Evidence of an increased neuronal activation-to-resting glucose uptake ratio in the visual cortex of migraine patients: a study comparing 18FDG-PET and visual evoked potentials

Abstract

Background: Migraine attacks might be triggered by a disruption of cerebral homeostasis. During the interictal period migraine patients are characterized by abnormal sensory information processing, but this functional abnormality may not be sufficient to disrupt the physiological equilibrium of the cortex unless it is accompanied by additional pathological mechanisms, like a reduction in energetic reserves. The aim of this study was to compare resting cerebral glucose uptake (using positron emission tomography (¹⁸fluorodeoxyglucose-PET)), and visual cortex activation (using visual evoked potentials (VEP)), between episodic migraine without aura patients in the interictal period and healthy volunteers.

Methods: Twenty episodic migraine without aura patients and twenty healthy volunteers were studied. ¹⁸FDG-PET and VEP recordings were performed on separate days. The overall glucose uptake in the visual cortex-to-VEP response ratio was calculated and compared between the groups. Additionally, PET scan comparisons adding area under the VEP curve as a covariate were performed. For case-wise analysis, eigenvalues from a specific region exhibiting significantly different FDG-PET signal in the visual cortex were extracted. Standardized glucose uptake values from this region and VEP values from each subject were then coupled and compared between the groups.

Results: The mean area under the curve of VEP was greater in migraine patients compared to healthy controls. In the same line, patients had an increased neuronal activation-to-resting glucose uptake ratio in the visual cortex. Statistical parametric mapping analysis revealed that cortical FDG-PET signal in relation to VEP area under the curve was significantly reduced in migraineurs in a cluster extending throughout the left visual cortex, from Brodmann's areas 19 and 18 to area 7. Within this region, case-wise analyses showed that a visual neuronal activation exceeding glucose uptake was present in 90% of migraine patients, but in only 15% of healthy volunteers.

Conclusion: This study identifies an area of increased neuronal activation-to-resting glucose uptake ratio in the visual cortex of migraine patients between attacks. Such observation supports the concept that an activity-induced rupture of cerebral metabolic homeostasis may be a cornerstone of migraine pathophysiology. This article has been selected as the winner of the 2018 Enrico Greppi Award. The Enrico Greppi Award is made to an unpublished paper dealing with clinical, epidemiological, genetic, pathophysiological or therapeutic aspects of headache. Italian Society for the Study of Headaches (SISC) sponsors this award, and the award is supported through an educational grant from Teva Neuroscience. This article did not undergo the standard peer review process for The Journal of Headache and Pain. The members of the 2018 Enrico Greppi Award Selection Committee were: Francesco Pierelli, Paolo Martelletti, Lyn Griffiths, Simona Sacco, Andreas Straube and Cenk Ayata.

Keywords: Astrocytes; Cerebral energy metabolism; Headache; Neurophysiology.

Fig. 1

Mean Visual Evoked potentials (x = time in ms, y = trial number, z = amplitude in μV) in healthy volunteers (left) and episodic migraine patients (right). The area under the curve was calculated with respect to the baseline (zero)

Fig. 2

Areas of increased metabolism in healthy controls compared with migraine patients using the interaction with area under the VEP as regressor. Clockwise from top left: (a) coronal view, (b) sagittal view, (c) axial view, and (d) “glass brain” representation and design matrix

Fig. 3

Left: Metabolic and Visual Z-scores of each participant plotted on a Cartesian coordinates plane. Points above the dashed diagonal line (light blue shaded area) correspond to participants with higher glucose uptake in the visual cortex with respect to their visual responsiveness score. Points below the dashed diagonal line (light red shaded area) correspond to participants exhibiting disproportionally higher visual responses considering their glucose uptake. Right: relative proportion of subjects of each within each side of the dashed diagonal line of the Cartesian plot. The asterisks (***) indicate a p value < 0.001

Fig. 4

Schematic representation of astrocytic (purple) and neuronal (yellow) metabolism at rest (a, left) and upon stimulation (b, right). Only astrocytes accumulate glucose (green) at rest, whereas upon stimulation, energetic reserves are degraded in order to provide energy substrates (lactate, orange) to neurons. Astrocytes in exchange reuptake exceeding glutamate at the synaptic cleft level (not shown). For details see ref. [42]