It is important to bear in mind that allodynia can refer either to pain
at a location other than the area where a nonpainful stimulus is applied,
or more commonly, dysesthetic pain resulting from a nonpainful stimulus.
- Problem: Physician asks whether patient ever feels pain in
an area other than the area being stimulated. Patient replies in the
negative.
Error: Patients with Central Pain have such poor localization
they often are unaware of this kind of allodynia. The proper technique
is to apply phasic stimulation (rub) various areas of the body against
something rough and ask the patient to pay attention to nearby areas
for any dysesthetic burning.
- Problem: Physician observes that patient looks normal and so
does not ask about allodynia.
Error: Patients put their best foot forward when dealing with
the medical profession. They often wear shoes or dress with more clothing
than usual ,with consequent agony, to avoid offending the physician
over a state of undress. The physician should ask the patient if the
touch of clothing causes burning. The physician should also note whether
the patient has left areas of the body uncovered with clothing.
- Problem: Physician tests for allodynia by touching the skin
with a cotton ball.
Error: Allodynia is dysesthetic, which means it displays "slow
summation". Time is required for its display. Slow summation occurs
much more rapidly with occlusive touch. Air circulation under
the cotton ball makes it unsuitable for testing allodynia. It is also
too gross to test subclinical loss of touch (von Frey hairs should be
used). The physician should lay a piece of newspaper on the patient's
body and wait for a minute or so before asking if the patient feels
pain.
- Problem: Physician tests for allodynia with an open safety
pin.
Error: Allodynia is pain from nonpainful stimulus. Pin prick
is normally (nociceptively) painful and cannot test allodynia. What
is being tested with pin prick is hyperpathia or overresponse to a painful
stimulus. In Central Pain, hyperpathia displays "delay with overshoot",
meaning there is a diminished response initially due to the sensory
loss, but as soon as the pain threshold is reached the response curve
is very, very steep, making pin prick testing a true torture. Patients
should not be tortured. Less sharp objects, such as a slightly blunted
pin, should be used to evaluate hyperpathia. Hyperpathia usually increase
proximally, the opposite of dysesthesia.
- Problem: Physician tests temperature sensibility with a cold
or hot test tube of water.
Error: This type of testing is too gross for Central Pain. The
patient has a greatly narrowed range of comfortable temperatures. It
is temperature change which most effectively initiates allodynia.
Proper testing involves determining how many degrees difference in two
test tubes (such as 4 degree. C) are required before a difference is
perceived by the patient, under circumstances of varied ambient temperature
at various reference points (e.g. sixty degrees F, seventy-two degrees
F, and ninety degrees F).
With time, the much narrowed thermal comfort range becomes reality to
the Central Pain patient, who no longer comments on their increased sensitivity
to temperature change nor their susceptibility to feeling pain from a
sudden temperature change which would not be painful to people without
Central Pain. Cold allodynia can be tested grossly by spraying room temperature
(68-74 degree F) water on the skin with a spray bottle and watching for
an overreaction, or questioning the patient about whether the spray was
perceived as shocking or painful. Alternatively, the clinician may ask
the patient whether a cold draft from a car air-conditioner causes burning
pain on the exposed part of the body.
For more information on allodynia, please read the
Allodynia web page.
