Clinical and electrophysiological responses to dietary challenge in migraineurs

Exploring sensory sensitivity, cortical excitability, and habituation in episodic migraine, as a function of age and disease severity, using the pattern-reversal task

BACKGROUND

Migraine is a cyclic, neurosensory disorder characterized by recurrent headaches and altered sensory processing. The latter is manifested in hypersensitivity to visual stimuli, measured with questionnaires and sensory thresholds, as well as in abnormal cortical excitability and a lack of habituation, assessed with visual evoked potentials elicited by pattern-reversal stimulation. Here, the goal was to determine whether factors such as age and/or disease severity may exert a modulatory influence on sensory sensitivity, cortical excitability, and habituation.

METHODS

Two similar experiments were carried out, the first comparing 24 young, episodic migraine patients and 28 healthy age- and gender-matched controls and the second 36 middle-aged, episodic migraine patients and 30 healthy age- and gender-matched controls. A neurologist confirmed the diagnoses. Migraine phases were obtained using eDiaries. Sensory sensitivity was assessed with the Sensory Perception Quotient and group comparisons were carried out. We obtained pattern-reversal visual evoked potentials and calculated the N1-P1 Peak-to-Peak amplitude. Two linear mixed-effects models were fitted to these data. The first model had Block (first block, last block) and Group (patients, controls) as fixed factors, whereas the second model had Trial (all trials) and Group as fixed factors. Participant was included as a random factor in both. N1-P1 first block amplitude was used to assess cortical excitability and habituation was defined as a decrease of N1-P1 amplitude across Blocks/Trials. Both experiments were performed interictally.

RESULTS

The final samples consisted of 18 patients with episodic migraine and 27 headache-free controls (first experiment) and 19 patients and 29 controls (second experiment). In both experiments, patients reported increased visual hypersensitivity on the Sensory Perception Quotient as compared to controls. Regarding N1-P1 peak-to-peak data, there was no main effect of Group, indicating no differences in cortical excitability between groups. Finally, significant main effects of both Block and Trial were found indicating habituation in both groups, regardless of age and headache frequency.

CONCLUSIONS

The results of this study yielded evidence for significant hypersensitivity in patients but no significant differences in either habituation or cortical excitability, as compared to headache-free controls. Although the alterations in patients may be less pronounced than originally anticipated they demonstrate the need for the definition and standardization of optimal methodological parameters.

Migraine Triggers and Oxidative Stress: A Narrative Review and Synthesis

BACKGROUND

Blau theorized that migraine triggers are exposures that in higher amounts would damage the brain. The recent discovery that the TRPA1 ion channel transduces oxidative stress and triggers neurogenic inflammation suggests that oxidative stress may be the common denominator underlying migraine triggers.

OBJECTIVE

The aim of this review is to present and discuss the available literature on the capacity of common migraine triggers to generate oxidative stress in the brain.

METHODS

A Medline search was conducted crossing the terms "oxidative stress" and "brain" with "alcohol," "dehydration," "water deprivation," "monosodium glutamate," "aspartame," "tyramine," "phenylethylamine," "dietary nitrates," "nitrosamines," "noise," "weather," "air pollutants," "hypoglycemia," "hypoxia," "infection," "estrogen," "circadian," "sleep deprivation," "information processing," "psychosocial stress," or "nitroglycerin and tolerance." "Flavonoids" was crossed with "prooxidant." The reference lists of the resulting articles were examined for further relevant studies. The focus was on empirical studies, in vitro and of animals, of individual triggers, indicating whether and/or by what mechanism they can generate oxidative stress.

RESULTS

In all cases except pericranial pain, common migraine triggers are capable of generating oxidative stress. Depending on the trigger, mechanisms include a high rate of energy production by the mitochondria, toxicity or altered membrane properties of the mitochondria, calcium overload and excitotoxicity, neuroinflammation and activation of microglia, and activation of neuronal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. For some triggers, oxidants also arise as a byproduct of monoamine oxidase or cytochrome P450 processing, or from uncoupling of nitric oxide synthase.

CONCLUSIONS

Oxidative stress is a plausible unifying principle behind the types of migraine triggers encountered in clinical practice. The possible implications for prevention and for understanding the nature of the migraine attack are discussed.

The brain is hyperexcitable in migraine

Migraine is a very common disorder occurring in 20% of women and 6% of men. Central neuronal hyperexcitability is proposed to be the putative basis for the physiological disturbances in migraine. Since there are no consistent structural disturbances in migraine, physiological and psychophysical studies have provided insight into the underlying mechanisms. This is a review of the neurophysiological studies which have provided an insight to migraine pathogenesis supporting the theory of hyperexcitability.

Asymmetric distribution of visual evoked potentials in patients with migraine with aura during the interictal phase

PURPOSE

One of the most commonly described electrocortical phenomena in patients with migraine is an increased interhemispheric asymmetry, in response to different sensory stimuli. This study aims to evaluate the bioelectrical activity of both occipital cortices in patients with migraine with visual aura (MA) during the interictal period, and its possible relationship with visual symptoms.

METHODS

The authors recorded visual evoked potentials (VEPs) simultaneously from the left (O1) and right (O2) occipital cortices (80% contrast 60', 30', 15', and 7.5' checkerboard stimuli reversed at 2 Hz) in 22 patients with MA and 20 control subjects. The main outcome measure was interhemispheric asymmetry (IA) for both implicit time and amplitude, defined as the difference between the left and right scalp derivation (in absolute values).

RESULTS

IA was significantly different in patients with MA with respect to controls when employing 60' (p<0.001) and 15' (p<0.05) checkerboard stimuli for implicit times, and 60' (p<0.05) checkerboard stimuli for amplitudes. On the other hand, IA was not statistically different (p>0.05) in patients with MA with respect to controls when employing 30' and 7.5' checkerboards for both implicit times and amplitudes, and 15' checkerboards for amplitudes. No correlations were found between IA and age, onset of disease, attack frequency, or side of headache/aura.

CONCLUSIONS

Patients with MA presented asymmetries in VEP responses not related to visual aura or to headache side during the pain-free phase. These abnormalities may be ascribed to abnormal visual information processing, resulting in a different cortical activation when both foveal and parafoveal stimuli are used.

Evaluation and proposal for optimalization of neurophysiological tests in migraine: part 1--electrophysiological tests

Neurophysiological testing has become a valuable tool for investigating brain excitability and nociceptive systems in headache disorders. Previous reviews have suggested that most neurophysiological tests have limited value for headache diagnosis, but a vast potential for exploring the pathophysiology of headaches, the central effects of certain pharmacological treatments and phenotype-genotype correlations. Many protocols, however, lack standardization. This meta-analytical review of neurophysiological methods in migraine was initiated by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9). Most of the neurophysiological approaches that have been used in headache patients are reviewed, i.e. evoked potentials, nociception-specific blink reflex, single-fibre electromyography, neuroimaging methods (functional MRI, PET, and voxel-based morphometry) and the nitroglycerin attack-provoking test. For each of them, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols. The first part is devoted to electrophysiological methods, the second to neuroimaging techniques and the NTG test.

Relationship between migraine and epilepsy in pediatric age

OBJECTIVE

Many studies have supported the hypothesis of alteration of cortical hyperexcitability as a possible pathological mechanism underlying the onset of migraine and epileptic attacks. Different biochemical pathways involving cellular structures may increase or decrease the excitability of neuronal membranes. The aim of this study was to identify a possible link between migraine and epilepsy from a clinical and neurophysiologic point of view.

METHODS

One-hundred thirty-seven children and adolescents consecutively diagnosed for tension-type headache and idiopathic migraine with and without aura were studied. Anamnestic, clinical, and instrumental data were collected by a neurological examination, a specific questionnaire, and awake electroencephalogram (EEG) registrations. EEG features of nonheadache and nonseizures control group were compared.

RESULTS

Fourteen cases (10.2%) had a positive history for seizures with fever, isolated seizures, or epilepsy. Distribution differed according to headache diagnosis; migraine with aura (MWA) was largely prevalent. Specific electroencephalographic abnormalities were present in 11.7% of the sample, with a significant different distribution across the groups of children with headache and the control group: specific interictal abnormalities were found in 10 of 23 (43.5%) children with MWA. Two factors, seizures and specific interictal electroencephalographic abnormalities, showed a different distribution in patients with MWA compared to other classes of headache and control group (P < or = .01).

CONCLUSION

The present study supports the hypothesis of a possible clinical continuum between some types of MWA and epileptic syndromes as entities due to altered neuronal excitability with similar genetic substrates.

Electrophysiological studies in migraine: a comprehensive review of their interest and limitations

Electrophysiological methods may help to unravel some of the pathophysiological mechanisms of migraine. Lack of habituation is the principal and most reproducible interictal abnormality in sensory processing in migraineurs. It is found in evoked potential (EP) studies for every stimulation modality including nociceptive stimuli, and it is likely to be responsible for the increased intensity dependence of EP. We have hypothesized that deficient EP habituation in migraine could be due to a reduced preactivation level of sensory cortices because of hypofunctioning subcortico-cortical aminergic pathways. This is not in keeping with simple hyperexcitability of the cortex, which has been suggested by some, but not all, studies of transcranial magnetic stimulation (TMS). A recent study of the effects of repetitive TMS on visual EP strongly supports the hypothesis that migraine is characterized by interictal cortical hypoexcitability. With regard to pain mechanisms in migraine, electrophysiological studies of trigeminal pathways using nociceptive blink and corneal reflexes have confirmed that sensitization of central trigeminal nociceptors occurs during migraine attacks.

Evoked potentials and transcranial magnetic stimulation in migraine: published data and viewpoint on their pathophysiologic significance

Migraine is a disorder in which central nervous sytem dysfunction might play a pivotal role. Electroneurophysiology seems thus particularly suited to study its pathophysiology. We have extensively reviewed evoked potential and transcranial magnetic stimulation studies performed in migraineurs in order to identify their pathophysiologic significance. Publications available to us were completed by a Medline search. Retrieved and personal data were compared with respect to methodology and interpreted according to present knowledge on cortical information processing. Results are in part contradictory which appears to be method-, patient- and disease- related. Nonetheless, both evoked potential and transcranial magnetic stimulation studies demonstrate that the cerebral cortex, and possibly subcortical structures, are dysfunctioning interictally in both migraine with and without aura. These electrophysiologic abnormalities tend to normalise just before and during an attack and some of them seem to have a clear familial and predisposing character. Besides the studies of magnetophosphenes which have yielded contrasting results, chiefly because the method is not sufficiently reliable, most recent electrophysiologic investigations of cortical activities in migraine favour deficient habituation and decreased preactivation cortical excitability as the predominant interictal dysfunctions. We propose that the former is a consequence of the latter and that it could favour both interictal cognitive disturbances as well as a cerebral metabolic disequilibrium that may play a role in migraine pathogenesis. To summarize, electrophysiologic studies demonstrate in migraine between attacks a cortical, and possibly subcortical, dysfunction of which the hallmark is deficient habituation.

The value of EEG in children with chronic headaches

To establish the usefulness of electroencephalography (EEG) as a diagnostic tool in the evaluation of headaches in children, we retrospectively reviewed the records of all children referred to our outpatient neuropediatric clinic because of recurrent headaches. Of 312 children, 257 (82%) underwent EEG tracings: 143 of the children who had had EEG recordings were diagnosed as migraineurs. In 31 (12%) of the children, the EEG revealed epileptic activity. The highest incidence of epileptic EEG activity was found amongst the children with very brief headaches. In 22 (8.6%) of the children, diffuse or focal slowing was detected. The group with migraine headache had a significantly higher incidence of slowing than the group with other types of headaches. There was no correlation between focal EEG abnormalities and brain radioimaging studies or clinical course. We conclude that despite the high incidence of epileptic abnormalities, the contribution of EEG to diagnosis and treatment in children with chronic headache is minimal, and should not be routinely prescribed in these children.