Part 1 – Central Auditory Evaluation in Private Practice: A Commentary with historical context and case observations.

Editor’s note: Dr. Ivey presents an historical as well as his clinical perspective on CAPD in practice. In over 40 years of academic as well as clinical experience Dr. Ivey has seen a wide variety of patients. In this issue of Pathways we have asked him to write a brief commentary on some of his more interesting encounters in the clinic.

 

by Robert G. Ivey, Ph.D., CCC-A

The central auditory test battery I use was developed at Colorado State University under the supervision of Jack Willeford, Ph.D. as my Master’s thesis completed in 1969.  While some would consider these tests to be somewhat dated they have served me well over many years in my practice.  They also provide an interesting slant on the history of diagnostic tests.  The battery I have often, though not exclusively used is briefly described as follows…..The contralateral competing sentences (CCS), filtered words (FW) and binaural resynthesis (BR—originally named binaural fusion).  These types of tests were chosen for the battery as a way to evaluate the central auditory nervous system in terms of levels and sidedness or laterality.  Is the lesion at the level of the brainstem (BR), cortex or corpus callosum and is it in the right or left side of the brain (FW, CCS) (as indicated by the literature at the time).  Words in ipsilateral competition (WIIC) was developed later at the University of Western Ontario.  This is a test of auditory tracking (commonly termed auditory figure-ground discrimination).  Auditory tracking (in brief) is a process by which we can follow one voice envelope and ignore other voices in the same auditory space.  It was thought that it tested neural substrate between the upper brainstem (binaural resynthesis) and the auditory cortex (filtered words—auditory closure) and can indicate laterality of the dysfunction.

Other measures that are often useful include:  the masking level difference (MLD) and or simultaneous binaural median plane lateralization (SBMPL) that evaluate the integrity of the fusion mechanism located at the lower brainstem.  The SBMPL is a test that presents a pulsed pure tone of the same frequency and phase to each ear simultaneously at a suprathreshold level.  Normal listeners will perceive at single midline auditory image of the tone.  Another test of the lower brainstem function (medial olivocochlear efferents) that I may use is the contralateral suppression of otoacoustic emissions (OAEs).

While I have not included measures such as dichotic digits, the Auditory Fusion Test-Revised or the GIN in the test battery that I use clinically on a routine basis, I will supplement the battery with these measures as necessary. I have also employed an array of auditory evoked potentials as will be discussed later in this commentary.

It is now well known that there are a significant number of children (and adults) who have difficulty hearing in complex listening environments that have normal hearing sensitivity.  These children in particular will be having difficulty hearing their teacher in the classroom.  The classroom is arguably the most important listening environment for children after having developed speech and language.  They will appear to have hearing, listening, attention, learning or behavior problems.  They may be blamed for “not listening” and told to “listen harder” or “pay attention.”  Therefore, increasing stress and anxiety for something that they have no control over.  They have no idea that how they hear in the classroom is any different than anyone else.  They may well develop behavioral problems and become less interested in school in general.  As a side note, over the years I also have received a significant number of referrals from pediatricians who were in the process of evaluating children for attentional deficits.

Many adults with central auditory deficits complain of difficulty in group and noisy environments such and restaurants or parties.  Many have always had difficulties in these environments (including classrooms when they were students) but never had an opportunity to be evaluated.  Other adults notice having greater difficulty in those environments and have been found to have central auditory lesions.  I felt it may be instructional to highlight a few cases of adults and children I have seen that present rather interesting histories and related circumstances that were evaluated with my rather “classic” central auditory test battery.

My earliest adult (38 year old male) central auditory patient was seen in Little Rock, Arkansas in the early 1970’s.  He had a history of weight loss and difficulty hearing.  He stated that if he was lying on his couch that if he was positioned such that his right ear was down that the noise the kids were making did not bother him.  Audiologic results showed normal hearing through 2000 Hz with a sharp drop in sensitivity in the higher frequencies bilaterally, consistent with noise exposure.  His SRTs were at 22 dBHL for both ears and word recognition was 90% bilaterally.  The first concern was the SBMPL (simultaneous binaural median plane lateralization) showed no clear midline perception at 1000 or 2000 Hz.  The ABLB (alternate binaural loudness balance) showed significant decruitment at 500 and 1000 Hz indicating neural involvement.  In this test the intensity of the questioned ear (the left) was set at 85 dBHL and loudness was matched with the right ear.  An abnormal difference of 25 to 30 dB was found for equal loudness. The judgement of loudness was definitely abnormal for the left ear.  Results for contralateral competing sentences (CCS) were 100% for the right ear and 96% for the left ear, and for binaural resynthesis (BR) 85% were within the range of normal.  Filtered words (500 Hz low-pass filtered monosyllable words—FW) showed scores of 70% for the right ear and well below normal at 42% for the left ear.  These results were interpreted to indicate a possible site of lesion to be at the right temporal lobe.  This was communicated to his neurologist who later found that this patient had cryptococcal meningitis in the right temporal lobe that was acquired through a fistula in the posterior of the right maxillary sinus as a result of chronic maxillary sinusitis.

Another patient (60 year old female) with a specific site of lesion complained that she could not understand what was being said in group situations particularly at parties.  She was found to have normal hearing through 4000 Hz for the right ear and through 2000 Hz for the left ear.  She had SRTs at 8 dBHL for both ears and word recognition of 98% for the right ear and 96% for the left ear.  Binaural resynthesis (500 Hz and 2000 Hz narrow-band-pass filtered spondees, each band-pass segment is presented simultaneously to opposite ears—BR) was found to normal at 85%.  Contralateral competing sentences (Paired sentences presented to the opposite ears at a signal to competition ratio of -15 dB—CCS) scores were 100% for the right ear and 70% for the left ear.  Filtered words showed scores of 60% for the right ear and 84% for the left ear.  The CCS results could point to a right-hemisphere lesion and/or a corpus callosum lesion while the filtered words result is more likely to point to a left temporal lobe lesion.  She reported that she had had a left deep parietal lobe tumor that had been removed.  This was consistent with a left hemisphere lesion with involvement of the corpus callosum. The FW test doesn’t require interhemispheric transfer but the (dichotic) competing sentences does hence the differing but accurate results on these two tests.  The BR was also accurate in that the patient had no brainstem involvement.

 

… To Be Continued…

 

About Pathways

Pathways is both a column that covers topics related to CAPD and Neuroaudiology and a society for people interested in central auditory disorders that regularly meets to discuss these issues.

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