Ben A J Mann
mann.ben at virgin.net
Sat Feb 10 18:53:43 EST 2001
Although this message was originally posted ages ago I thought that I'd put my two-penneth in.
In cases of NOHL cortical ERA is the gold standard, time consuming and thus costly.
ABR only gives threshold info for hearing in frequencies at and near 3 kHz, unless you use tone pips which are again time consuming, even with ABR we cannot guarantee the patient is hearing the stimulus if we get a good wave V, as there is the possibility of a central lesion.
Reflexes are useful but obviously a fairly small conductive element will obliterate the response and a small portion of the population with normal hearing doesn't have a reflex anyway. Reflexes only indicate a stimulus reaching as far as the superior olivery complex and a seventh cranial nerve lesion will also obliterate the response while the hearing may be retained (and even be hypersensitive).
Speech tests are useful in detecting the presence of an NOHL as the speech signal must reach the auditory cortex in order to be repeated. If they understand your instructions at normal levels but cannot repeat any speech material a NOHL can be suspected although not quantified, the same thing applies to inappropriate responses eg SHIP - "boat", MAN - "boy", or additionally in spondees only saying half of the spondee eg COWBOY - "boy".
Bekesy audiometry may show a type 5 pattern ie. pulsed tone below constant tone. Although few departments still have a Bekesy, and again it takes a while to do.
If you start with PTA and you are in a separate room to the patient, ensure that you have a talkback facility as the patient can create their own internal masking to give them a repeatable NOHL eg by humming during the test. You can also try the extended PTA method recently adapted and dexcribed by Lightfoot et al.
For unilateral losses look for no crossover of signal, particularly for unmasked bone conduction. You can also use the Stenger test using your audiometer to estimate to within around 10 dB what the actual HL is at each frequency without the patient realising you are doing anything different from conventional PTA.
OAE is nice and quick and easy, gives some indication of cochlea function in frequency bands, but is limited to cochlea function and the response is obliterated by a slight conductive element.
The yes-no test you described is a good one for kids (and even some adults) but of course is only useful if they are young (or nieve) enough to fall for it and again is qualitative rather than quantitative.
I cant remember what it's called or who first described this one but it works pretty well. Get the patient to tap out a rhythm. When they have got a good rhythm going play a different rhythm through the headphones at a level lower than their offered pure tone threshold. See how well they can keep up the original rhythm or if they start to follow the new one.
Adolescent girls are 3 times more likely to show a NOHL than boys.
Other things to consider with NOHL patients are their reasons for feigning the loss. I know of a little girl who gave a repeatable hearing loss very faithfully on repeated visits, she was confirmed NOHL by Bekesy audiometry (type 5). One day she offered normal PTA. Her mother said she was not surprised as her father had been sent to prison that week. Turns out that the child had been a victim of sexual abuse from her father. NOHL can be a cry for help, or a way for the NOHL patient to remove themselves from a hostile environment even if it in the very short term.
You've probably found out most of these already by now, and I'm sure that I've missed a few useful tests, but hopefully this is useful for someone.
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