Olfactory hypersensitivity (OHS) may occur during
migraine attacks and seems to be very specific to this form of
headache. OHS is also observed during migraine-free periods and is associated with the presence of odour-triggered attacks. Yet the
pathophysiology of OHS remains unknown. The aim of our study was to evaluate
olfactory processing in migraineurs with OHS and to investigate whether regional
cerebral blood flow (rCBF) associated with
olfactory stimulation is modified in these patients compared with controls. Eleven migraineurs with OHS and 12 controls participated in a H(2) (15)O-positron emission
tomography study, including three scans in which
odours were delivered and three scans where only odourless air was delivered. rCBF during
olfactory condition was compared with that for the odourless baseline condition. Between-group analyses were performed using voxel-based and region-of-interest analyses. During both
olfactory and non-olfactory conditions, we observed higher rCBF in the left
piriform cortex and antero-superior
temporal gyrus in migraineurs compared with controls. During
odour stimulation, migraineurs also showed significantly higher
activation than controls in the left
temporal pole and significantly lower
activation in the frontal (left
inferior as well as left and right middle frontal
gyri) and temporo-parietal (left and right
angular, and right
posterior superior
temporal gyri) regions,
posterior cingulate gyrus and right
locus coeruleus. These results could reflect a particular role of both the
piriform cortex and antero-superior
temporal gyrus in OHS and odour-triggered
migraine. Whether these rCBF changes are the cause or a consequence of odour-triggered
migraines and
interictal OHS remains unknown. Further comparisons between migraineurs with and without OHS are warranted to address this issue. The abnormal cerebral
activation patterns during
olfactory stimulation might reflect altered
cerebrovascular response to
olfactory stimulation due to the
migraine disease, or an abnormal
top-down regulation process related to OHS.
