Functional neuroimaging of headaches

A new trigemino-nociceptive stimulation model for event-related fMRI

Functional imaging of human trigemino-nociceptive processing provides meaningful insights into altered pain processing in head and face pain diseases. Although functional magnetic resonance imaging (fMRI) offers high temporal and spatial resolution, most studies available were done with radioligand-positron emission tomography, as fMRI requires non-magnetic stimulus equipment and fast on–off conditions. We developed a new approach for painful stimulation of the trigeminal nerve that can be implemented within an event-related design using fMRI and aimed to detect increased blood-oxygen-level-dependent (BOLD) signals as surrogate markers of trigeminal pain processing. Using an olfactometer, 20 healthy volunteers received intranasally standardized trigeminal nociceptive stimuli (ammonia gas) as well as olfactory (rose odour) and odourless control stimuli (air puffs). Imaging revealed robust BOLD responses to the trigeminal nociceptive stimulation in cortical and subcortical brain areas known to be involved in pain processing. Focusing on the trigeminal pain pathway, significant activations were observed bilaterally in brainstem areas at the trigeminal nerve entry zone, which are agreeable with the principal trigeminal nuclei. Furthermore, increased signal changes could be detected ipsilaterally at anatomical localization of the trigeminal ganglion and bilaterally in the rostral medulla, which probably represents the spinal trigeminal nuclei. However, brainstem areas involved in the endogenous pain control system that are close to this anatomical localization, such as raphe nuclei, have to be discussed. Our findings suggest that mapping trigeminal pain processing using fMRI with this non-invasive experimental design is feasible and capable of evoking specific activations in the trigeminal nociceptive system. This method will provide an ideal opportunity to study the trigeminal pain system in both health and pathological conditions such as idiopathic headache disorders.

Verapamil for cluster headache. Clinical pharmacology and possible mode of action

Verapamil is used mainly in cardiovascular diseases. High-dose verapamil (360-720 mg) is, however, currently the mainstay in the prophylactic treatment of cluster headache. The oral pharmacokinetics are variable. The pharmacodynamic effect of verapamil, the effect on blood pressure, also varies considerably among subjects. The dose of verapamil used for cluster headache is approximately double the dose used in cardiovascular disease, most likely because verapamil is a substrate for the efflux transporter P-glycoprotein in the blood-brain barrier. The access of verapamil to the central nervous system is therefore limited. The clinical use of verapamil in cluster headache is reviewed and several relevant drug interactions are mentioned. Finally, its possible mode of action in cluster headache is discussed. The effect of verapamil in cluster headache most likely takes place in the hypothalamus.Verapamil is an L-type calcium channel blocker but it is also a blocker of other calcium channels (T-, P-, and possibly N- and Q-type Ca(2+) channels) and the human ether-a-go-go-related gene potassium channel. With so many different actions of verapamil, it is impossible at the present time to single out a certain mode of action of the drug in cluster headache.

The headache of a hyperactive calcium channel

Migraine is thought to be triggered by excessive neocortical neuronal excitability that leads to cortical spreading depression. In this issue of Neuron, Tottene et al. study a mouse model of familial hemiplegic migraine type 1, and provide evidence for the hyperactivity of P/Q-type calcium channel-mediated cortical glutamatergic synaptic transmission as an underlying mechanism for the susceptibility of cortical spreading depression initiation in migraine disorders.

Headache and migraine

The application of modern imaging techniques to the study of patients with headache/migraine has dramatically changed our understanding of these conditions. Several studies of these patients have demonstrated not only the occurrence of abnormalities of function, but also relevant and diffuse structural changes of the brain white and grey matter. More recently, it has been suggested that the different forms of headache/migraine might have specific functional and structural MRI correlates, which, in the future, is likely to result in new therapeutic scenarios.

Functional magnetic resonance imaging in episodic cluster headache

We have investigated the cerebral activation centre in four patients with episodic cluster headache (CH) with functional magnetic resonance imaging (f-MRI). The patients underwent MRI scans for anatomical and functional data acquisition in the asymptomatic state, during a headache attack and after subcutaneous administration of sumatriptan. Anatomical images were acquired by means of 3D-MPRAGE sequences and f-MRI images were obtained by means of echo-planar imaging. Data was analysed using the BrainVoyager QX version 1.7.81 software package. In all patients, the data showed significant hypothalamic activation of the hypothalamus ipsilateral to the pain side, attributable to a headache attack. Overall, we have demonstrated the anatomical location of central nervous system activation by means the first f-MRI study in CH patients. f-MRI offers a good balance of spatial and temporal resolution, and this method of study appears appropriate for investigating the pathogenetic aspects of primary headaches. Positron emission tomography and f-MRI may be regarded as little or no importance in a clinical context, they do, however, offer great potential for the exploration of headache physiopathology and the effects of pharmacological treatment.

Possible pathogenic link between migraine and urotensin-II

Our aim was to determine the levels of human urotensin-II (hU-II) in the plasma of migraine patients and controls, to ascertain if there were a difference in the pathogenesis of migraine. A total of 27 patients who suffer from migraines and 27 controls were included in the study. Venous blood samples were drawn twice both from migraine patients and controls to measure hU-II plasma levels. The average levels of hU-II during migraine episode, between episodes, and controls were found to be 0.483, 0.493, and 0.737 pg/mL, respectively. The levels of hU-II in the controls were higher significantly. When comparisons were made according to sex, age groups, and types and durations of migraine, there was no significant difference in the levels of hU-II in the patients. The low levels of hU-II in the plasma of migraine patients compared with controls may be an indicator of its role in the pathogenesis.

Binocular rivalry in migraine

Cortical hyperexcitability in migraine could arise from abnormally weak inhibition or from strengthened intracortical excitatory mechanisms. The present study employed binocular rivalry to differentiate between these possibilities. Rivalry between static oriented grating patterns was examined in migraine with aura (MA), migraine without aura (MoA) and headache-free control participants. A non-significant trend toward elevated mean dominance intervals (monocular percepts, in seconds) was seen in both migraine groups at all contrasts. Second, significant interocular differences in rivalry dominance durations were seen in the MoA group compared with controls; this difference also approached significance in the MA group. Finally, both MA and MoA exhibited significantly greater visual discomfort than the control group in the presence of both static stripes and flickering visual stimuli. The rivalry results provide no support for weakened intracortical inhibition in migraine. Optical or neural precortical differences in the eyes' input strengths paired with enhanced recurrent cortical excitation can explain these findings.

[Cortical dysbalance in the brain in migraineurs--hyperexcitability as the result of sensitisation?]

A cortical dysbalance has a pivotal role in the pathophysiology of migraine. Numerous electrophysiological and transcranial magnetic stimulation (TMS) studies have investigated the interictal excitability level in migraineurs and have shown a consistent lack of habituation during repetitive stimulation. There is some controversy in the current literature over whether this deficit is based on a lowered or an elevated preactivation level. However, the current discussion may be misguided. It seems that multiple external and intrinsic factors influence the level of cortical excitability and the frequency and intensity of attacks: Habituation is specific neither to migraine nor even to pain; the same phenomenon is found in tinnitus patients, for example. Cortical hyperexcitability is presumably the result of chronicity and the concomitant central sensitisation process.

Hypothalamic activation in spontaneous migraine attacks

BACKGROUND

Migraine sufferers experience premonitory symptoms which suggest that primary hypothalamic dysfunction is a likely trigger of the attacks. Neuroendocrine and laboratory data also support this hypothesis. To date, positron emission tomography (PET) scans of migraine sufferers have demonstrated activation of brainstem nuclei, but not of the hypothalamus.

OBJECTIVE

To record cerebral activations withH2 15OPET during spontaneous migraine without aura attacks.

METHODS

We scanned 7 patients with migraine without aura (6 females and 1 male) in each of 3 situations: within 4 hours of headache onset, after headache relief by sumatriptan injection (between the fourth and the sixth hour after headache onset), and during an attack-free period.

RESULTS

During the headache we found not only significant activations in the midbrain and pons, but also in the hypothalamus, all persisting after headache relief by sumatriptan.

CONCLUSION

Hypothalamic activity, long suspected by clinical and experimental arguments as a possible trigger for migraine, is demonstrated for the first time during spontaneous attacks.

Clinical correlates of phosphene perception in migraine without aura: An Asian study

INTRODUCTION

Although controversy exists with regard to the presence of hypoexcitability versus hyperexcitability of the visual cortex in migraine patients, there remain a group who do not perceive phosphenes (P-). However, its clinical implications have not been systematically addressed. In this study, we hypothesize that P- patients classified as migraine without aura (MO) have distinct clinical features.

METHODS

Twenty-nine Asian MO patients (7 men; mean age: 44; median: 45; range: 25 to 65) were consecutively entered into the study. Visual cortex transcranial magnetic stimulation (TMS) was performed in the migraine interictum.

RESULTS

Of the 19 patients, 19 (66%) were able to perceive phosphenes (P+), while 10 (34%) were not able to after repeated TMS (P-). P- patients had significantly higher headache frequency (p=0.008) and pain score (p=0.002) compared with P+ patients. In addition, there was significant positive correlation of phosphene threshold with pain score (r=0.52, p=0.02) in P+ patients. There was no significant difference between P+ and P- patients in terms of age (t-test, p=0.6).

CONCLUSIONS

Our study is inkeeping with the hypothesis that interictal visual cortex excitability is reduced in relation to the severity of migraine in Asian MO patients, and lack of phosphene perception may be related to significantly elevated thresholds beyond the output of TMS stimulators.

Connectivity of an effective hypothalamic surgical target for cluster headache

The purpose of this study was to look at the connectivity of the posterior inferior hypothalamus in a patient implanted with a deep brain stimulating electrode using probabilistic tractography in conjunction with postoperative MRI scans. In a patient with chronic cluster headache we implanted a deep brain stimulating electrode into the ipsilateral postero-medial hypothalamus to successfully control his pain. To explore the connectivity, we used the surgical target from the postoperative MRI scan as a seed for probabilistic tractography, which was then linked to diffusion weighted imaging data acquired in a group of healthy control subjects. We found highly consistent connections with the reticular nucleus and cerebellum. In some subjects, connections were also seen with the parietal cortices, and the inferior medial frontal gyrus. Our results illustrate important anatomical connections that may explain the functional changes associated with cluster headaches and elucidate possible mechanisms responsible for triggering attacks.

New insights into migraine: application of functional and structural imaging

PURPOSE OF REVIEW

Functional neuroimaging in headache patients has revolutionized our understanding of these syndromes. Further insights into the pathophysiology of headache syndromes have been provided by innovative neuroimaging analysis using structural data. This review highlights the recent advances made in studying migraine using neuroimaging techniques.

RECENT FINDINGS

Several independent studies have reinforced the crucial role for the brainstem in acute and probably also chronic migraine. Recently described structural abnormalities in the visual network of motion-processing areas could account for, or be caused by, the cortical hyperexcitability observed in migraineurs. Although data from morphometric studies are heterogeneous, a recent study suggests an increased density of brainstem structures and decreased grey matter in pain-transmitting areas in migraine patients.

SUMMARY

Given the rapid advances in functional neuroimaging, in particular newer techniques such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a significant role and opens new avenues in targeting the neural substrates in individual primary headache syndromes.

New Migraine and Pain Research

An understanding of the pathophysiology and pharmacology of migraine has been driven by astute clinical observations, elegant experimental medicine studies and importantly by the introduction of highly effective selective anti-migraine agents such as the Triptan 5-HT(1B/1D) agonists. New investigational migraine therapies such CGRP antagonists target key components of the trigeminal sensory neuroinflammatory response and show promise for the future. Cutting edge molecular profiling studies looking at gene expression during chronic pain are now being used to reveal the cell biology of pain and new potential therapeutic targets. Translational neuroimaging research can link the laboratory and the clinic and is now being used to help understand the neural systems biology of migraine. Research into migraine has generated sophisticated hypotheses that encompass primary CNS dysfunction, trigeminovascular activation, pain perception and activation of associated neural circuits involved in affective functions providing a rich framework within which to design and test future migraine treatment strategies.

The physical examination of migraine

Patients and physicians are frequently unaware that pain coming from the muscles of the head and neck is probably the cause of the most frequent forms of migraine. Identifying the extracranial origins of the patient's headache by physical examination should reassure patient and examiner that the headache is benign and treatable. The results of the examination should lead to physical treatment, reducing headache frequency and severity. This paper describes techniques of the physical examination to identify the extracranial causes of migraine headache.

Case Series of Four Different Headache Types Presenting as Tooth Pain

Case reports in the literature discuss various headache disorders that present as pain in the face. The current understanding of neuroanatomy and headache mechanisms suggests that headache pain originates within intracranial structures and is then referred to the face, jaws, and teeth. This case series describes four patients, one each with migraine headache, cluster headache, paroxysmal hemicrania, and hemicrania continua, all of which who presented to dentists with the chief complaint of tooth pain. This is the first report of hemicrania continua presenting as tooth pain. It is important that dentists be cognizant of headache disorders so that they may be able to identify headache pains masquerading as toothache.

Deep brain stimulation in headache

BACKGROUND

The therapeutic use of deep brain stimulation to relieve intractable pain began in the 1950s. In some patients, stimulation of the periaqueductal grey matter induced headache with migrainous features, indicating a pathophysiological link between neuromodulation of certain brain structures and headache.

RECENT DEVELOPMENTS

Neuroimaging studies have revealed specific activation patterns in various primary headaches. In the trigeminal autonomic cephalgias, neuroimaging findings support the hypothesis that activation of posterior hypothalamic neurons have a pivotal role in the pathophysiology and prompted the idea that hypothalamic stimulation might inhibit this activation to improve or eliminate the pain in intractable chronic cluster headache and other trigeminal autonomic cephalgias. Over the past 6 years, hypothalamic implants have been used in various centres in patients with intractable chronic cluster headache. The results are encouraging: most patients achieved stable and notable pain reduction and many became pain free. All deep-brain-electrode implantation procedures carry a small risk of mortality due to intracerebral haemorrhage. Before implantation, all patients must undergo complete preoperative neuroimaging to exclude disorders associated with increased haemorrhagic risk. No substantial changes in hypothalamus-controlled functions have been reported during hypothalamic stimulation. Hypothalamic stimulation may also be beneficial in patients with SUNCT (short-lasting, unilateral, neuralgiform headache attacks with conjunctival injection and tearing)--a disorder with close clinical and neuroimaging similarities to the cluster headache. WHERE NEXT?: Neuroimaging findings in patients undergoing posterior hypothalamic stimulation have shown activation of the trigeminal nucleus and ganglion. This evidence supports the hypothesis that hypothalamic stimulation exerts its effect by modulating the activity of the trigeminal nucleus caudalis, which in turn might control the brainstem trigeminofacial reflex--thought to cause cluster headache pain. Future studies might determine whether other areas of the pain matrix are suitable targets for neuromodulation in patients with cluster headache who do not respond to hypothalamic modulation.

Cluster headache: orbital hemodynamic changes during Valsalva maneuver

BACKGROUND

The clinical features of cluster headache (CH) disclose some vascular changes in the symptomatic region, but few instrumental studies have assessed orbital hemodynamics in patients with this disorder.

METHODS

Orbital blood flow reactivity elicited by Valsalva maneuver (VM) was studied with ophthalmic artery eco-Doppler in 16 patients (14 men and 2 women; mean age: 41.2) suffering from episodic CH and in 18 healthy controls. Patients were examined twice: first, in a cluster period (between pain attacks), and second, in a remission period. Each time peak-systolic and end-diastolic flow velocities were recorded in both ophthalmic arteries at rest and during all phases of VM.

RESULTS

Valsalva phase IV was consistently associated with an increment of blood flow velocities through the ophthalmic arteries. Unlike controls, patients showed an asymmetric vascular reactivity. In the cluster period peak-systolic flow velocity increments were lower on the symptomatic side than on the asymptomatic side (14.1% vs. 34.4%; P < .001), while in remission end-diastolic flow velocity increments were higher in the previously symptomatic orbit (129% vs. 72.9%; P < .05). Vascular reactivity on the asymptomatic side was always similar to that of healthy controls.

CONCLUSIONS

In episodic CH, the symptomatic orbit shows an abnormal vascular reactivity. During the cluster period, basal vasodilation and hyperemia could preclude it from admitting a much greater amount of blood at the end of Valsalva. During remission, there might be some latent vascular changes that lead to supersensitive vasodilator responses and/or opening of arteriovenous shunts under certain circumstances such as Valsalva. These phenomena could be relevant in the pathophysiology of CH.

A sleep study in cluster headache

Cluster headache (CH) is a primary headache with a close relation to sleep. CH presents a circa-annual rhythmicity; attacks occur preferably during the night, in rapid eye movement (REM) sleep, and they are associated with autonomic and neuroendocrine modifications. The posterior hypothalamus is the key structure for the biological phenomenon of CH. Our aim is to describe a 55-year-old man presenting a typical episodic CH, in whom we performed a prolonged sleep study, consisting of a 9-week actigraphic recording and repeated polysomnography, with evaluation of both sleep macrostructure and microstructure. During the acute bout of the cluster we observed an irregular sleep-wake pattern and abnormalities of REM sleep. After the cluster phase these alterations remitted. We conclude that CH was associated, in this patient, with sleep dysregulation involving the biological clock and the arousal mechanisms, particularly in REM. All these abnormalities are consistent with posterior hypothalamic dysfunction.

Cluster headache pharmacotherapy

Cluster headache is a well-known primary headache syndrome with a prevalence of about 5/10,000 of the adult population, making it much less common than migraine. Diagnostic terms such as histaminic cephalalgia, Horton's headache and ciliary neuralgia have been used for what is now known as cluster headache. This disorder can be differentiated from migraine by clinical and pathophysiologic features. Cluster headache also exhibits a differing therapeutic response to medications when compared with migraine. The pharmacologic treatment of cluster is reviewed in this article. In contrast to migraine, men are 3-4 times more likely to be diagnosed with cluster headache than women, and the cluster headache population is older. Cluster attacks are known for their brief intense unilateral excruciating pain during susceptible periods known as cluster periods, which typically last weeks. Attack-free months generally follow. Pain is experienced in the distribution of the trigeminal nerve, with unilateral autonomic features. Most patients are successfully managed with medical therapy. Medication management can be divided into abortive treatments for an ongoing attack and prophylactic treatment. Prophylaxis aims to induce and maintain a remission. There are a variety of different medications for abortive and prophylactic therapy, accompanied by a variable amount of evidence-based medicine. For patients refractory to medical management, interventional procedures are available as a last resort. Most procedures are directed against the sensory trigeminal nerve and associated ganglia, eg, anesthetizing the sphenopalatine ganglion.

Role of functional imaging in neurological disorders

Neuroimaging in recent years has greatly contributed to our understanding of a wide range of aspects related to central neurological diseases. These include the classification and localization of disease, such as in headache; the understanding of pathology, such as in Parkinson's disease (PD); the mechanisms of reorganization, such as in stroke and multiple sclerosis (MS); and the subclinical progress of disease, such as in amyotrophic lateral sclerosis (ALS). Apart from presurgical mapping, however, the clinical applications so far are limited. Nevertheless, functional imaging does enable the formulation of neurobiological hypotheses that can be tested clinically, and thus is well suited for testing classic clinical hypotheses about how the brain works. Understanding the mechanisms and sites of pathology, such as has been achieved in cluster headaches, facilitates the development of new therapeutic strategies.

The role of imaging in the pathophysiology and diagnosis of headache

PURPOSE OF REVIEW

Functional neuroimaging in headache patients has revolutionized our understanding of these syndromes and provided unique insights into some of the most common maladies in humans, suggesting that at least migraine and cluster headache are driven primarily from the brain. This review highlights new studies and recent advances in studying headache using neuroimaging.

RECENT FINDINGS

Concerning the diagnostics of headache, an EFNS Task Force evaluated recently the usefulness of imaging procedures in non-acute headache patients on the basis of evidence from the literature and defined guidelines on when to use magnetic resonance imaging or computed tomography. Regarding the pathophysiology of primary headache syndromes, repeated and independent findings reinforce the crucial role for the brainstem in acute and probably also in chronic migraine, and the hypothalamic grey in several trigemino-autonomic headaches. If further studies confirm these findings, a better understanding will be gained of where and how acute and preventive therapy can be targeted.

SUMMARY

Given the rapid advances in functional neuroimaging, in particular newer techniques such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a significant role and opens new avenues in targeting the neural substrates in individual primary headache syndromes.