Editor’s note: In response to our recent School Matters column, “Don’t Wait to Diagnose Auditory Processing Disorder,” we are presenting a series of blog posts sharing various views on the validity of APD as a specific diagnosis.
A legitimate communications disorder is called a “clinical entity.” The concept of the clinical entity is important when addressing controversial conditions such as auditory processing disorder (APD)—sometimes also called central auditory processing disorder. Although the ASHA Working Group on APD concluded in 2005 that sufficient evidence exists to support APD as a diagnostic entity, others—me included—remain skeptical.
In his 2011 article published in Language, Speech, and Hearing Services in Schools (LSHSS), Alan G. Kamhi wrote that there are, “compelling theoretical and clinical reasons to question whether APD is in fact a distinct clinical entity.” Other communication sciences and disorders professionals agree with Kamhi’s take on APD, including Geraldine Wallach in an article from the same issue of LSHSS. She notes: “Professionals are hard pressed, even if they accept the APD diagnosis, to find agreement about how to proceed to help the children and adolescents in their care.”
“The evidence base is too small and weak to provide clear guidance to speech-language pathologists faced with treating children with diagnosed APD,” concludes a review from the ASHA Committee on the Role of the Speech-Language Pathologist in Identifying and Treating Children with APD.
These viewpoints lead me to pose a question: “How do we determine if a condition is a legitimate disorder deserving of specific diagnoses and treatment?”
In 1677, Thomas Sydenham—known as a founder of clinical medicine—wrote in the preface to his Observationes Medicae, “Nature, in the production of disease, is uniform and consistent; so much so, that for the same disease in different persons the symptoms are for the most part the same.”
Homogeneity is a hallmark of Sydenham’s description of disease. Using Sydenham’s description of disease, along with the 1949 writings of physician Otto Ernst Guttentag, I construed four criteria on how to identify a clinical entity: It 1) possesses an unambiguous definition, 2) represents a homogeneous patient group, 3) represents a limitation for the patient, and 4) facilitates diagnosis and intervention.
When applying these criteria to APD, the disorder doesn’t hold-up as a legitimate clinical entity. First, APD does not possess an unambiguous definition. James Jerger—founding president of the American Academy of Audiology—said: “There are more definitions of APD than there are children who have the disorder.” Second, APD does not represent a homogeneous patient group. Audiologists and SLPs use a battery of tests—chosen from a number of available behavioral assessments—for diagnoses. The wide variety of test content results in a clearly heterogeneous patient group. Varied definitions of APD, plus the lack of test standardization, makes it unclear if an APD diagnosis meets the third criteria—a limitation for the patient. As for the fourth criteria, the construct of APD does not facilitate (or make easy) the process of diagnosis or intervention.
Based on the Sydenham-Guttentag criteria for the clinical entity, APD is not a legitimate disorder. However, a number of listening deficits currently associated with APD may meet these criteria. For example, a speech recognition in noise disorder qualifies as clinical entity. Other potential clinical entities include amblyaudia, a spatialized listening in noise disorder and a temporal resolution disorder. These diagnoses are consistent with a proposed alternative procedure to the APD construct that moves away from testing “auditory processing” and toward identifying and supporting clients with listening challenges. By focusing our efforts on clearly defined clinical entities, we can better serve our patients.
Andrew Vermiglio, AuD, CCC-A, is the director of the Speech Perception Lab at East Carolina University. He also helped with the development of the Source Azimuth Identification in Noise Test (SAINT) and a number of commercial versions of the Hearing in Noise Test (HINT).firstname.lastname@example.org