Brain, Vol 121, Issue 2 345-356, Copyright © 1998 by Oxford University Press
R Peyron, L Garcia-Larrea, MC Gregoire, P Convers, F Lavenne, L Veyre, JC Froment, F Mauguiere, D Michel and B Laurent
We used PET to study regional cerebral blood flow (rCBF) changes in nine
patients with unilateral central pain after a lateral medullary infarct
(Wallenberg's syndrome). All patients presented, on the abnormal side, a
combination of hypaesthesia to noxious and thermal stimuli and allodynia to
rubbing of the skin with a cold object (i.e. abnormal pain to innocuous
stimulation). The rCBF responses during allodynia were compared with those
obtained during stimulation of the normal side using (i) a cold non-noxious
stimulus identical to that applied to the painful side, and (ii) an
electrical high-frequency stimulus at painful ranges. Statistical analysis
disclosed two abnormal patterns of rCBF change during allodynia. First,
there is a quantitative change whereby the blood flow response was out of
proportion with the actual intensity of the stimulus, i.e. the pattern of
activation by innocuous rubbing of the skin was in our patients identical
to that previously reported in response to painful stimuli in normal
subjects. This pattern concerned primarily the contralateral thalamus in
its lateral half and the primary and somatosensory areas, as well as
inferior parietal [Brodmann area (BA) 39/40], anterior insular (BA 6) and
medial prefrontal (BA 10) cortices. Thalamic over- activity may reflect
abnormal transduction and amplification of sensory inputs after
spinothalamic deafferentation. This might be responsible for both increased
rCBF in multiple cortical targets and the perceived shift of stimulus
intensity from innocuous to painful ranges. The second abnormality
associated with allodynic sensation was qualitative. It concerned
exclusively the contralateral cingulate gyrus, which did not exhibit the
usual pain-related rCBF increase reported in normal subjects. This abnormal
cingulate response may account for the peculiar response of lateral
medullary infarct patients to allodynic pain, which is not simply perceived
as an exaggerated pain sensation, but as a new, strange and extremely
unpleasant feeling, not previously experienced by the patients.
ARTICLES
Allodynia after lateral-medullary (Wallenberg) infarct. A PET study
Neurological Department, Bellevue Hospital, Saint-Etienne, France.
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