By Marcello Cherchi, MD PhD
Introduction
When a person develops a symptom (such as an unpleasant sensation, or a limitation of function), it is natural to ask, “What should I do to treat this symptom?” This is a reasonable question, but from a medical perspective, it is difficult (if not impossible) to answer because many (if not most) symptoms can be caused by more than one disease process. Consequently, a better initial question would be, “What disease is causing this symptom?”
An illustrative example is the symptom of, “stomachache.” Most people have experienced a stomachache, and thus can relate to this scenario. The list of diseases that can cause a stomachache is immense, ranging from the trivial (gas), through the treatable (appendicitis, bowel obstruction) to the lethal (pancreatic cancer), each of which has a different evolution, management strategies and prognosis. Consequently, the question, “What should I do to treat this stomachache?” is not actionable. The better question would be, “What disease is causing this stomachache?”
To approach an answer to the question, “What disease is causing the symptom of XXX?” a practitioner uses a variety of “tools.” The first is simply taking a good medical history of the illness. The second is a physical examination. After that, the diagnostic “tools” become more technological.
As in other fields of medicine, the diseases that fall within the purview of otoneurology and neuro-otology can have similar, or overlapping, clinical presentations and physical examination findings.
To some degree, progress in medicine has meant discovering ways of proving (or disproving) the presence of a disease process. If the diagnosis is already known, a test may be able to characterize or quantify it. Generally, tests (in a broad sense) can serve several purposes.
- Secure a diagnosis: Verify the presence (or absence) of a disease.
- Monitoring: For a disease that has already been identified, characterize or quantify its activity.
- Treatment decisions: In some cases, when a test result exceeds a particular threshold, a particular management strategy may be warranted.
Tests: audiologic and vestibular
In otoneurology and neuro-otology, clinically relevant quantitative tests became available in the early- and mid-20th century, including:
- Automated audiometry, sometimes called von Békésy audiometry (Békésy 1947).
- Caloric testing, systematized by Cawthorne, Fitzgerald and Hallpike (Cawthorne et al. 1942a, b; Fitzgerald and Hallpike 1942), drawing from observations originally made by Bárány (Bárány 1906b).
- Rotatory chair testing, based on observations originally made by Bárány (Bárány 1906a)
- Electronystagmography, based on the observations of Meyers (Meyers 1929) and Jacobson (Jacobson 1930).
While these were excellent tests, they comprised a relatively limited repertoire of tools. Beginning in the 1970s additional diagnostic techniques were developed, of which the main ones included:
- Otoacoustic emissions (OAEs), originally recognized by Kemp (Kemp 1978, 1979).
- Brainstem auditory evoked potentials (BAERs), originally described by Jewett and colleagues (Jewett et al. 1970).
- Head impulse testing (HIT), pioneered by Halmagyi and Curthoys (Halmagyi and Curthoys 1988).
- Vestibular evoked myogenic potentials (VEMPs). Early studies involved galvanic stimulation (Tokita et al. 1991), while later work used click- and tone burst stimuli (Colebatch et al. 1994a; Colebatch and Rothwell 1994; Colebatch et al. 1994b).
- Computerized dynamic posturography (CDP), based on the work of Louis Nashner (Nashner 1970, 1971), that he subsequently developed with other colleagues (Nashner et al. 1982).
Many other tests have also been explored, but either have remained restricted to research settings (such as scleral search coils), or have failed to demonstrate clinical utility.
Tests: imaging
Various imaging studies have played a role in otoneurology and neuro-otology. The most commonly used imaging study in the CT modality is the temporal bone CT. In the MRI modality, imaging of the brain (and internal auditory canals) and the cervical spinal cord, less commonly the thoracic and lumbosacral cord. In the ultrasound modality, Doppler imaging of the carotid and vertebral arteries is sometimes relevant.
The role of test results
Even the “tests” enumerated above still comprise a relatively limited repertoire. A person reading other pages on this website may notice that for many diseases, a fairly similar selection of tests may be relevant. This is not because one should “order every test in every patient.” Rather, it is because:
- Results from most tests are not binary; they usually present results along a spectrum.
- Every test in medicine has false positives (the test looks abnormal even though disease is absent) and false negatives (the test looks normal even though disease is present).
For many diseases, a series of tests will tend to exhibit a particular profile of results. The word “tend” is important, because biology is messy, and often a disease will not present with a perfect profile of test results. More commonly, a workup will reveal a set of results that more strongly (though not perfectly) supports one diagnosis over another. This is how test results can increase or decrease the suspicion for one or another diagnosis.
References
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Bárány R (1906b) Untersuchungen über den vom Vestibularapparat des Ohres reflektorisch ausgelösten rhythmischen Nystagmus und seine Begleiterscheinungen [Investigations on the rhythmic nystagmus triggered by the vestibular apparatus of the ear and its accompanying symptoms]. Monatschr Ohrenheilk 40: 193-297.
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