Beta-blocker migraine prophylaxis affects the excitability of the visual cortex as revealed by transcranial magnetic stimulation

EEG Changes in Migraine-Can EEG Help to Monitor Attack Susceptibility?

Migraine is a highly prevalent brain condition with paroxysmal changes in brain excitability believed to contribute to the initiation of an attack. The attacks and their unpredictability have a major impact on the lives of patients. Clinical management is hampered by a lack of reliable predictors for upcoming attacks, which may help in understanding pathophysiological mechanisms to identify new treatment targets that may be positioned between the acute and preventive possibilities that are currently available. So far, a large range of studies using conventional hospital-based EEG recordings have provided contradictory results, with indications of both cortical hyper- as well as hypo-excitability. These heterogeneous findings may largely be because most studies were cross-sectional in design, providing only a snapshot in time of a patient's brain state without capturing day-to-day fluctuations. The scope of this narrative review is to (i) reflect on current knowledge on EEG changes in the context of migraine, the attack cycle, and underlying pathophysiology; (ii) consider the effects of migraine treatment on EEG features; (iii) outline challenges and opportunities in using EEG for monitoring attack susceptibility; and (iv) discuss future applications of EEG in home-based settings.

Interictal Dysfunctions of Attention, Vigilance, and Executive Functions in Migraine and Their Reversal by Preventive Treatment: A longitudinal Controlled Study

OBJECTIVE

To assess attention, vigilance, and executive functions in migraine patients during headache-free (interictal) periods and in healthy controls without migraine and to study the impact of migraine preventive treatment on these cognitive functions.

METHODS

Preventive drug-naive migraine patients, aged ≥18 years, without a history of medication overuse were studied and compared to non-migraine controls. Psychiatric comorbidity was screened by Patient Health Questionnaire-9, and those who screened positive were evaluated further by specific scales. The Epworth Sleepiness Scale assessed subjective complaints of sleep quality. Cognitive functions were assessed by Mini-Mental State Examination (MMSE), digit span forward and backward (DS-F, DS-B), trail-making tests (TMT-A and B) and Stroop word (SW), Stroop color (SC), and Stroop interference (SI) tests. Cognitive test scores at the end of 6 months following treatment were compared to baseline scores.

RESULTS

One hundred and fifty migraine patients and controls each were studied. Compared to controls, migraine patients performed significantly worse in DS-B ( P < 0.0001), TMT-A ( P = 0.00004), TMT-B ( P < 0.0001), SW ( P < 0.0001), SC ( P < 0.0001), and SI ( P = 0.0221). MMSE scores did not differ between patients and the controls ( P = 0.3224). Compared to the patients without psychiatric comorbidity, migraine patients with psychiatric comorbidity showed no significant differences in the cognitive test scores. Significant improvement in all cognitive test scores ( P < 0.001) was observed after 6 months of treatment.

CONCLUSION

Migraine patients, compared to non-migraine controls, showed deficits in attention, vigilance, and executive functions during the interictal period, which improved with successful preventive treatment. Psychiatric comorbidities did not have a significant impact on cognitive dysfunctions.

A critical review of the neurovascular nature of migraine and the main mechanisms of action of prophylactic antimigraine medications

INTRODUCTION

Migraine involves neurovascular, functional, and anatomical alterations. Migraineurs experience an intense unilateral and pulsatile headache frequently accompanied with vomiting, nausea, photophobia, etc. Although there is no ideal preventive medication, frequency in migraine days may be partially decreased by some prophylactics, including antihypertensives, antidepressants, antiepileptics, and CGRPergic inhibitors. However, the mechanisms of action involved in antimigraine prophylaxis remain elusive.

AREAS COVERED

This review recaps some of the main neurovascular phenomena related to migraine and currently available preventive medications. Moreover, it discusses the major mechanisms of action of the recommended prophylactic medications.

EXPERT OPINION

In the last three years, migraine prophylaxis has evolved from nonspecific to specific antimigraine treatments. Overall, nonspecific treatments  mainly involve neural actions, whereas specific pharmacotherapy (represented by CGRP receptor antagonists and CGRPergic monoclonal antibodies) is predominantly mediated by neurovascular mechanisms that may include, among others: (i) reduction in the cortical spreading depression (CSD)-associated events; (ii) inhibition of pain sensitization; (iii) blockade of neurogenic inflammation; and/or (iv) increase in cranial vascular tone. Accordingly, the novel antimigraine prophylaxis promises to be more effective, devoid of significant adverse effects (unlike nonspecific treatments), and more beneficial for the quality of life of migraineurs.

The visual system as target of non-invasive brain stimulation for migraine treatment: Current insights and future challenges

The visual network is crucially implicated in the pathophysiology of migraine. Several lines of evidence indicate that migraine is characterized by an altered visual cortex excitability both during and between attacks. Visual symptoms, the most common clinical manifestation of migraine aura, are likely the result of cortical spreading depression originating from the extrastriate area V3A. Photophobia, a clinical hallmark of migraine, is linked to an abnormal sensory processing of the thalamus which is converged with the non-image forming visual pathway. Finally, visual snow is an increasingly recognized persistent visual phenomenon in migraine, possibly caused by increased perception of subthreshold visual stimuli. Emerging research in non-invasive brain stimulation (NIBS) has vastly developed into a diversity of areas with promising potential. One of its clinical applications is the single-pulse transcranial magnetic stimulation (sTMS) applied over the occipital cortex which has been approved for treating migraine with aura, albeit limited evidence. Studies have also investigated other NIBS techniques, such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), for migraine prophylaxis but with conflicting results. As a dynamic brain disorder with widespread pathophysiology, targeting migraine with NIBS is challenging. Furthermore, unlike the motor cortex, evidence suggests that the visual cortex may be less plastic. Controversy exists as to whether the same fundamental principles of NIBS, based mainly on findings in the motor cortex, can be applied to the visual cortex. This review aims to explore existing literature surrounding NIBS studies on the visual system of migraine. We will first provide an overview highlighting the direct implication of the visual network in migraine. Next, we will focus on the rationale behind using NIBS for migraine treatment, including its effects on the visual cortex, and the shortcomings of currently available evidence. Finally, we propose a broader perspective of how novel approaches, the concept of brain networks and the integration of multimodal imaging with computational modeling, can help refine current NIBS methods, with the ultimate goal of optimizing a more individualized treatment for migraine.

Gray matter volume modifications in migraine

Objective

To explore cross-sectional and longitudinal gray matter (GM) volume changes in patients with migraine and their association with patients' clinical characteristics and disease activity.

Methods

Brain T2-weighted and 3-dimensional T1-weighted scans were acquired from 73 episodic migraineurs and 46 age- and sex-matched nonmigraine controls at baseline. Twenty-four migraineurs and 25 controls agreed to be reexamined after a mean follow-up of 4 years. Using a general linear model and SPM12, a whole-brain analysis was performed to assess GM volume modifications.

Results

At baseline, compared to controls, patients with migraine showed lower cerebellar GM volume and higher volume of regions of the frontotemporal lobes. At follow-up, migraineurs were significantly older than controls. Over the follow-up, migraineurs developed an increased volume of frontotemporoparietal regions, which was more prominent in patients with a higher baseline disease activity: long disease duration and high attack frequency. Migraineurs also developed decreased GM volume of visual areas, which was related to higher pain severity. Patients with an increased attack frequency at follow-up experienced both increased and decreased volume of nociceptive regions. In migraineurs, reduced GM volume of extrastriate visual areas during the follow-up was significantly correlated to baseline disease activity: shorter disease duration and lower attack frequency.

Conclusion

In this cohort, the migraine brain changes dynamically over time, and different pathophysiologic mechanisms can occur in response to patients' disease severity. The interaction between predisposing brain traits and experience-dependent responses might vary across different nociceptive and visual areas, thus leading to distinct patterns of longitudinal GM volume changes.

Preventive drugs restore visual evoked habituation and attention in migraineurs

Visual system pathway dysfunction has been postulated in migraineurs. We wanted to investigate if any difference exists interictally in visual attention and visual evoked habituation of frequently attacked migraineurs compared to the healthy control group. The effects of 3-month prophylactic migraine treatment on these parameters were also assessed. The migraineurs at headache-free interval (n = 52) and age, sex-matched healthy controls (n = 35) were compared by habituation response to 10 blocks of repetitive pattern-reversal visual stimuli (each block consisted 100 responses). The amplitude changes of 5th and 10th blocks were further compared with that of block 1 to assess the response of habituation (i.e., decrease) or potentiation (i.e., increase). The level of sustained visual attention was assessed by Cancellation test. Migraineurs were randomized to three different preventive treatments: propranolol 40 mg tid, flunarizine 5 mg bid, or topiramate 50 mg bid. After 3 months of preventive treatment, migraineurs data were compared with their baseline values. The groups did not differ by sex and age. In electrophysiological studies, the habituation ability observed in the healthy group was not observed in migraineurs. However, it was restored 3 months after preventive treatment. In migraineurs, compared to their baseline values, the distorted visual attention parameters also improved after treatment. All drugs were effective. The loss of habituation ability and low visual attention performance in migraineurs can be restored by migraine preventive treatment. This electrophysiological study accompanied by neuropsychological test may aid an objective and quantitative assessment tool for understanding migraine pathophysiology.

Methylprednisolone blocks interleukin 1 beta induced calcitonin gene related peptide release in trigeminal ganglia cells

Background

Methylprednisolone (MPD) is a rapid acting highly effective cluster headache preventive and also suppresses the recurrence of migraine attacks. Previously, we could demonstrate that elevated CGRP plasma levels in a cluster headache bout are normalized after a course of high dose corticosteroids. Here we assess whether MPD suppresses interleukin-1β (IL-1β)- and prostaglandin E₂ (PGE₂)-induced CGRP release in a cell culture model of trigeminal ganglia cells, which could account for the preventive effect in migraine and cluster headache. Metoprolol(MTP), a migraine preventive with a slow onset of action, was used for comparison.

Methods

Primary cultures of rat trigeminal ganglia were stimulated for 24 h with 10 ng/ml IL-1β or for 4 h with 10 μM PGE₂ following the exposure to 10 or 100 μM MPD or 100 nM or 10 µM MTP for 45 min or 24 h. CGRP was determined by using a commercial enzyme immunoassay.

Results

MPD but not MTP blocked IL-1β-induced CGRP release from cultured trigeminal cells. PGE₂-stimulated CGRP release from trigeminal ganglia cell culture was not affected by pre-stimulation whether with MPD or MTP.

Conclusion

MPD but not MTP suppresses cytokine (IL-1β)-induced CGRP release from trigeminal ganglia cells. We propose that blockade of cytokine mediated trigeminal activation may represent a potential mechanism of action that mediates the preventive effect of MTP on cluster headache and recurrent migraine attacks.

Brain stimulation in migraine

Migraine is a very prevalent disease with great individual disability and socioeconomic burden. Despite intensive research effort in recent years, the etiopathogenesis of the disease remains to be elucidated. Recently, much importance has been given to mechanisms underlying the cortical excitability that has been suggested to be dysfunctional in migraine. In recent years, noninvasive brain stimulation techniques based on magnetic fields (transcranial magnetic stimulation, TMS) and on direct electrical currents (transcranial direct current stimulation, tDCS) have been shown to be safe and effective tools to explore the issue of cortical excitability, activation, and plasticity in migraine. Moreover, TMS, repetitive TMS (rTMS), and tDCS, thanks to their ability to interfere with and/or modulate cortical activity inducing plastic, persistent effects, have been also explored as potential therapeutic approaches, opening an interesting perspective for noninvasive neurostimulation for both symptomatic and preventive treatment of migraine and other types of headache. In this chapter we critically review evidence regarding the role of noninvasive brain stimulation in the pathophysiology and treatment of migraine, delineating the advantages and limits of these techniques together with potential development and future application.

Pearls and pitfalls: electrophysiology for primary headaches

BACKGROUND

Primary headaches are functional neurological diseases characterized by a dynamic cyclic pattern over time (ictal/pre-/interictal). Electrophysiological recordings can non-invasively assess the activity of an underlying nervous structure or measure its response to various stimuli, and are therefore particularly appropriate for the study of primary headaches. Their interest, however, is chiefly pathophysiological, as interindividual, and to some extent intraindividual, variations preclude their use as diagnostic tools.

AIM OF THE WORK

This article will review the most important findings of electrophysiological studies in primary headache pathophysiology, especially migraine on which numerous studies have been published.

RESULTS

In migraine, the most reproducible hallmark is the interictal lack of neuronal habituation to the repetition of various types of sensory stimulations. The mechanism subtending this phenomenon remains uncertain, but it could be the consequence of a thalamocortical dysrythmia that results in a reduced cortical preactivation level. In tension-type headache as well as in cluster headache, there seems to be an impairment of central pain-controlling mechanisms but the studies are scarce and their outcomes are contradictory. The discrepancies between studies might be as a result of methodological differences as well as patients' dissimilarities, which are also discussed.

CONCLUSIONS AND PERSPECTIVES

Electrophysiology is complementary to functional neuroimaging and will undoubtedly remain an important tool in headache research. One of its upcoming applications is to help select neurostimulation techniques and protocols that correct best the functional abnormalities detectable in certain headache disorders.