Abstract
In some patients, migraine attacks are associated with symptoms of allodynia which can be localized (cephalic) or generalized (extracephalic). Using functional neuroimaging and cutaneous thermal stimulation, we aimed to investigate the differences in brain activation of patients with episodic migraine (n = 19) based on their allodynic status defined by changes between ictal and interictal pain tolerance threshold for each subject at the time of imaging. In this prospective imaging study, differences were found in brain activity between the ictal and interictal visits in the brainstem/pons, thalamus, insula, cerebellum and cingulate cortex. Significant differences were also observed in the pattern of activation along the trigeminal pathway to noxious heat stimuli in no allodynia vs. generalized allodynia in the thalamus and the trigeminal nucleus but there were no activation differences in the trigeminal ganglion. The functional magnetic resonance imaging (fMRI) findings provide direct evidence for the view that in migraine patients who are allodynic during the ictal phase of their attacks, the spinal trigeminal nucleus and posterior thalamus become hyper-responsive (sensitized)–to the extent that they mediate cephalic and extracephalic allodynia, respectively. In addition, descending analgesic systems seem as “switched off” in generalized allodynia.
Highlights
During a migraine attack, most patients develop cutaneous allodynia, defined as pain perception evoked by normally non-noxious stimuli [1, 2]
We focused on two questions: (1) Are there any differences in response to noxious thermal stimulation in the migraine brain between ictal vs. interictal states along the trigeminovascular pathway using functional magnetic resonance imaging?; and (2) How are the brain response changes manifested in the generalized allodynic state different from those in the non-allodynic state? The observations and insights gathered from the brain changes in allodynia may help understand if the progression from no allodynia to generalized allodynia engages brain areas involved in the sensory, emotional and other aspects of migraine and how each is involved
Six patients were excluded from the analysis due to the long time separation between the interictal scan and the scan obtained during the migraine attack (> 1 year)
Summary
Most patients develop cutaneous allodynia, defined as pain perception evoked by normally non-noxious stimuli [1, 2]. Patients with migraine may experience pain from common daily activities, such as wearing glasses, or taking a shower [2, 3]. The pain in migraine is thought to contain an early activation and sensitization of first-order.
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