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Since the Nobel prize-winning work of B醨醤y early last century, caloric testing has been the mainstay
of vestibular assessment. Only relatively recently have other tests of vestibular function become
available and these are often confined to specialist units. The caloric stimulation of the vestibular system
and the resulting ENG/VNG tests have become relied upon to determine the presence of a vestibular
lesion, but it is becoming more and more apparent that a caloric tests can be normal in a wide range of
vestibular lesions. One of the most important principles in the theory that underlies this is that fact that
the vestibular system must function in a different way at varying head velocities to produce a gain of 1.0
to prevent oscillopsia through the vestibulo-ocular reflex (VOR).
Magnetic scleral search coil (MSSC) measurement of eye movement during head perturbations
of increasing velocities show that there can be a difference in gain depending on the velocity of the
head; it is possible to have a normal gain with low angular velocities, but have a very diminished gain
at higher velocities. Of 168 patients, attending a tertiary balance unit, sent for caloric testing, 68 had
normal results;. MSSC testing was positive in 32 patients. Although low velocity gains were normal,
high velocity gains for the left and right ears were 0.84(SD=0.15) and 0.78(SD=0.14) respectively, well
below normal. Clinical evaluation of the 32 patients showed a positive head thrust test or reduced DVA
in 30 patients; showing that the abnormality was clinically detectable in 30/32 patients.
Other anomalies suggest that using caloric testing as a screening test may be problematic.
Asymmetries in Jonkee?s formula when temperatures below 30癈 are used against warm calorics
suggest that the arbitrary nature of the 30/44癈 separation cannot be relied upon. Thermodynamic
and conceptual problems with caloric/ENG/VNG testing are discussed in greater detail in this lecture.
Biography
Dr Pothier attended medical school at the University of Cape Town, South Africa. He then undertook his Otolaryn
-
gology training in London and the South West of England. Fellowship trained in Neurotology in Toronto, Canada where
he now works as an Otologist/Neurotologist with an interest in middle ear and vestibular disorders, as well as Health
Informatics. He has a primary research interest in bilateral vestibular loss. He has published over 80 peer-reviewed
articles and has a Bacon number of 4.
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