neurological lesions beyond the cochlea.10,14 These patients have specific difficulties with some mechanism of the auditory system used to analyze sound. Central auditory processing deficits have been identified in persons who have experienced, for example, traumatic brain injury (TBI) via blast exposure, motor vehicle accidents, strokes, sports- or accident-related concussions, and neurodegenerative diseases.21-29

CAPD also is identified in children who have listening, reading, learning, and language difficulties with no specific site of central pathology identified.30-55 These children are inferred to have more diffuse neuroanatomic abnormalities.56 Children with listening difficulties also frequently present comorbid learning difficulties, as well as ADHD, language, and reading problems.46,51,53,57-59 These comorbidities are not unexpected given the extensive organization of the auditory system which shares neural substrate and processing with other domains.60 This organization underlies both comorbid presentations, as well as interactions between sensory and cognitive systems.61-68 For example, reading is known to be auditory based, and many persons with CAPD have reading difficulties.31,32,34,36,37,40,41,43,45,54,55,69-71

As is true for any medical science, considerable audiologic efforts are continually invested in refining and expanding the evaluation and treatment of CAPD. Challenges to aspects of CAPD72,73 have been countered with extensive evidence.3,4 Accumulated clinical and basic evidence supports the validity and utility of the CAPD diagnosis. Audiologists are uniquely qualified to identify and treat CAPD, and we are the appropriate professionals to help patients with CAPD. As a profession, we recognize the remarkable complexity and interaction among audition, language, attention, and cognition.

2) Auditory signals are transformed into neural impulses. There are central mechanisms that process the input from the auditory periphery along intensity, frequency, and time domains. Central auditory processing refers to the brain’s essential function to decode patterns of electrical impulses critical to our ability to communicate effectively in our everyday environment. Noted auditory neuroscientist Nina Kraus, PhD, explained that the currency of the central auditory system is electrical impulses.74 The brain is the banker of this currency. Neural impulses give rise to a host of auditory processes: detection, localization, discrimination, temporal ordering, temporal resolution, temporal sequencing, binaural integration, binaural separation, spatial stream segregation, and auditory closure. These processes can be assessed and deficits identified using sensitive and specific tests and procedures.75 Perhaps the most well-known example is dichotic listening, which has been well-substantiated in the literature to identify hemispheric and inter-hemispheric processing deficits. The evidence that dichotic listening procedures can identify deficits in the central auditory pathways has been demonstrated by researchers across the world using a variety of languages.14,49,55,76-78

3) Central auditory processing is fundamental to listening. Listening is a key process by which we learn. Children need to hear and interpret sound in order to develop spoken language and succeed academically.33,35-37,79 Barker et al34 demonstrated electrophysiologically and behaviorally that intact central auditory function is fundamental for reading development. Auditory training has been an effective tool for people with deficits in detection (hearing loss) for over 100 years. Auditory training for persons with CAPD is also effective.39,42,46,51-53,58,70,71,80-86 A minimal level of intelligence, attention, and motivation underlies the success of any behavioral training program, including auditory training.32,36,42,87-89

Central auditory processing is fundamental to effective listening. CAPD and listening difficulties are frequently linked to learning deficits. Therefore, it is essential that audiologists identify and develop treatment plans for CAPD. Early diagnosis and treatment for CAPD may prevent, or at least minimize, its detrimental effects on listening, learning, language processing, and reading.

4) Treatment for central auditory processing deficits is shown to be effective. CAPD can be evaluated behaviorally, with treatment outcomes measured both behaviorally and electrophysiologically. In the United States, behavioral assessments follow the American Academy of Audiology (2010) guidelines75 which note that treatment for CAPD should be deficit-specific. There is an established body of evidence that CAPD can be ameliorated by remote microphone technology and/or auditory training, including some research with blinded, randomized controlled trials.12,24,28,39,79,81-83,90-101 Treatment can improve processing efficiency and listening. Improved listening can lead to better learning. Behavioral and electrophysiologic evidence demonstrates the effectiveness of both auditory training and/or remote microphone technology.79,80,84-86,97,102-113

5) Patients seek evaluation and treatment for CAPD. There is ample evidence to demonstrate that diagnosis of CAPD is sensitive and specific using available tests and procedures and that intervention for CAPD is efficacious. CAPD limits the ability to listen, read,32,98,106 communicate, and learn, and it adversely impacts the lives of special-needs children, veterans, seniors, and other patients who have TBI, cerebral vascular accidents, and other neuro-auditory disorders (eg, degenerative diseases) that underlie CAPD.

6) Audiologists support serving patients with CAPD. The advancement of science and debate among audiologists should not be misconstrued as justification to ignore our patients, or as a basis to label CAPD as “investigative.” While research will continue to improve diagnostic procedures and treatment approaches—as is true in all clinical fields—the current evidence base provides ample foundation to support audiologists who are dedicated to helping those with CAPD. CAPD is a valid clinical disorder, and providers such as insurers and schools should recognize the preponderance of evidence, as shown in this article, for supplying appropriate services to our patients.

As the experts in the diagnosis and treatment of  CAPD, audiologists are bound to follow their code of ethical practice by serving the patient population with CAPD. To deny patients appropriate evidence-based intervention for CAPD harms them. As a profession, we strive to obtain the highest level of evidence for CAPD identification and remediation. The references found in the online version of this article delineate a rich body of evidence supporting the validity and clinical utility of CAPD and current best practices that provide effective treatments which mitigate the impact of CAPD.

Correspondence can be addressed to Dr Abramson at: [email protected]

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Biography: Maria Abramson, AuD, has 30 years of experience in clinical practice with both adults and children and is the owner of Hear Now in Laguna Niguel, Calif; Deborah Moncrieff, PhD, is an Assistant Professor and Director of the Auditory Neurophysiology Laboratory at the University of Pittsburgh; Gail Chermak, PhD, is Professor of Audiology and Chair of the Department of Speech and Hearing Sciences, Elson S. Floyd College of Medicine, at Washington State University Health Sciences in Spokane, Wash; Frank Musiek, PhD, is a Professor in the Department of Speech, Language, Hearing Sciences at the University of Arizona; Donna Geffner, PhD, is dually certified and licensed as an audiologist and speech-language pathologist and maintains a private practice in Long Island, NY, and Lisa Guillory, AuD, is an audiologist at the Harry S. Truman Memorial Veterans’ Hospital in Columbia, Mo.

Original citation for this article: Abramson M, Moncrieff D, Chermak G, Musiek F, Geffner D, Guillory L. Six points of audiological consensus on central auditory processing disorders (CAPD). Hearing Review. 2018;25(4):38-40.

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