Cortical Excitability in Migraine and Epilepsy: A Common Feature?

Neurophysiological and Clinical Outcomes in Episodic Migraine Without Aura: A Cross-Sectional Study

PURPOSE

The aim of this study was to assess differences between people with episodic migraine and healthy controls in some neurophysiological and clinical outcomes, which, in turn, may highlight the differences in sensory processing, especially in cortical excitability, pain processing, and executive function.

METHODS

A cross-sectional study was performed, including the following outcomes: pressure pain thresholds with algometry; resting motor threshold, short-interval intracortical inhibition, and intracortical facilitation with transcranial magnetic stimulation; and executive functions with the trail making test and the frontal assessment battery.

RESULTS

Thirty adults with migraine (36 ± 10 years) and 30 healthy controls (29 ± 14 years) were included in this study. Compared with the healthy controls, participants with migraine presented lower pressure pain thresholds values in all the assessed muscles ( P < 0.001), lower resting motor threshold (-10.5% of the stimulator output, 95% CI: -16.8 to -4.2, P = 0.001, Cohen d = 0.869) and higher short-interval intracortical inhibition motor-evoked potential's amplitude at 3 ms (0.25, 95% CI: 0.05 to 0.46, P = 0.015, Cohen d = 0.662), and worse performances both in trail making test (7.1, 95% CI: 0.9 to 13.4, P = 0.027, Cohen d = 0.594) and frontal assessment battery (-1.1, 95% CI: -1.7 to -0.5, P = 0.001, Cohen d = 0.915).

CONCLUSIONS

Participants with migraine presented significant differences in cortical excitability, executive functions, and pressure pain thresholds, compared with healthy controls.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Inherited pain hypersensitivity and increased anxiety-like behaviors are associated with genetic epilepsy in Wistar Audiogenic Rats: Short- and long-term effects of acute and chronic seizures on nociception and anxiety

Anxiety and pain hypersensitivity are neurobehavioral comorbidities commonly reported by patients with epilepsies, and preclinical models are suitable to investigate the neurobiology of behavioral and neuropathological alterations associated with these epilepsy-related comorbidities. This work aimed to characterize endogenous alterations in nociceptive threshold and anxiety-like behaviors in the Wistar Audiogenic Rat (WAR) model of genetic epilepsy. We also assessed the effects of acute and chronic seizures on anxiety and nociception. WARs from acute and chronic seizure protocols were divided into two groups to assess short- and long-term changes in anxiety (1 day or 15 days after seizures, respectively). To assess anxiety-like behaviors, the laboratory animals were submitted to the open field, light-dark box, and elevated plus maze tests. The von Frey, acetone, and hot plate tests were used to measure the endogenous nociception in seizure-free WARs, and postictal antinociception was recorded at 10, 30, 60, 120, 180 min, and 24 h after seizures. Seizure-free WARs presented increased anxiety-like behaviors and pain hypersensitivity, displaying mechanical and thermal allodynia (to heat and cold stimuli) in comparison to nonepileptic Wistar rats. Potent postictal antinociception that persisted for 120 to 180 min was detected after acute and chronic seizures. Additionally, acute and chronic seizures have magnified the expression of anxiety-like behaviors when assessed at 1 day and 15 days after seizures. Behavioral analysis indicated more severe and persistent anxiogenic-like alterations in WARs submitted to acute seizures. Therefore, WARs presented pain hypersensitivity and increased anxiety-like behaviors endogenously associated with genetic epilepsy. Acute and chronic seizures induced postictal antinociception in response to mechanical and thermal stimuli and increased anxiety-like behaviors when assessed 1 day and 15 days later. These findings support the presence of neurobehavioral alterations in subjects with epilepsy and shed light on the use of genetic models to characterize neuropathological and behavioral alterations associated with epilepsy.

A Systematic Review of Long-Interval Intracortical Inhibition as a Biomarker in Neuropsychiatric Disorders

Long-interval intracortical inhibition (LICI) is a paired-pulse transcranial magnetic stimulation (TMS) paradigm mediated in part by gamma-aminobutyric acid receptor B (GABA_B) inhibition. Prior work has examined LICI as a putative biomarker in an array of neuropsychiatric disorders. This review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sought to examine existing literature focused on LICI as a biomarker in neuropsychiatric disorders. There were 113 articles that met the inclusion criteria. Existing literature suggests that LICI may have utility as a biomarker of GABA_B functioning but more research with increased methodologic rigor is needed. The extant LICI literature has heterogenous methodology and inconsistencies in findings. Existing findings to date are also non-specific to disease. Future research should carefully consider existing methodological weaknesses and implement high-quality test-retest reliability studies.

Headache in epilepsy: A prospective observational study

OBJECTIVE

To assess the frequency and characteristics of interictal and postictal headaches (using International Classification of Headache Disorders, 3rd edition criteria) in a population of patients with epilepsy admitted to the Mayo Clinic Rochester epilepsy monitoring unit and assess their localizing value.

METHODS

This was a cross-sectional study. Participants were voluntarily recruited upon admission to the epilepsy monitoring unit. Two separate questionnaires were then administered. The first was to assess the presence and character of headaches experienced in the past 12 months. The second was to assess characteristics of postictal headaches experienced during their admission including localization.

RESULTS

One-hundred and twenty subjects (77%) met inclusion criteria and completed the initial questionnaire. Mean age was 38.1 years (range 18-82), and 67 (55.8%) were female. Interictal headaches were reported in 97 of 120 (81%) subjects, and these met ICHD3 criteria for migraine in 48 (50%). Postictal headaches were reported by 75 of 120 (63%) subjects on the initial admission questionnaire, representing migraine in 38 (51%). Thirty-nine (32%) subjects completed the secondary questionnaire related to postictal headaches experienced during admission, of which nine (23%) met criteria for migraine. There was no seizure lateralizing or localizing value noted based on postictal headache localization.

SIGNIFICANCE

Migraine was frequent in this cohort and appears to be the dominant interictal and postictal headache type in patients with epilepsy. In this study, the first to assess incident postictal headache in the setting of an ictal EEG, headache localization was of no seizure localizing value. Few patients were being actively treated; suggesting headache management is often overlooked in the epilepsy population.

Does pain sensitivity increase during ictal period? Evidence from absence epileptic WAG/Rij rats

OBJECTIVE

The hyperexcitable brain provides a common ground for comorbidity of pain syndromes and epilepsy. There are controversial reports about pain sensitivity during the ictal period. We analyzed the pain sensitivity during the ictal period in the genetic absence epilepsy animal model, Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats.

METHODS

The ictal and interictal pain sensitivities of symptomatic WAG/Rij rats (8 months old, n = 19) were determined and compared with those of age-matched control Wistar rats (n = 19). Pain sensitivity was assessed by applying heat stimulation to hind paws and measuring the paw-withdrawal latency using a thermal plantar analgesia meter in awake and freely moving animals. All measurements were made during the interictal and ictal periods and confirmed by simultaneous electroencephalography (EEG) through intracranially implanted electrodes.

RESULTS

The nociceptive stimulus-induced withdrawal latency during the ictal period in absence epilepsy WAG/Rij rats was significantly shorter when compared with that during the interictal period (p = 0.007) and when compared with that in the control Wistar rats (p = 0.001).

CONCLUSION

Our data indicate higher pain sensitivity during the ictal period in absence epilepsy rats. Considering the fact that subjects are less responsive during spike-wave discharges, there is a decrease in the level of consciousness and/or responsiveness ictally during all generalized genetic seizures, this increased pain sensitivity is rather surprising during the ictal period. Although the mechanism remains unknown, this novel finding deserves further investigation.

Long-interval intracortical inhibition as biomarker for epilepsy: a transcranial magnetic stimulation study

Cortical excitability, as measured by transcranial magnetic stimulation combined with electromyography, is a potential biomarker for the diagnosis and follow-up of epilepsy. We report on long-interval intracortical inhibition data measured in four different centres in healthy controls (n = 95), subjects with refractory genetic generalized epilepsy (n = 40) and with refractory focal epilepsy (n = 69). Long-interval intracortical inhibition was measured by applying two supra-threshold stimuli with an interstimulus interval of 50, 100, 150, 200 and 250 ms and calculating the ratio between the response to the second (test stimulus) and to the first (conditioning stimulus). In all subjects, the median response ratio showed inhibition at all interstimulus intervals. Using a mixed linear-effects model, we compared the long-interval intracortical inhibition response ratios between the different subject types. We conducted two analyses; one including data from the four centres and one excluding data from Centre 2, as the methods in this centre differed from the others. In the first analysis, we found no differences in long-interval intracortical inhibition between the different subject types. In all subjects, the response ratios at interstimulus intervals 100 and 150 ms showed significantly more inhibition than the response ratios at 50, 200 and 250 ms. Our second analysis showed a significant interaction between interstimulus interval and subject type (P = 0.0003). Post hoc testing showed significant differences between controls and refractory focal epilepsy at interstimulus intervals of 100 ms (P = 0.02) and 200 ms (P = 0.04). There were no significant differences between controls and refractory generalized epilepsy groups or between the refractory generalized and focal epilepsy groups. Our results do not support the body of previous work that suggests that long-interval intracortical inhibition is significantly reduced in refractory focal and genetic generalized epilepsy. Results from the second analysis are even in sharper contrast with previous work, showing inhibition in refractory focal epilepsy at 200 ms instead of facilitation previously reported. Methodological differences, especially shorter intervals between the pulse pairs, may have contributed to our inability to reproduce previous findings. Based on our results, we suggest that long-interval intracortical inhibition as measured by transcranial magnetic stimulation and electromyography is unlikely to have clinical use as a biomarker of epilepsy.

Epilepsy may cause increased pain sensitivity: Evidence from absence epileptic WAG/Rij rats

OBJECTIVE

The comorbidity of epilepsy and pain disorders as well as effectiveness of certain therapeutic approaches in both conditions attracted attention to epilepsy-pain interactions. This lead to the discovery of significantly shared pathophysiological mechanisms although many aspects remain largely unknown. To test the hypothesis that epilepsy may be associated with altered pain sensitivity, we analyzed interictal pain sensitivity using epilepsy prone WAG/Rij rats, a genetic model exhibiting age-related-onset absence epilepsy.

METHODS

Two series of experiments were conducted. In experiment I, pain sensitivity of symptomatic WAG/Rij rats were compared with age-matched control Wistar rats. In experiment II, pain sensitivity of WAG/Rij rats were monitored longitudinally when they were presymptomatic (at 2months) and symptomatic (after maturation, at 8months), and compared with age-matched control Wistar rats. Pain sensitivity was assessed by applying heat stimuli to hind paws and measuring the paw-withdrawal latency using thermal plantar analgesia meter in awake and freely moving animals. All pain measurements were made during the interictal period, confirmed by simultaneous electroencephalography through intracranially implanted electrodes.

RESULTS

In experiment I, the interictal pain withdrawal latency of symptomatic WAG/Rij rats was significantly shorter than control Wistar rats (P<0.01). In experiment II, WAG/Rij rats had significantly shorter latency of withdrawal response than control Wistar rats, both at presymptomatic (P<0.05) and symptomatic stage (P<0.0001). Matured (8months old) control Wistar rats demonstrated significantly increased withdrawal latency compared to the 2months animals (P<0.01), but the WAG/Rij rats did not (P>0.5).

CONCLUSION

Epileptic WAG/Rij rats present significantly increased pain sensitivity when compared to control Wistar rats, suggesting comorbidity of epilepsy and pain.

Cathodal transcranial direct-current stimulation for treatment of drug-resistant temporal lobe epilepsy: A pilot randomized controlled trial

Objective

To investigate the effect of cathodal transcranial direct‐current stimulation (c‐tDCS) on seizure frequency in patients with drug‐resistant temporal lobe epilepsy (TLE).

Method

Twenty‐nine patients with drug‐resistant TLE participated in this study. They were randomized to experimental or sham group. Twenty participants (experimental group) received within‐session repeated c‐tDCS intervention over the affected temporal lobe, and nine (sham group) received sham tDCS. Paired‐pulse transcranial magnetic stimulation was used to assess short interval intracortical inhibition (SICI) in primary motor cortex ipsilateral to the affected temporal lobe. SICI was measured from motor evoked potentials recorded from the contralateral first dorsal interosseous muscle. Adverse effects were monitored during and after each intervention in both groups. A seizure diary was given to each participant to complete for 4 weeks following the tDCS intervention. The mean response ratio was calculated from their seizure rates before and after the tDCS intervention.

Results

The experimental group showed a significant increase in SICI compared to the sham group (F = 10.3, p = 0.005). None of the participants reported side effects of moderate or severe degree. The mean response ratio in seizure frequency was −42.14% (standard deviation [SD] 35.93) for the experimental group and −16.98% (SD 52.41) for the sham group.

Significance

Results from this pilot study suggest that tDCS may be a safe and efficacious nonpharmacologic intervention for patients with drug‐resistant TLE. Further evaluation in larger double‐blind randomized controlled trials is warranted.

Computational modeling of neurostimulation in brain diseases

Neurostimulation as a therapeutic tool has been developed and used for a range of different diseases such as Parkinson's disease, epilepsy, and migraine. However, it is not known why the efficacy of the stimulation varies dramatically across patients or why some patients suffer from severe side effects. This is largely due to the lack of mechanistic understanding of neurostimulation. Hence, theoretical computational approaches to address this issue are in demand. This chapter provides a review of mechanistic computational modeling of brain stimulation. In particular, we will focus on brain diseases, where mechanistic models (e.g., neural population models or detailed neuronal models) have been used to bridge the gap between cellular-level processes of affected neural circuits and the symptomatic expression of disease dynamics. We show how such models have been, and can be, used to investigate the effects of neurostimulation in the diseased brain. We argue that these models are crucial for the mechanistic understanding of the effect of stimulation, allowing for a rational design of stimulation protocols. Based on mechanistic models, we argue that the development of closed-loop stimulation is essential in order to avoid inference with healthy ongoing brain activity. Furthermore, patient-specific data, such as neuroanatomic information and connectivity profiles obtainable from neuroimaging, can be readily incorporated to address the clinical issue of variability in efficacy between subjects. We conclude that mechanistic computational models can and should play a key role in the rational design of effective, fully integrated, patient-specific therapeutic brain stimulation.

High prevalence of headaches in patients with epilepsy

Background

To examine the association between headaches and epilepsy.

Methods

Consecutive adult epileptic patients who went to the outpatient clinic of the Epilepsy Center of PLA General Hospital between February 01, 2012, and May 10, 2013, were recruited into this study. A total of 1109 patients with epilepsy completed a questionnaire regarding headaches.

Results

Overall, 60.1% of the patients (male: 57.2%; female: 63.8%) reported headaches within the last year. The age-weighted prevalence of interictal migraine was 11.7% (male 8.9%, female 15.3%), which is higher than that reported in a large population-based study (8.5%, male 5.4%, female 11.6%) using the same screening questions. The prevalence of postictal headaches was 34.1% (males 32.7%, females 35.2%), and the presence of preictal headaches was 4.5% (males 4.3%, females 5.2%). The prevalence of headache yesterday in the general population was 4.8% (male 3.0%, female 6.6%). Thus, the prevalence of headaches, including migraine, is higher in epileptic patients in China.

Conclusions

The high prevalence of postictal headaches confirms the frequent triggering of a headache by a seizure. A much lower frequency of preictal headaches, a condition in which the real triggering effect of the headache on the seizure might be difficult to prove.

CORTICAL EXCITABILITY AS A POTENTIAL CLINICAL MARKER OF EPILEPSY: A REVIEW OF THE CLINICAL APPLICATION OF TRANSCRANIAL MAGNETIC STIMULATION

Transcranial magnetic stimulation (TMS) can be used for safe, noninvasive probing of cortical excitability (CE). We review 50 studies that measured CE in people with epilepsy. Most showed cortical hyperexcitability, which can be corrected with anti-epileptic drug treatment. Several studies showed that decrease of CE after epilepsy surgery is predictive of good seizure outcome. CE is a potential biomarker for epilepsy. Clinical application may include outcome prediction of drug treatment and epilepsy surgery.

On the midway to epilepsy: is cortical excitability normal in patients with isolated seizures?

Paired pulse transcranial magnetic stimulation was used to investigate differences in cortical excitability between patients with isolated (unrecurrent, unprovoked) seizures and those with epilepsy. Compared to controls, cortical excitability was higher in the isolated seizure group at 250-300 ms. Compared to epilepsy, cortical excitability was lower in patients with isolated seizures also at 250 and 300 ms. Lowered seizure threshold caused by disturbances within inhibitory circuits is present in patients who experience a seizure even if no further seizures occur.

Altered cortical GABAA receptor composition, physiology, and endocytosis in a mouse model of a human genetic absence epilepsy syndrome

Patients with generalized epilepsy exhibit cerebral cortical disinhibition. Likewise, mutations in the inhibitory ligand-gated ion channels, GABAA receptors (GABAARs), cause generalized epilepsy syndromes in humans. Recently, we demonstrated that heterozygous knock-out (Hetα1KO) of the human epilepsy gene, the GABAAR α1 subunit, produced absence epilepsy in mice. Here, we determined the effects of Hetα1KO on the expression and physiology of GABAARs in the mouse cortex. We found that Hetα1KO caused modest reductions in the total and surface expression of the β2 subunit but did not alter β1 or β3 subunit expression, results consistent with a small reduction of GABAARs. Cortices partially compensated for Hetα1KO by increasing the fraction of residual α1 subunit on the cell surface and by increasing total and surface expression of α3, but not α2, subunits. Co-immunoprecipitation experiments revealed that Hetα1KO increased the fraction of α1 subunits, and decreased the fraction of α3 subunits, that associated in hybrid α1α3βγ receptors. Patch clamp electrophysiology studies showed that Hetα1KO layer VI cortical neurons exhibited reduced inhibitory postsynaptic current peak amplitudes, prolonged current rise and decay times, and altered responses to benzodiazepine agonists. Finally, application of inhibitors of dynamin-mediated endocytosis revealed that Hetα1KO reduced base-line GABAAR endocytosis, an effect that probably contributes to the observed changes in GABAAR expression. These findings demonstrate that Hetα1KO exerts two principle disinhibitory effects on cortical GABAAR-mediated inhibitory neurotransmission: 1) a modest reduction of GABAAR number and 2) a partial compensation with GABAAR isoforms that possess physiological properties different from those of the otherwise predominant α1βγ GABAARs.