Brainstem activation specific to migraine headache

Imaging Findings of Migraine

Increasingly sophisticated neuroimaging techniques have allowed researchers to begin to define functional and anatomical characteristics of migraine. This paper reviews current knowledge and techniques employed. Assessing present-day knowledge limitations it concludes that with parallel advances in the technology of imaging and the pathophysiologic understanding of migraine, a reliable biomarker may be discovered in the future.

Brain gray matter changes in migraine patients with T2-visible lesions: a 3-T MRI study

BACKGROUND AND PURPOSE

In migraine patients, functional imaging studies have shown changes in several brain gray matter (GM) regions. However, 1.5-T MRI has failed to detect any structural abnormality of these regions. We used a 3-T MRI scanner and voxel-based morphometry (VBM) to assess whether GM density abnormalities can be seen in patients with migraine with T2-visible abnormalities and to grade their extent.

METHODS

In 16 migraine patients with T2-visible abnormalities and 15 matched controls, we acquired a T2-weighted and a high-resolution T1-weighted sequence. Lesion loads were measured on T2-weighted images. An optimized version of VBM analysis was used to assess regional differences in GM densities on T1-weighted scans of patients versus controls. Statistical parametric maps were thresholded at P<0.001, uncorrected for multiple comparisons.

RESULTS

Compared with controls, migraine patients had areas of reduced GM density, mainly located in the frontal and temporal lobes. Conversely, patients showed increased periacqueductal GM (PAG) density. Compared with patients without aura, migraine patients with aura had increased density of the PAG and of the dorsolateral pons. In migraine patients, reduced GM density was strongly related to age, disease duration, and T2-visible lesion load (r ranging from -0.84 to -0.73).

CONCLUSIONS

Structural GM abnormalities can be detected in migraine patients with brain T2-visible lesions using VBM and a high-field MRI scanner. Such GM changes comprise areas with reduced and increased density and are likely related to the pathological substrates associated with this disease.

New insights into brain dysfunction in migraine

Headache is one of the most common presenting symptoms to a physician's office. The majority of headaches are in the category known as primary headaches, where there are no structural disturbances. Secondary headaches are uncommon and usually occur in less than 10% of patients. The mechanisms of secondary headaches are usually due to the underlying pathology. These are usually evident on neuroimaging or laboratory testing. This review will focus mainly on mechanisms of primary headache (i.e., migraine and cluster).

Posterior hypothalamic activation in paroxysmal hemicrania

OBJECTIVE

Paroxysmal hemicrania (PH) is a severe, strictly unilateral headache that lasts 2 to 30 minutes, occurs more than five times daily, is associated with trigeminal autonomic symptoms, and is exquisitely responsive to indomethacin. The purpose of the study was to determine the brain structures active in PH.

METHODS

Seven PH patients were studied using positron emission tomography (PET). Each patient was scanned in three states: (1) acute PH attack-off indomethacin; (2) pain-free-off indomethacin; and (3) pain-free after administration of intramuscular indomethacin 100 mg. The scan images were processed and analyzed using SPM99.

RESULTS

The study showed no significant activations during state 1 compared with state 2, but there was relative activation of the pain neuromatrix in both states 1 and 2 compared with state 3. This suggests that there is persistent activation of the pain neuromatrix during acute PH attacks and during interictal pain-free states off indomethacin that is deactivated by the administration of indomethacin. In addition, the untreated PH state was associated with significant activation of the contralateral posterior hypothalamus and contralateral ventral midbrain, which extended over the red nucleus and the substantia nigra.

INTERPRETATION

These activated subcortical structures may play a pivotal role in the pathophysiology of this syndrome.

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.

Efficacy of the 5-HT1A agonist, buspirone hydrochloride, in migraineurs with anxiety: a randomized, prospective, parallel group, double-blind, placebo-controlled study

OBJECTIVE

To examine the efficacy of buspirone, a 5-HT1A agonist, for migraine combined with anxiety disorder.

BACKGROUND

Modulation of the 5-hydroxytryptamine (5-HT) system is used for the neuropharmacology of migraine treatment; however, the involvement of the 5-HT1A system in migraine is not fully understood.

METHODS

Seventy-four outpatients aged 20 to 70 years (mean, 46.4; SD, 12.8) were analyzed. All subjects were diagnosed to have migraine according to the International Headache Society criteria and anxiety disorder according to DSM-IV. Subjects were randomly assigned to treatment with either buspirone (10 mg/day) or placebo for 6 weeks. Efficacy variables included changes in headache frequency, headache intensity, Hamilton Anxiety Rating Scale (HAM-A), Headache Self-Efficacy Scale (HMSE), and Headache Disability Inventory (HDI). The correlation between the headache improvement and the anxiolytic effect was analyzed.

RESULTS

Headache frequency showed a 43.3% reduction in the buspirone-treated group, but by only 10.3% in the placebo group. HAM-A and HDI were also significantly more lowered in buspirone-treated patients than in placebo-treated patients. However, headache intensity and HMSE score were unchanged. Correlation analysis of the relation between headache frequency reduction and HAM-A improvement, revealed no significant association.

CONCLUSIONS

In this study, buspirone showed a prophylactic effect in migraine with anxiety disorder, which was not secondary to its anxiolytic effect. This suggests that the agonistic action for 5-HT1A can be directly effective in migraine prophylaxis. However, more long-term study is warranted before concluding the efficacy.

Orbitofrontal cortex involvement in chronic analgesic-overuse headache evolving from episodic migraine

The way in which medication overuse transforms episodic migraine into chronic daily headache is unknown. To search for candidate brain areas involved in this process, we measured glucose metabolism with 18-FDG PET in 16 chronic migraineurs with analgesic overuse before and 3 weeks after medication withdrawal and compared the data with those of a control population (n = 68). Before withdrawal, the bilateral thalamus, orbitofrontal cortex (OFC), anterior cingulate gyrus, insula/ventral striatum and right inferior parietal lobule were hypometabolic, while the cerebellar vermis was hypermetabolic. All dysmetabolic areas recovered to almost normal glucose uptake after withdrawal of analgesics, except the OFC where a further metabolic decrease was found. A subanalysis showed that most of the orbitofrontal hypometabolism was due to eight patients overusing combination analgesics and/or an ergotamine-caffeine preparation. Medication overuse headache is thus associated with reversible metabolic changes in pain processing structures like other chronic pain disorders, but also with persistent orbitofrontal hypofunction. The latter is known to occur in drug dependence and could predispose subgroups of migraineurs to recurrent analgesic overuse.

Efficacy of Topiramate and Valproate in Chronic Migraine

OBJECTIVES

The aim of this study was to compare the efficacy of sodium valproate and topiramate in treating chronic migraine.

METHODS

Forty-nine patients with chronic migraine were randomly assigned to 1 of 2 groups of treatment: 750 mg/day valproate or 75 mg/day topiramate. Efficacy variables were number of days with headache over a 30-day period and changes in Migraine Disability Assessment (MIDAS) scores at 3 months.

RESULTS

At baseline the 2 groups had similar numbers of days with headache and mean MIDAS scores. At the end of the treatment period, a significant reduction in 30-day headache frequency with respect to baseline (P < 0.00001) and a significant reduction in MIDAS scores (P < 0.00001) were recorded in both groups. There were no significant differences in beneficial effects between the 2 drugs.

DISCUSSION

Valproate and topiramate seem to be able to manage successfully chronic migraine without substantial differences in efficacy and tolerability. This affords clear practical advantages-in the event of failure of or intolerance for one treatment, the patient may be switched to the other.

Functional brain imaging in hemicrania continua: implications for nosology and pathophysiology

Hemicrania continua is a strictly unilateral, continuous headache of mild to moderate intensity, with superimposed exacerbations of moderate to severe intensity that are accompanied by trigeminal autonomic features and migrainous symptoms. The syndrome is exquisitely responsive to indomethacin. Its clinical phenotype overlaps with that of the trigeminal autonomic cephalalgias and migraine, in which the hypothalamus and the brain stem, respectively, have been postulated to play central pathophysiologic roles. A recent positron-emission tomography study of a cohort of patients with hemicrania continua demonstrated significant activation of the contralateral posterior hypothalamus and ipsilateral dorsal rostral pons in association with the headache of hemicrania continua. In addition, there was activation of the ipsilateral ventrolateral midbrain, which extended over the red nucleus and the substantia nigra and bilateral pontomedullary junction. No intracranial vessel dilatation was obvious.

The association of brainstem lesions with migraine-like headache: an imaging study of multiple sclerosis

OBJECTIVE

To determine if the prevalence of migraine-like headache in patients with multiple sclerosis (MS) is associated with plaques in the brainstem or in other locations.

BACKGROUND

There is increasing evidence to suggest that periaqueductal gray matter (PAG) plays a role in the pathophysiology of migraine headache. There are a few clinical case studies and some experimental evidence in support of this observation.

METHODS

The study population of patients with demyelinating disease was identified by accessing the Department of Radiology magnetic resonance imaging (MRI) database accumulated between the years of December 1992 and June 2002. A total of 4369 MRI scan reports were available for review from that time period. Out of this, 1533 studies were reported to have possible demyelinating lesions. Medical records of these patients were reviewed to confirm the diagnosis of MS and also to document the headache complaints, if any. Two hundred and seventy-seven patients were identified with definite MS. A questionnaire was mailed to these patients to obtain additional details regarding MS and headache. The questionnaire response rate was 61% (169 of 277). This data were added to the information previously obtained from the medical records. The MRI films of each patient were examined, documenting location of the plaque, rather than the actual number. MRI and clinical data were kept separate until the final analysis. The International Headache Society criteria were used to classify headache types.

RESULTS

There were 207 female and 70 male patients available for analysis. Sixty-six percent (182 of 277) of patients were diagnosed with remitting-relapsing MS, 17% (47 of 277) with primary progressive MS, and 17% (48 of 277) with secondary progressive MS. Overall, 55.6% (154 of 277) of patients had a complaint of headache. Of these patients, 61.7% (95 of 154) met criteria for migraine-like headache, 25.3% (39 of 154) met criteria for tension-type headache, and 13% (20 of 154) had features of migraine and tension-type headache. MS patients with a plaque within the midbrain/periaqueductal gray matter areas had a four-fold increase in migraine-like headaches (odds ratio 3.91, 95% confidence interval 2.01 to 7.32; P < .0001), a 2.5-fold increase in tension-type headaches (odds ratio 2.58, 95% confidence interval 1.13 to 5.85; P= .02), and a 2.7-fold increase in combination of migraine and tension-type headaches (odds ratio 2.77, 95% confidence interval 0.98 to 7.82; P= .05) when compared to MS patients without a midbrain/periaqueductal gray matter lesion. Although not statistically significant, MS patients with three or more lesion locations were found to be approximately two times more likely to have migraine-like headaches compared to MS patients with 0 to 2 locations (3 to 5: odds ratio 2.47, 95% confidence interval 0.90 to 6.84; 6 to 8 locations: 1.82, 0.64 to 5.17; > or =9 locations: 2.41, 0.63 to 9.13). A linear trend was also observed between numbers of lesion locations and migraine-like headaches (P= .02).

CONCLUSION

The results of this study indicate that the presence of a midbrain plaque in patients with MS is associated with an increased likelihood of headache with migraine characteristics. (Headache 2005;45:670-677).

Can we Develop Neurally Acting Drugs for the Treatment of Migraine?

Serotonin (5-HT)(1B/1D) receptor agonists, which are also known as triptans, represent the most important advance in migraine therapeutics in the four millennia that the condition has been recognized. The vasoconstrictive activity of triptans produced a small clinical penalty in terms of coronary vasoconstriction but also raised an enormous intellectual question: to what extent is migraine a vascular problem? Functional neuroimaging and neurophysiological studies have consistently developed the theme of migraine as a brain disorder and, therefore, demanded that the search for neurally acting antimigraine drugs should be undertaken. The prospect of non-vasoconstrictor acute migraine therapies, potential targets for which are discussed here, offers a real opportunity to patients and provides a therapeutic rationale that places migraine firmly in the brain as a neurological problem, where it undoubtedly belongs.

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.

Migraine Pathophysiology

A combination of basic science and human physiology, particularly functional neuroimaging, has radically altered our understanding of migraine with a focus on brain mechanisms for this common and disabling disorder. Genetic studies have begun to provide plausible targets for the basic molecular defect in terms of ion channels, albeit thus far in the rare condition of familial hemiplegic migraine (FHM). Migraine pathophysiology involves the trigeminovascular system and central nervous system modulation of the pain-producing structures of the cranium. The degree to which head pain results from the activation of the nociceptors of pain-producing intracranial structures, or to the facilitation or lack of inhibition of afferent signals, is not clear at this time. An understanding of the pain mechanism is likely to provide insights into the mechanisms underlying the more generalized sensory dysfunction that is so typical of migraine.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computerized tomography, and functional magnetic resonance imaging, have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes, and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Posterior hypothalamic and brainstem activation in hemicrania continua

OBJECTIVE

To determine the brain structures involved in mediating the pain of hemicrania continua using positron emission tomography.

BACKGROUND

Hemicrania continua is a strictly unilateral, continuous headache of moderate intensity, with superimposed exacerbations of severe intensity that are accompanied by trigeminal autonomic features and migrainous symptoms. The syndrome is exquisitely responsive to indomethacin. Its clinical phenotype overlaps with that of the trigeminal autonomic headaches and migraine in which the hypothalamus and the brainstem, respectively, have been postulated to play central pathophysiologic roles. We hypothesized, based on the clinical phenotype, that hemicrania continua may involve activations in the hypothalamus, or dorsal rostral pons, or both.

METHODS

Seven patients with hemicrania continua were studied in two sessions each. In one session, the patients were scanned during baseline pain and when rendered completely pain free after being administered indomethacin 100 mg intramuscularly. In the other session, the patients were scanned during baseline pain and when still in pain after being administered placebo intramuscularly. Seven age- and sex-matched nonheadache subjects acted as the control group. The scan images were processed and analyzed using SPM99.

RESULTS

There was a significant activation of the contralateral posterior hypothalamus and ipsilateral dorsal rostral pons in association with the headache of hemicrania continua. In addition, there was activation of the ipsilateral ventrolateral midbrain, which extended over the red nucleus and the substantia nigra, and bilateral pontomedullary junction. No intracranial vessel dilatation was obvious.

CONCLUSIONS

This study demonstrated activations of various subcortical structures, in particular the posterior hypothalamus and the dorsal rostral pons. If posterior hypothalamic and brainstem activation are considered as markers of trigeminal autonomic headaches and migrainous syndromes, respectively, then the activation pattern demonstrated in hemicrania continua mirrors the clinical phenotype, with its overlap with trigeminal autonomic headaches and migraine.

Neurobiology in primary headaches

Primary headaches such as migraine and cluster headache are neurovascular disorders. Migraine is a painful, incapacitating disease that affects a large portion of the adult population with a substantial economic burden on society. The disorder is characterised by recurrent unilateral headaches, usually accompanied by nausea, vomiting, photophobia and/or phonophobia. A number of hypothesis have emerged to explain the specific causes of migraine. Current theories suggest that the initiation of a migraine attack involves a primary central nervous system (CNS) event. It has been suggested that a mutation in a calcium gene channel renders the individual more sensitive to environmental factors, resulting in a wave of cortical spreading depression when the attack is initiated. Genetically, migraine is a complex familial disorder in which the severity and the susceptibility of individuals are most likely governed by several genes that vary between families. Genom wide scans have been performed in migraine with susceptibility regions on several chromosomes some are associated with altered calcium channel function. With positron emission tomography (PET), a migraine active region has been pointed out in the brainstem. In cluster headache, PET studies have implicated a specific active locus in the posterior hypothalamus. Both migraine and cluster headache involve activation of the trigeminovascular system. In support, there is a clear association between the head pain and the release of the neuropeptide calcitonin gene-related peptide (CGRP) from the trigeminovascular system. In cluster headache there is, in addition, release of the parasympathetic neuropeptide vasoactive intestinal peptide (VIP) that is coupled to facial vasomotor symptoms. Triptan administration, activating the 5-HT(1B/1D) receptors, causes the headache to subside and the levels of neuropeptides to normalise, in part through presynaptic inhibition of the cranial sensory nerves. These data suggest a central role for sensory and parasympathetic mechanisms in the pathophysiology of primary headaches. The positive clinical trial with a CGRP receptor antagonist offers a new promising way of treatment.

Chronic cluster headache: New and emerging treatment options

Cluster headache (CH) is a primary headache syndrome characterized by short-lasting unilateral head pain attacks accompanied by ipsilateral oculofacial autonomic phenomena. Approximately 20% of CH patients have the chronic form and need continuous medical care. In the chronic form, attacks continue unabated for years, often on a daily basis, resulting in severe debilitation. It is a common experience that drug treatments are able to control or prevent the attacks in approximately 80% of chronic CH patients. In the remaining 20% of chronic cases, drugs are ineffective. Until recently, the etiology of CH was poorly understood and this hampered the development of new therapies. However, we have now gained a much improved understanding of the peripheral and central mechanisms giving rise to the pain in CH and this has inspired the development of new treatment approaches, which, although still in the initial phases of validation, appear to be very promising. Among these, the novel approach based on hypothalamic deep brain stimulation is one of the most promising.

Calcitonin gene-related peptide (CGRP) modulates nociceptive trigeminovascular transmission in the cat

Calcitonin gene-related peptide (CGRP) is released into the cranial circulation of humans during acute migraine. To determine whether CGRP is involved in neurotransmission in craniovascular nociceptive pathways, we microiontophoresed onto neurons in the trigeminocervical complex and intravenously administered the CGRP receptor antagonists alpha-CGRP-(8-37) and BIBN4096BS. Cats were anaesthetised with alpha-chloralose, and using halothane during surgical preparation. A craniotomy and C1/C2 laminectomy allowed access to the superior sagittal sinus (SSS) and recording site. Recordings of activity in the trigeminocervical complex evoked by electrical stimulation of the SSS were made. Multibarrelled micropipettes incorporating a recording electrode were used for microiontophoresis of test substances. Cells recorded received wide dynamic range (WDR) or nociceptive specific (NS) input from cutaneous receptive fields on the face or forepaws. Cell firing was increased to 25-30 Hz by microiontophoresis of L-glutamate (n = 43 cells). Microiontophoresis of alpha-CGRP excited seven of 17 tested neurons. BIBN4096BS inhibited the majority of units (26 of 38 cells) activated by l-glutamate, demonstrating a non-presynaptic site of action for CGRP. alpha-CGRP-(8-37) inhibited a similar proportion of units (five of nine cells). Intravenous BIBN4096BS resulted in a dose-dependent inhibition of trigeminocervical SSS-evoked activity (ED50 31 microg kg(-1)). The maximal effect observed within 30 min of administration. The data suggest that there are non-presynaptic CGRP receptors in the trigeminocervical complex that can be inhibited by CGRP receptor blockade and that a CGRP receptor antagonist would be effective in the acute treatment of migraine and cluster headache.

Steady-state visual evoked potentials and phase synchronization in migraine patients

We investigate phase synchronization in EEG recordings from migraine patients. We use the analytic signal technique, based on the Hilbert transform, and find that migraine brains are characterized by enhanced alpha band phase synchronization in the presence of visual stimuli. Our findings show that migraine patients have an overactive regulatory mechanism that renders them more sensitive to external stimuli.

[The trigeminovascular system in the human. Cerebral blood flow, functional imaging and primary headache]

Primary headache syndromes, such as cluster and migraine, are widely described as vascular headaches, even though there is considerable clinical evidence to suggest that both conditions are primarily central, that is regulated by the brain. The shared anatomical and physiological substrate for both clinical syndromes is the neural innervation of the cranial circulation. Early functional imaging using PET has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine and in the hypothalamic gray in cluster headache. These areas are involved in the pain process in a permissive or triggering manner rather than simply as a response to first-division nociceptive pain impulses. This article reviews findings in the physiology of the trigeminovascular system which demand renewed consideration of the neural influences in many primary headaches and the physiology of the neural innervation of cranial circulation. Primary headaches should thus be regarded as neurovascular headaches to emphasize the interaction between nerves and vessels which is their underlying characteristic.

Migraine Headache Misconceptions: Barriers to Effective Care

Migraine headaches affect 12% of the adult population in the United States and cause a significant economic loss due to decreased workplace productivity Although interactions between pharmacists and individuals with headache are common, few pharmacists receive adequate training regarding migraine therapy. We refute several misconceptions that hinder effective care, such as that migraine is a vascular disease, triptans cause rampant cardiacrelated morbidity and even mortality, a best oral triptan exists, sinus and tension headaches are prevalent, and migraine is a minor economic problem. Our pathophysiologic understanding demonstrates that migraine is a neurologic process of the trigeminovascular system, of which vascular effects are secondary. This process can result in a myriad of clinical signs and symptoms, often leading to a misdiagnosis of sinus or tension headache. The last decade's experience with triptans in more than half a billion people worldwide reveals a benign adverse-effect profile, particularly when taken early in an attack. Published reports and real-world experiences illustrate that these drugs do not merit fears of triptan-induced cardiac consequences in appropriately selected individuals. Society's productivity loss due to migraine is measured in billions of dollars. Restoring a patient's ability to function normally is now recognized as the primary treatment goal, not merely relieving pain. Thus, the overreliance on "pain killer" drugs such as butalbital-containing products and the continued underutilization of migraine-specific drugs need to be addressed. Opportunities exist for pharmacists and other health care providers to dispel continually propagated migraine misconceptions and familiarize themselves with advances in therapy. Such actions will benefit patients, the health care system, and society as a whole.

Effects of acute or chronic administration of anti-migraine drugs sumatriptan and zolmitriptan on serotonin synthesis in the rat brain

Triptans are 5-HT1 receptor agonists used as anti-migraine drugs. They act primarily on meningeal blood vessels and on trigeminovascular afferents, but they may also exert central effects. We studied the regional effects of acute and chronic treatment with sumatriptan or zolmitriptan on the rate of serotonin (5-HT) synthesis in the rat brain, using the alpha-14C-methyl-L-tryptophan quantitative autoradiographic method. Sumatriptan at low (300 microg/kg, s.c.) and high (1 mg/kg) doses, as well as zolmitriptan (100 microg/kg), acutely decreased (15-40%, P < 0.05-0.001) 5-HT synthetic rate in many brain regions, including the dorsal raphe nucleus. Chronically, sumatriptan (21 days, approximately 300 microg/kg per day via osmotic minipumps) induced significant increases in the 5-HT synthesis rate in many projection areas but had no effect in the dorsal raphe nucleus. The acute effects on 5-HT synthesis rate would be compatible with activation of 5-HT1 autoreceptors that inhibit serotonin release. In contrast, the increased 5-HT synthesis rate observed after chronic sumatriptan might possibly result from a down-regulation/desensitization of 5-HT1 receptors and/or unmasking of excitatory triptan-sensitive 5-HT receptors. Overall, the present findings indicate that not only zolmitriptan but also sumatriptan affect brain serotonergic neurotransmission.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computerized tomography, and functional magnetic resonance imaging, have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes, and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Migraine

Migraine is a very common neurobiological headache disorder that is caused by increased excitability of the CNS. It ranks among the world's most disabling medical illnesses. Diagnosis is based on the headache's characteristics and associated symptoms. The economic and societal effect of migraine is substantial: it affects patients' quality of life and impairs work, social activities, and family life. There are many acute and preventive migraine treatments. Acute treatment is either specific (triptans and ergots) or non-specific (analgesics). Disabling migraine should be treated with triptans. Increased headache frequency is an indication for preventive treatment. Preventive treatment decreases migraine frequency and improves quality of life. More treatments are being developed, which provides hope to the many patients whose migraines remain uncontrolled.

Activation of 5-HT1B/1D receptor in the periaqueductal gray inhibits nociception

It is considered that the site of action of the abortive antimigraine compounds acting at serotonin, 5-HT(1B/1D,) receptors (triptans) is the trigeminovascular system. We tested whether there is a non-trigeminal site of action. The 5-HT(1B/1D) agonist, naratriptan, was microinjected into the ventrolateral periaqueductal gray (vlPAG), and activity in the trigeminal nucleus caudalis (TNC) was monitored. Recordings were made from 20 nociceptive neurons in the dorsal horn of the TNC that received convergent input from the dura mater and face. Responses of neurons to dural, facial cutaneous and corneal stimulation were studied before and after injection of naratriptan. Naratriptan decreased the excitability to electrical stimulation of the dura mater as the A-fiber response decreased by 24 +/- 4.1% (p < 0.001) and the C-fiber response decreased by 42 +/- 8.2% (p < 0.001). Spontaneous activity was decreased by 38 +/- 7.5% (p < 0.001). After injection, the mechanical thresholds of the dura mater increased from (n = 14, p < 0.01). Responses to stimulation of the face and cornea were not altered by injection of naratriptan. These results suggest that 5-HT(1B/1D) receptor activation in the vlPAG activates descending pain-modulating pathways that inhibit dural, but not facial and corneal nociceptive input. These findings have implications for the understanding of the action of triptans in migraine and cluster headache, suggesting that brain loci other than the trigeminal nucleus may play a role in the clinical action of triptans.

Subcutaneous octreotide in cluster headache: Randomized placebo-controlled double-blind crossover study

Current practical evidence-based acute treatments of cluster headache are limited to subcutaneous and intranasal formulations of sumatriptan, and oxygen. Two small randomized, double-blind trials suggested efficacy of somatostatin in cluster headache. We sought to determine whether octreotide, a somatostatin analog, is effective in the abortive treatment of acute cluster headache. Patients with episodic and chronic cluster headache, as defined by the International Headache Society, were recruited to a double-blind placebo-controlled crossover study. Patients were instructed to treat two attacks of at least moderate pain severity, with at least a 24-hour break, using subcutaneous octreotide microg or matching placebo. The primary end point was the headache response defined as very severe, severe, or moderate pain becomes mild or nil, at 30 minutes. The primary end point was examined using a multilevel analysis approach. A total of 57 patients were recruited of whom 46 provided efficacy data on attacks treated with octreotide and 45 with placebo. The headache response rate with subcutaneous octreotide was 52%, whereas that with placebo was 36%. Modeling the treatment outcome as a binomial where response was determined by treatment, using the patient as the level 2 variable, and considering period effect, sex, and cluster headache type as other variables of interest, we found that the effect of subcutaneous octreotide 100 microg was significantly superior to placebo (p < 0.01). Subcutaneous octreotide 100 microg is effective in the acute treatment of cluster headache when compared with placebo. Nonvasconstrictor treatment of acute cluster headache is possible.

Management of trigeminal autonomic cephalgias and hemicrania continua

The trigeminal autonomic cephalgias (TACs) are a group of primary headache disorders characterised by unilateral trigeminal distribution pain that occurs in association with ipsilateral cranial autonomic features. This group of headache disorders includes cluster headache, paroxysmal hemicrania and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT syndrome). Although hemicrania continua has previously been classified amongst the TACs, its nosological status remains unclear. Despite their similarities, these disorders differ in their clinical manifestations and response to therapy, thus underpinning the importance of recognising them. We have outlined the clinical manifestations, differential diagnoses, diagnostic workup and the treatment options for each of these syndromes.

Migraine: an ophthalmologist's perspective

PURPOSE OF REVIEW

Migraine is a common disorder with visual and neurologic manifestations. Many patients present to ophthalmologists without a previous diagnosis of migraine. It is therefore essential for the ophthalmologist to have a good understanding of migraine to appropriately help these patients. Neurologic syndromes with migraine and retinopathy are well known. Here again, the ophthalmologist may play a role in establishing the correct diagnosis.

RECENT FINDINGS

For long the initial changes during a migraine attack have been shown to occur in the occipital cortex. In the recent years, the understanding of migraine has advanced with the availability of functional neuroimaging. A possible role of brainstem structures in the initiation of migraine attacks has been proposed based on functional magnetic resonance imaging blood oxygenation level-dependent signals. Activation of brainstem structures preceded activation of occipital cortex. Our understanding of cortical spreading depression is also advancing. Using multiwavelength optical intrinsic imaging, cortical spreading depression has been shown to have a triphasic response in rats. For the first time it has been shown that the cortical spreading depression activated the trigeminovascular system, which is followed by a series of cortical meningeal and brainstem events that cause the migraine headache. Sildenafil has been shown to induce migraine attack without dilation of cerebral blood vessels, further confirming that Wolf's vasogenic theory may not be true. Several loci for migraine have been identified in recent years. A new locus for migraine with and without aura has been identified on chromosome 6, a locus for migraine without aura to chromosome 14, and a locus for migraine with aura on chromosome 4.

SUMMARY

Our understanding of migraine is rapidly evolving with functional neuroimaging. There are several unanswered questions. In this article, we will review the epidemiology, genetics, and clinical features of various forms of migraine with emphasis on ocular migraine, pathogenesis, and briefly the management of migraine.

Therapeutic implications of the modular headache theory

A theoretical approach to understanding the primary headaches not yet classified by the International Headache Society classification system has been developed by the authors. It is proposed that groups of neurons, called modules, become activated to produce each symptom of a primary headache disorder and these modules are linked together to produce a headache. Headaches develop phenotypic stability through the process of learned stereotypy. This theory explains the huge diversity of headache phenomenology. It has implications for the classification, research and treatment of headache patients. The modular headache theory has therapeutic implications by directing us to focus on treatable modules and avoiding unnecessary treatment for less treatable symptoms. This allows for rational approaches to CNS hyperexcitability and incorporates the temporal patterns of modular activation into the patient's treatment plan.

Migraine: diagnosis and management

Migraine is the most common form of disabling primary headache and affects approximately 12% of studied Caucasian populations. Non-pharmacological management of migraine largely consists of lifestyle advice to help sufferers avoid situations in which attacks will be triggered. Preventive treatments for migraine should usually be considered on the basis of attack frequency, particularly its trend to change with time, and tract-ability to acute care. Acute care treatments for migraine can be divided into non-specific treatments (general analgesics, such as aspirin or non-steroidal anti--inflammatory drugs) and treatments relatively specific to migraine (ergotamine and the triptans). The triptans--sumatriptan, naratriptan, rizatriptan, zolmitriptan, almotriptan, eletriptan and frovatriptan--are potent serotonin, 5-HT1B/1D, receptor agonists which represent a major advance in the treatment of acute migraine. Chronic daily headache in association with analgesic overuse is probably the major avoidable cause of headache disability in the developed world.

Symptomatic migraine and sensitization of trigeminal nociception associated with contralateral pontine cavernoma

A 38-year-old woman is described with symptomatic strictly right-sided migraine associated with a pontine cavernoma affecting the contralateral (left) nucleus raphe magnus. A persistent facilitation of the right-sided trigeminal nociception was detected interictally using the 'nociception specific' blink reflex, which was more pronounced during the acute attack. This case shows for the first time, an impairment of the anti-nociceptive brainstem nuclei and the facilitation of the trigeminal nociception in the same subject, thus providing further evidence for the key role of the brainstem raphe nuclei in the pathophysiology of migraine.

Short-lasting unilateral neuralgiform headache with conjunctival injection and tearing syndrome: a review

The clinical features of short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome have been reviewed in 50 patients reported in the English language literature. SUNCT syndrome is a rare condition that predominates slightly in men. The mean age at onset is 50 years. It is characterized by strictly unilateral attacks centered on the orbital or periorbital regions, forehead, and temple. Generally, the pain is severe and neuralgic in character. The usual duration ranges from 5 to 250 seconds, although the reported range of duration is 2 seconds to 20 minutes. Ipsilateral conjunctival injection and lacrimation are present in most, but not all patients. Most patients are thought to have no refractory periods and this has probably been unreported in the past. Episodic and chronic forms of SUNCT exist. The attack frequency varies from less than one attack daily to more than 60 attacks per hour. The attacks are predominantly diurnal, although frequent nocturnal attacks can occur in some patients. A functional magnetic resonance imaging study in SUNCT syndrome has demonstrated ipsilateral hypothalamic activation. SUNCT was thought to be highly refractory to treatment. However, recent open-label trials of lamotrigine, gabapentin, topiramate, and intravenous lidocaine have produced beneficial therapeutic responses. These results offer the promise of better treatments for this syndrome, but require validation in controlled trials.

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.

Sustained-release niacin for prevention of migraine headache

Considerable advances in the diagnosis and treatment of migraine headache have occurred during the past decade, but treatment options for acute migraine attacks have expanded at a faster rate than those for prophylaxis. We describe a patient whose migraine headaches responded dramatically to sustained-release niacin as preventive treatment. Niacin is not generally considered to be effective for migraine prevention. However, low plasma levels of serotonin have been implicated in migraine pathogenesis, and niacin may act as a negative feedback regulator on the kynurenine pathway to shunt tryptophan into the serotonin pathway, thus increasing plasma serotonin levels. Sustained-release niacin merits further study as a potentially useful preventive therapy for migraine headache.

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.

Pathophysiology, epidemiology, and impact of migraine

Despite a decade of progress, migraine headache remains prevalent, disabling, underdiagnosed, and undertreated in the United States. Migraine affects approximately 12% of the population, and the economic burden in terms of annual cost of labor lost to migraine disability is between $5.6 and $17.2 billion. The threshold for migraine may be genetically determined, although recent genetic and neurophysiologic studies point to migraine as possibly a channelopathy. Cerebral cortical and brain stem changes occur in migraine. Head pain and associated symptoms of migraine can be explained by activation of the trigeminal vascular system. Evidence has also been accumulated that suggests the release of nitric oxide is an important trigger mechanism. Introduction of the triptans has dramatically advanced acute migraine pharmacotherapy, and preventive therapy has greatly improved; however, public health initiatives may be needed to further advance diagnosis and treatment of this common and disabling disorder.

Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT): Clinical Applications

Positron emission tomography and single-photon emission computed tomography are nuclear imaging modalities that excel in depicting the biological function of tissue. Unlike structural imaging methods, they provide functional diagnostic information about brain neoplasms, stroke, neurodegenerative disorders, epilepsy, cortical visual loss, and migraine.

Differing central amine receptor sensitivity in different migraine subtypes? A neuroendocrine study using buspirone

Despite the importance of the 5HT1A receptor in regulating central serotonergic tone, there is a dearth of research examining its role in migraine. In this study, we examined the hypothesis that there would be altered neuroendocrine responses to a 5HT1A agonist challenge in different migraine subtypes. Prolactin (PRL) responses to the 5HT1A receptor agonist drug buspirone were compared in 30 female subjects with migraine (ten migraine with aura, MA; ten migraine without aura, MO and ten chronic/transformed migraine, CM), and ten healthy controls matched for age, gender and menstrual status. None of the subjects were taking psychotropic medication or migraine prophylactic treatment and those with formal psychiatric disorder were excluded. Endocrine responses were determined by measuring differences between baseline PRL and maximum increases post-buspirone (deltaPRL). There was no difference in baseline PRL between groups. MA subjects did not differ in their PRL responses to buspirone compared to healthy controls. The MO group had a four-fold increase in mean deltaPRL responses compared to healthy controls. Mean deltaPRL was also increased in the CM group compared to controls, but the difference was less exaggerated. This study indicates that there is supersensitive central amine receptor function in MO and CM, but not in MA. These findings support the hypothesis that central 5HT function differs among the migraine subtypes. The results also suggest that migrainous 'transformation' may be associated with adaptive changes in central 5HT receptor sensitivity. The relative contribution of 'state' and 'trait' receptor function to these findings as well as the possible role of dopamine receptors is discussed.