Monday, March 27, 2017

Your Audiology Tutorial: Tuning Fork Tests

That steel, two-pronged fork that you may have seen in your ear,  nose, and throat doctor's office is used for some pretty quick and efficient diagnostic tests.  In other contexts, of course,  it may be used to tune musical instruments.  Tuning fork tests can be used to determine if a patient's hearing loss -if in fact there is one- is conductive (middle ear: eardrum, Eustachian tube) or sensorineural (inner ear: cochlea, cranial nerve).  In many ENT clinics, a 512 Hz fork is utilized.

There are four type of tuning fork tests, each named after a German otologist:

1. Weber:  After lightly striking fork against hand, the examiner places the stem on patient's forehead. The patient is asked if the resulting tone lateralizes to either ear (is heard louder in one or the other). If heard equally loud in both ears, the test is considered negative for hearing loss.  If the tone is heard in the ear reported to be worse, the loss may be conductive. If heard in the better ear, sensorineural.

2. Rinne: Patient is asked to put finger in the opposite of the ear being tested.  Stem of fork is struck by examiner and first placed on mastoid bone (just behind your pinna, or outer ear).  The patient is asked to respond when he or she no longer hears tone.  The stem is then placed in front of, but not touching the outer ear. The patient is asked to report if the tone was heard longer/louder.  If so, this can indicate a conductive hearing loss.  If heard louder on the mastoid, the loss may be sensorineural.

The following tests are less commonly performed:

3. Schwabach: Stem of fork is placed on patient's mastoid, then examiner's, alternated until one of them no longer perceives the tone. If patient hears tone longer than examiner, it may be conductive. If patient hears tone for shorter time, it may be sensorineural.

4. Bing: Stem is placed on mastoid while patient inserts and removes finger at entrance of ear canal.  If patient reports that sound alternated in intensity with finger in and out, loss may be sensorineural; if no change, conductive.

You can imagine that there are several confounding factors to these tests.  Certainly the patient's lack of understanding of procedure and the examiner's possibly sloppy technique (especially during the Schwabach) should be considered.  What if the examiner has a hearing loss?

Audiologists don't usually do tuning fork tests, as testing air and bone conduction (with different transducers) with an audiometer will confirm the nature of the hearing loss.

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