(31) P-MRS in migraine: fallen through the cracks

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

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.

Electrophysiological Characteristics of the Migraine Brain: Current Knowledge and Perspectives

BACKGROUND

Despite pain being its most prominent feature, migraine is primarily a disorder of sensory processing. Electrophysiology-based research in the field has consistently developed over the last fifty years.

OBJECTIVE

To summarize the current knowledge on the electrophysiological characteristics of the migraine brain, and discuss perspectives.

METHODS

We critically reviewed the literature on the topic to present and discuss articles selected on the basis of their significance and/or novelty.

RESULTS

Physiologic fluctuations within time, between-subject differences, and methodological issues account as major limitations of electrophysiological research in migraine. Nonetheless, several abnormalities revealed through different approaches have been described in the literature. Altogether, these results are compatible with an abnormal state of sensory processing.

PERSPECTIVES

The greatest contribution of electrophysiological testing in the future will most probably be the characterization of sub-groups of migraine patients sharing specific electrophysiological traits. This should serve as strategy towards personalized migraine treatment. Incorporation of novel methods of analysis would be worthwhile.

Familial history of migraine influences habituation of visual evoked potentials

Background

Lack of habituation of visual evoked potentials (VEP) is a common finding in migraine patients between attacks. Previous studies have suggested an electrophysiological familial aggregation pattern associated with migraine. The aim of this study was to evaluate the influence of a positive familial history of migraine on VEP amplitude and habituation.

Methods

We recorded six blocks of 100 VEP during continuous pattern-reversal stimulation in 30 patients with migraine between attacks (MO) and in 30 healthy volunteers, of whom 15 had a first-degree relative suffering from migraine (HVm) and 15 had not (HV).

Results

Both MO and HVm had a significant deficit of VEP habituation and similarly reduced N1-P1 first block amplitudes, compared to HV (habituation slope: MO = 0.033, HVm = 0.021, HV = −0.025, HV vs. MO p = 0.002, HV vs. HVm p = 0.036; mean N1-P1 amplitude in the first block: MO = 9.08 µV, HVm = 9.29 µV, HV = 12.19 µV. HV vs. MO p = 0.041, HV vs. HVm p = 0.076). The first block N1-P1 amplitude was negatively correlated with the habituation slope for both MO (ρ = −.44, p = 0.015) and HVm (ρ = −.56, p = 0.031) while no significant correlation was found in HV (ρ = .17, p = 0.53). There were no differences in VEP latencies between the groups.

Conclusions

Our study suggests that lack of habituation of visual evoked potentials is probably a genetically determined endophenotypic trait that is associated with both migraine and migraine susceptibility. We hypothesize that genetic diversity of populations could account for some of the discrepancies between electrophysiological studies performed in migraine and for interindividual variations among the subgroups.

Diagnosis, pathophysiology and management of chronic migraine: a proposal of the Belgian Headache Society

Chronic migraine (CM) is a disabling neurological condition affecting 0.5-2 % of the population. In the current third edition of the International Classification of Headache Disorders, medication overuse is no longer an exclusion criterion and CM is diagnosed in patients suffering from at least 15 headache days per month of which at least eight are related to migraine. CM is difficult to treat, and preventive treatment options are limited. We provide a pathogenetic model for CM, integrating the latest findings from neurophysiological and neuroimaging studies. On behalf of the Belgian Headache Society, we present a management algorithm for CM based on the international literature and adapted to the Belgian situation. Pharmacological treatment options are discussed, and recent data on transcranial and invasive neuromodulation studies in CM are reviewed. An integrated multimodal treatment programme may be beneficial to refractory patients, but at present, this approach is only supported by a limited number of observational studies and quite variable between centres.

Altered processing of sensory stimuli in patients with migraine

Migraine is a cyclic disorder, in which functional and morphological brain changes fluctuate over time, culminating periodically in an attack. In the migrainous brain, temporal processing of external stimuli and sequential recruitment of neuronal networks are often dysfunctional. These changes reflect complex CNS dysfunction patterns. Assessment of multimodal evoked potentials and nociceptive reflex responses can reveal altered patterns of the brain's electrophysiological activity, thereby aiding our understanding of the pathophysiology of migraine. In this Review, we summarize the most important findings on temporal processing of evoked and reflex responses in migraine. Considering these data, we propose that thalamocortical dysrhythmia may be responsible for the altered synchronicity in migraine. To test this hypothesis in future research, electrophysiological recordings should be combined with neuroimaging studies so that the temporal patterns of sensory processing in patients with migraine can be correlated with the accompanying anatomical and functional changes.