Central Auditory Processing Disorder (CAPD)

CAPD, a distinct and defined diagnosis (ICD-10CM Code: H93.25), refers to deficits in the processing of information in the central auditory nervous system (CANS). CAPD is an umbrella term that covers a variety of difficulties in processing auditory input due to the interactions of the auditory periphery and the CANS. After sound is decoded in the cochlea or inner ear, it travels via the VIIIth cranial nerve to the brainstem and ultimately to higher areas of the brain. There are a number of relay points along the pathway that contribute to the complex neural activities of decoding, analysis along frequency, intensity and time domains, distribution, and interpretation of the incoming auditory signal. Current research has been directed at determining the likely, abnormal neural activity that may underlie deviations in auditory perception, as well as methods and strategies for remediation of these conditions.

CAPD is a condition found in children and adults that typically presents with normal hearing. The classic, direct symptoms of CAPD involve difficulty recognizing speech in the presence of background noise or other competing signals, and difficulty recognizing rapidly presented speech. Associated difficulties (e.g., ADHD, dyslexia, language impairment) can lead to additional symptoms including: resistance to remediation for reading deficits and other auditory-based learning, difficulty listening in quiet, difficulty following simple or complex auditory directions, difficulty maintaining auditory attention and frequent requests for repetitions. 

Behavioral central auditory tests and electrophysiological procedures reveal deficits in specific neurobiological activities underlying auditory processing dysfunction. Following the basic audiological evaluation that establishes hearing sensitivity, an audiologist then determines which specific auditory process to examine. These processes include: auditory discrimination, temporal resolution, temporal sequencing of pitch patterns, binaural integration, binaural separation, auditory figure ground (i.e., auditory closure), neural synchronization and related functions.

In order to evaluate these process areas, a test battery approach is thought to be more effective, since one test is not likely to maximize the accuracy of differential diagnosis and management considering the heterogeneity of CAPD. In fact, due to the complexity of the peripheral and central auditory system, and their interdependency, it is necessary to have a battery of deficit-specific CAPD tests that are implemented based on patient complaints and behavioral observation. Data continues to be accumulated that demonstrate the validity of central auditory test procedures that are based on confirmed disorders of individuals with neurologically auditory based lesions. Behavioral CAPD test batteries, with high sensitivity and specificity, as well as electrophysiological procedures, have been evolving over several decades. The design of these test batteries is primarily to identify selected deficits tied to the CANS for which specific remediation can be provided. The tests used are evidenced-based and employ simple speech and tonal stimuli. While specific tests may vary, the assessment of the auditory processes themselves are evaluated based upon the specific, unique needs of the patient, the case history, multidisciplinary input, and the audiologist’s expertise.

CAPD assessment typically results in appropriate diagnoses of the specific auditory process or processes that are deficient. Only the expertise of the audiologist’s CAPD evaluation can determine the individual’s specific deficit profile and which deficit-specific interventions are indicated. Audiologists’ test batteries account for neural maturation of the child, and for cognitive and language variables. CAPD assessment and treatment is in an audiologist’s scope of practice, and they typically work with their peers including speech-language pathologists, educational specialists, occupational therapists and others to provide the comprehensive care that is indicated.  Only audiologists who have undergone extensive training in this professional area should undertake the evaluation and diagnosis of CAPD.

In terms of remediation, based on the notion that understanding targeted CANS dysfunction and the associated auditory-based behavioral deficits, a number of evidence-based strategies and therapies have been developed that have led to effective remediation of a number of functional deficits manifested in individuals diagnosed with specific processing deficits associated with CAPD. 

In summary, significant strides have been made in understanding the central auditory nervous system, as well as a number of the neurobiological underpinnings of CAPD in both children and adults. The investigation of CAPD is an evolving aspect of the profession of Audiology with a growing body of evidence, from several disciplines including audiology, speech-language pathology, auditory neuroscience and others, that the successful diagnosis and treatment of specific deficits of CAPD are achievable.  In terms of diagnosis, a test battery approach, using behavioral tests with high sensitivity and specificity, and possibly electrophysiological tests as well, are favored.  In addition, it should be appreciated that CAPD may occur with concomitant neurologically-based auditory deficits and/or deficits in language learning and cognition. In conclusion, it is essential that remediation of aspects of CAPD be prescribed by the audiologist, based upon assessment and tailored to the specific deficits demonstrated, as well as the learning and language needs of a given individual. Audiologists often call upon support from speech language pathologists, educational specialists, occupational therapists, and other professionals in the management of CAPD in children. Patients with CAPD can be helped by the strides made in identification and treatment of CAPD.