Functional magnetic resonance imaging in episodic cluster headache

Pathophysiology of cluster headache: From the trigeminovascular system to the cerebral networks

BACKGROUND

Despite advances in neuroimaging and electrophysiology, cluster headache's pathogenesis remains unclear. This review will examine clinical neurophysiology studies, including electrophysiological and functional neuroimaging, to determine if they might help us construct a neurophysiological model of cluster headache.

RESULTS

Clinical, biochemical, and electrophysiological research have implicated the trigeminal-parasympathetic system in cluster headache pain generation, although the order in which these two systems are activated, which may be somewhat independent, is unknown. Electrophysiology and neuroimaging have found one or more central factors that may cause seasonal and circadian attacks. The well-known posterior hypothalamus, with its primary circadian pacemaker suprachiasmatic nucleus, the brainstem monoaminergic systems, the midbrain, with an emphasis on the dopaminergic system, especially when cluster headache is chronic, and the descending pain control systems appear to be involved. Functional connection investigations have verified electrophysiological evidence of functional changes in distant brain regions connecting to wide cerebral networks other than pain.

CONCLUSION

We propose that under the impact of external time, an inherited misalignment between the primary circadian pacemaker suprachiasmatic nucleus and other secondary extra- suprachiasmatic nucleus clocks may promote disturbance of the body's internal physiological clock, lowering the threshold for bout recurrence.

Involvement of the ipsilateral-to-the-pain anterior-superior hypothalamic subunit in chronic cluster headache

BACKGROUND

Despite hypothalamus has long being considered to be involved in the pathophysiology of cluster headache, the inconsistencies of previous neuroimaging studies and a limited understanding of the hypothalamic areas involved, impede a comprehensive interpretation of its involvement in this condition.

METHODS

We used an automated algorithm to extract hypothalamic subunit volumes from 105 cluster headache patients (57 chronic and 48 episodic) and 59 healthy individuals; after correcting the measures for the respective intracranial volumes, we performed the relevant comparisons employing logist regression models. Only for subunits that emerged as abnormal, we calculated their correlation with the years of illness and the number of headache attacks per day, and the effects of lithium treatment. As a post-hoc approach, using the 7 T resting-state fMRI dataset from the Human Connectome Project, we investigated whether the observed abnormal subunit, comprising the paraventricular nucleus and preoptic area, shows robust functional connectivity with the mesocorticolimbic system, which is known to be modulated by oxytocin neurons in the paraventricular nucleus and that is is abnormal in chronic cluster headache patients.

RESULTS

Patients with chronic (but not episodic) cluster headache, compared to control participants, present an increased volume of the anterior-superior hypothalamic subunit ipsilateral to the pain, which, remarkably, also correlates significantly with the number of daily attacks. The post-hoc approach showed that this hypothalamic area presents robust functional connectivity with the mesocorticolimbic system under physiological conditions. No evidence of the effects of lithium treatment on this abnormal subunit was found.

CONCLUSIONS

We identified the ipsilateral-to-the-pain antero-superior subunit, where the paraventricular nucleus and preoptic area are located, as the key hypothalamic region of the pathophysiology of chronic cluster headache. The significant correlation between the volume of this area and the number of daily attacks crucially reinforces this interpretation. The well-known roles of the paraventricular nucleus in coordinating autonomic and neuroendocrine flow in stress adaptation and modulation of trigeminovascular mechanisms offer important insights into the understanding of the pathophysiology of cluster headache.

CCH attack frequency reduction after psilocybin correlates with hypothalamic functional connectivity

OBJECTIVE

To evaluate the feasibility and prophylactic effect of psilocybin as well as its effects on hypothalamic functional connectivity (FC) in patients with chronic cluster headache (CCH).

BACKGROUND

CCH is an excruciating and difficult-to-treat disorder with incompletely understood pathophysiology, although hypothalamic dysfunction has been implicated. Psilocybin may have beneficial prophylactic effects, but clinical evidence is limited.

METHODS

In this small open-label clinical trial, 10 patients with CCH were included and maintained headache diaries for 10 weeks. Patients received three doses of peroral psilocybin (0.14 mg/kg) on the first day of weeks five, six, and seven. The first 4 weeks served as baseline and the last 4 weeks as follow-up. Hypothalamic FC was determined using functional magnetic resonance imaging the day before the first psilocybin dose and 1 week after the last dose.

RESULTS

The treatment was well tolerated. Attack frequency was reduced by mean (standard deviation) 31% (31) from baseline to follow-up (pFWER  = 0.008). One patient experienced 21 weeks of complete remission. Changes in hypothalamic-diencephalic FC correlated negatively with a percent change in attack frequency (pFWER  = 0.03, R = -0.81), implicating this neural pathway in treatment response.

CONCLUSION

Our results indicate that psilocybin may have prophylactic potential and implicates the hypothalamus in possible treatment response. Further clinical studies are warranted.

Altered functional connectivity of the thalamus and salience network in patients with cluster headache: a pilot study

BACKGROUND AND OBJECTIVE

Previous studies have shown that the salience network (SN) and the thalamus are involved in cluster headache (CH) attacks. However, very little is known regarding the altered thalamus-SN functional connectivity in CH. The aim of this study was to explore alterations of functional connectivity between the thalamus and the SN in patients with CH to further gain insight into the pathophysiology of CH.

MATERIALS AND METHODS

The resting-state functional MRI (rs-fMRI) data of 21 patients with CH in the headache attack remission state during in-bout periods and 21 age- and sex-matched normal controls were obtained. The rs-fMRI data were analyzed by the independent component analysis (ICA) method, and the thalamus-SN functional connectivity in patients with right-sided and left-sided CH was compared with that in normal controls.

RESULTS

Decreased functional connectivity was found between the thalamus, both ipsilateral and contralateral to the headache side, and the SN during headache remission state in both right-sided CH patients and left-sided CH patients.

CONCLUSIONS

The findings suggest that the decreased functional connectivity between the thalamus and SN might be one of the pathologies underpinning the CH. This helps us to understand better the nature of the brain dysfunction in CH and the basic pathologies of CH, which implies that this deserves further investigation.

Association of Clinical and Neuroanatomic Factors With Response to Ventral Tegmental Area DBS in Chronic Cluster Headache

BACKGROUND AND OBJECTIVES

Deep brain stimulation (DBS) of the ventral tegmental area (VTA) is a surgical treatment option for selected patients with refractory chronic cluster headache (CCH). We aimed to identify clinical and structural neuroimaging factors associated with response to VTA DBS in CCH.

METHODS

This prospective observational cohort study examines consecutive patients with refractory CCH treated with VTA DBS by a multidisciplinary team in a single tertiary neuroscience center as part of usual care. Headache diaries and validated questionnaires were completed at baseline and regular follow-up intervals. All patients underwent T1-weighted structural MRI before surgery. We compared clinical features using multivariable logistic regression and neuroanatomic differences using voxel-based morphometry (VBM) between responders and nonresponders.

RESULTS

Over a 10-year period, 43 patients (mean age 53 years, SD 11.9), including 29 male patients, with a mean duration of CCH 12 years (SD 7.4), were treated and followed up for at least 1 year (mean follow-up duration 5.6 years). Overall, there was a statistically significant improvement in median attack frequency from 140 to 56 per month (Z = -4.95, p < 0.001), attack severity from 10/10 to 8/10 (Z = -4.83, p < 0.001), and duration from 110 to 60 minutes (Z = -3.48, p < 0.001). Twenty-nine (67.4%) patients experienced ≥50% improvement in attack frequency and were therefore classed as responders. There were no serious adverse events. The most common side effects were discomfort or pain around the battery site (7 patients) and transient diplopia and/or oscillopsia (6 patients). There were no differences in demographics, headache characteristics, or comorbidities between responders and nonresponders. VBM identified increased neural density in nonresponders in several brain regions, including the orbitofrontal cortex, anterior cingulate cortex, anterior insula, and amygdala, which were statistically significant (p < 0.001).

DISCUSSION

VTA DBS showed no serious adverse events, and, although there was no placebo control, was effective in approximately two-thirds of patients at long-term follow-up. This study did not reveal any reliable clinical predictors of response. However, nonresponders had increased neural density in brain regions linked to processing of pain and autonomic function, both of which are prominent in the pathophysiology of CCH.

Brain regions involved in fractional amplitude of low-frequency fluctuation in cluster headache patients: a resting-state functional MRI study

BACKGROUND

We used resting-state functional magnetic resonance imaging (RS-fMRI) to assess the possible pathogenic role of fALFF in CH. A limited number of studies have reported on fractional amplitude of low-frequency fluctuation (fALFF) in cluster headache (CH).

METHODS

RS-fMRI scans of 23 patients with CH were obtained (11with left-sided headache and 12 with right-sided headache), along with scans of 23 age- and sex-matched normal controls. The RS-fMRI data were analyzed to explore abnormal brain activity in the left CH and right CH patients during the non-painful state in one cluster period. fALFF was compared between patients and controls, and correlation analysis between the regional mean fALFF values and clinical characteristics was performed.

RESULTS

A decrease in fALFF was detected in the left cerebellum, left lentiform nucleus, left frontal lobe, left anterior cingulate, and right postcentral gyrus in the left CH group compared to the controls, while a decrease of fALFF was detected in the right cerebellum, right cingulate gyrus, right superior parietal lobule, right inferior parietal lobule, right postcentral gyrus, and left precuneus in the right CH group. No patient had a region with increased fALFF. A moderate correlation was observed between some regional mean fALFF values and the clinical characteristics.

CONCLUSIONS

We deduced that dysfunction in multiple brain areas is involved in the non-painful state of CH during a cluster period.

Anatomy and Physiology of Headache

Headache disorders can produce recurrent, incapacitating pain. Migraine and cluster headache are notable for their ability to produce significant disability. The anatomy and physiology of headache disorders is fundamental to evolving treatment approaches and research priorities. Key concepts in headache mechanisms include activation and sensitization of trigeminovascular, brainstem, thalamic, and hypothalamic neurons; modulation of cortical brain regions; and activation of descending pain circuits. This review will examine the relevant anatomy of the trigeminal, brainstem, subcortical, and cortical brain regions and concepts related to the pathophysiology of migraine and cluster headache disorders.

Cluster headache pathophysiology: What we have learned from advanced neuroimaging

Background

Although remarkable progress has been achieved in understanding cluster headache (CH) pathophysiology, there are still several gaps about the mechanisms through which independent subcortical and cortical brain structures interact with each other. These gaps could be partially elucidated by structural and functional advanced neuroimaging investigations.

Objective

Although we are aware that substantial achievements have come from preclinical, neurophysiological, and biochemical experiments, the present narrative review aims to summarize the most significant findings from structural, microstructural, and functional neuroimaging investigations, as well as the consequent progresses in understanding CH pathophysiological mechanisms, to achieve a comprehensive and unifying model.

Results

Advanced neuroimaging techniques have contributed to overcoming the peripheral hypothesis that CH is of cavernous sinus pathology, in transitioning from the pure vascular hypothesis to a more comprehensive trigeminovascular model, and, above all, in clarifying the role of the hypothalamus and its connections in the genesis of CH.

Conclusion

Altogether, neuroimaging findings strongly suggest that, beyond the theoretical model of the “pain matrix,” the model of the “neurolimbic pain network” that is accepted in migraine research could also be extended to CH. Indeed, although the hypothalamus’ role is undeniable, the genesis of CH attacks is complex and seems to not be just the result of a single “generator.” Cortical‐hypothalamic‐brainstem functional interconnections that can switch between out‐of‐bout and in‐bout periods, igniting the trigeminovascular system (probably by means of top‐down mechanisms) and the consensual trigeminal autonomic reflexes, may represent the “neuronal background” of CH.

Areas of cerebral blood flow changes on arterial spin labelling with the use of symmetric template during nitroglycerin triggered cluster headache attacks

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Cluster headache is a severe unilateral primary headache disorder; however, the brain is asymmetric, therefore using a symmetric template before flipping in the x-axis allows for ipsilateral analysis of attacks without loss of coherence across the group.

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Increases in cerebral blood flow beyond pain anticipation, processing and modulation areas, including hypothalamic regions and ipsilateral pons, have a crucial pathophysiological role in cluster headache attacks.

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The pain experienced during cluster headache attacks is so severe that it “switches off” areas involved in the default brain network.

Background

Cluster headache is a rare, strictly unilateral, severe episodic primary headache disorder. Due to the unpredictable and episodic nature of the attacks, nitroglycerin has been used to trigger attacks for research purposes to further our understanding of cluster headache pathophysiology.

Objectives

We aimed to identify regions of significant cerebral blood flow (CBF) changes during nitroglycerin triggered cluster headache attacks, using MRI with arterial spin labelling (ASL).

Methods

Thirty-three subjects aged 18–60 years with episodic and chronic cluster headache were recruited and attended an open clinical screening visit without scanning to receive an intravenous nitroglycerin infusion (0.5 μg/kg/min over 20 min). Those for whom nitroglycerin successfully triggered a cluster headache attack, were invited to attend two subsequent scanning visits. They received either single-blinded intravenous nitroglycerin (0.5 μg/kg/min) or an equivalent volume of single-blinded intravenous 0.9% sodium chloride over a 20-minute infusion. Whole-brain CBF maps were acquired using a 3 Tesla MRI scanner pre-infusion and post-infusion. As cluster headache is a rare condition and purely unilateral disorder, an analysis strategy to ensure all the image data corresponded to symptomatology in the same hemisphere, without losing coherence across the group, was adopted. This consisted of spatially normalising all CBF maps to a standard symmetric reference template before flipping the images about the anterior-posterior axis for those CBF maps of subjects who experienced their headache in the right hemisphere. This procedure has been employed in previous studies and generated a group data set with expected features on the left hemisphere only.

Results

Twenty-two subjects successfully responded to the nitroglycerin infusion and experienced triggered cluster headache attacks. A total of 20 subjects completed the placebo scanning visit, 20 completed the nitroglycerin scanning visit, and 18 subjects had completed both the nitroglycerin and placebo scanning visits. In a whole-brain analysis, we identified regions of significantly elevated CBF in the medial frontal gyrus, superior frontal gyrus, inferior frontal gyrus and cingulate gyrus, ipsilateral to attack side, in CBF maps acquired during cluster headache attack; compared with data from the placebo session. We also identified significantly reduced CBF in the precuneus, cuneus, superior parietal lobe and occipital lobe contralateral to the attack side. Of particular interest to this field of investigation, both the hypothalamus and ipsilateral ventral pons showed higher CBF in a separate region of interest analysis.

Conclusion

Our data demonstrate that severe cluster headache leads to significant increases in regional cerebral perfusion, likely to reflect changes in neuronal activity in several regions of the brain, including the hypothalamus and the ventral pons. These data contribute to our understanding of cluster headache pathophysiology; and suggest that non-invasive ASL technology may be valuable in future mechanistic studies of this debilitating condition.

Diagnostic protocols and newer treatment modalities for cluster headache

Cluster Headaches are one of the most arguably severe forms of primary headache syndrome that affects humans. Although it is relatively uncommon, it has a significant impact on the quality of life. It is a multifactorial disease that has risk factors ranging from seasonal changes, lifestyle habits to genetics. It occurs in 2 forms- Episodic and Chronic, each having its well-defined Diagnostic Criteria. Moreover, Cluster Headache has an exhaustive list of options for both Preventive and Abortive treatment. This article focuses on Cluster Headache, its pathophysiology, risk factors, differentials, and its diverse treatment modalities. In this study, an all-language literature search was conducted on Medline, Cochrane, Embase, and Google Scholar till October 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: "Cluster Headache," "Triptans," "Neuromodulation," and "Migraine." We explored the literature on Cluster Headache for its epidemiology, pathophysiology, the role of various genes and how they bring about the disease as well as its episodic and chronic variants, and treatment options. Although we have a wide variety of options for Preventive and Abortive therapy, newer more effective pharmacological and non-pharmacological interventions are being developed, and must be integrated into new treatment protocols.

[Trigeminal autonomic cephalgias: features of diagnosis and treatment]

Trigeminal autonomic cephalgias is a group of primary headaches, including cluster headache, paroxysmal hemicrania and hemicrania continua, as well as two forms of short- lasting unilateral neuralgiform headache attacks, the complexity of diagnosis of which is determined by the low prevalence and some similarity of clinical manifestations both among themselves and with other diseases in particular with migraine and trigeminal neuralgia. Despite the rather short duration of headache attacks, the intensity of the pain syndrome reaches a severe and very severe degree, and the high frequency of paroxysms per day significantly complicates abortion treatment and leads to a pronounced professional and social maladjustment. At the same time, the possibility of using effective specific prophylactic therapy determines the importance of accurate diagnosis and, therefore, the knowledge of neurologists on this issue.

Cluster Headache Pathophysiology—A Disorder of Network Excitability?

Patients’ accounts of cluster headache attacks, ictal restlessness, and electrophysiological studies suggest that the pathophysiology involves Aδ-fibre nociceptors and the network processing their input. Continuous activity of the trigeminal autonomic reflex throughout the in-bout period results in central sensitization of these networks in many patients. It is likely that several factors force circadian rhythmicity upon the disease. In addition to sensitization, circadian changes in pain perception and autonomic innervation might influence the excitability of the trigeminal cervical complex. Summation of several factors influencing pain perception might render neurons vulnerable to spontaneous depolarization, particularly at the beginning of rapid drops of the pain threshold (“summation headache”). In light of studies suggesting an impairment of short-term synaptic plasticity in CH patients, we suggest that the physiologic basis of CH attacks might be network overactivity—similarly to epileptic seizures. Case reports documenting cluster-like attacks support the idea of distinct factors being transiently able to induce attacks and being relevant in the pathophysiology of the disorder. A sustained and recurring proneness to attacks likely requires changes in the activity of other structures among which the hypothalamus is the most probable candidate.

Essential oils and cluster headache: insights from two cases

Essential oils with proconvulsive properties are known to cause seizures and may worsen migraine. Here, we report two cases of cluster headache temporally related to the use of toothpastes containing essential oils of camphor and eucalyptus.

The neurobiology of cluster headache

Cluster headache is a primary headache form occurring in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in periods lasting 1-2months, the cluster periods. A genetic component is suggested by the familial occurrence of the disease but a genetic linkage is yet to be identified. Contemporary activation of trigeminal and cranial parasympathetic systems-the so-called trigemino-parasympathetic reflex-during the headache attacks seem to cause the pain and accompanying oculo-facial autonomic phenomena respectively. At peripheral level, the increased calcitonin gene related peptide (CGRP) plasma levels suggests trigeminal system activation during cluster headache attacks. The temporal pattern of the disease both in terms of circadian rhythmicity and seasonal recurrence has suggested involvement of the hypothalamic biological clock in the pathophysiology of cluster headache. The posterior hypothalamus was investigate as the cluster generator leading to activation of the trigemino-parasympathetic reflex, but the accumulated experience after 20 years of hypothalamic electrical stimulation to treat the condition indicate that this brain region rather acts as pain modulator. Efficacy of monoclonal antibodies to treat episodic cluster headache points to a key role of CGRP in the pathophysiology of the condition.

Cluster Headache: What's New?

Background

Cluster headache is a highly disabling primary headache disorder which is widely described as the most painful condition a human can experience.

Aim

To provide an overview of the clinical characteristics, epidemiology, risk factors, differential diagnosis, pathophysiology and treatment options of cluster headache, with a focus on recent developments in the field.

Methods

Structured review of the literature on cluster headache.

Results

Cluster headache affects approximately one in 1000 of the population. It is characterised by attacks of severe unilateral head pain associated with ipsilateral cranial autonomic symptoms, and the tendency for attacks to occur with circadian and circannual periodicity. The pathophysiology of cluster headache and other primary headache disorders has recently become better understood and is thought to involve the hypothalamus and trigeminovascular system. There is good quality evidence for acute treatment of attacks with parenteral triptans and high flow oxygen; preventive treatment with verapamil; and transitional treatment with oral corticosteroids or greater occipital nerve injection. New pharmacological and neuromodulation therapies have recently been developed.

Conclusion

Cluster headache causes distinctive symptoms, which once they are recognised can usually be managed with a variety of established treatments. Recent pathophysiological understanding has led to the development of newer pharmacological and neuromodulation therapies, which may soon become established in clinical practice.

Role of Functional Neuroimaging in Primary Headache Disorders

Background

Key structures for the pathophysiology of primary headache disorders such as migraine, cluster headache, and other trigeminal autonomic cephalalgias were identified by imaging in the past years.

Objective

Available data on functional imaging in primary headache disorders are summarized in this review.

Material and Methods

We performed a MEDLINE search on December 27^th, 2020 using the search terms "primary headache" AND "imaging" that returned 453 results in English, out of which 137 were labeled reviews. All articles were evaluated for content and relevance for this narrative review.

Results

The structure depicted most consistently using functional imaging in different states of primary headaches (without and with pain) was the posterior hypothalamus. Whole-brain imaging techniques such as resting-state functional resonance imaging showed a wide-ranging association of cortical and subcortical areas with human nociceptive processing in the pathophysiological mechanisms underlying the different TACs. Similarities of distinct groups of primary headache disorders, as well as their differences in brain activation across these disorders, were highlighted.

Conclusion

The importance of neuroimaging research from clinical practice point of view remains the reliable and objective distinction of each individual pain syndrome from one another. This will help to make the correct clinical diagnosis and pave the way for better and effective treatment in the future. More research will be necessary to fulfill this unmet need.

Chronic Cluster Headache Update and East-West Comparisons: Focusing on Clinical Features, Pathophysiology, and Management

PURPOSE OF REVIEW

This review provides an update on chronic cluster headache (CH) focusing on clinical features, pathophysiology, and management as well as comparisons between Eastern and Western populations.

RECENT FINDINGS

Chronic CH in Eastern populations was relatively rare, compared to that in Western populations. Lacrimation and/or conjunctival injection is the most frequently reported cranial autonomic symptom, and visual aura is predominant in chronic CH patients. Neuroimaging evidence in both ethnic groups suggests that CH pathophysiology involves the hypothalamus and pain-modulatory areas, with dynamic alternations between CH episodes. Recent evidence indicates that midbrain dopaminergic systems may participate in CH chronicity. Noteworthy advances have emerged in neuromodulatory therapies for chronic CH, but treatment with calcitonin gene-related peptide (CGRP) monoclonal antibodies has been unsuccessful. Recent evidence shows divergence of chronic CH between Eastern and Western populations. Neuromodulatory therapies but not CGRP inhibition is effective in this intractable patient group.

Understanding Cluster Headache Using Magnetic Resonance Imaging

Cluster headache is an excruciating pain syndrome characterized by unilateral head pain attacks, lasting between 15 and 180 min, accompanied by marked ipsilateral cranial autonomic symptoms, such as lacrimation and conjunctival injection. Despite important insights provided by neuroimaging studies and deep brain stimulation findings, the pathophysiology of cluster headache and its pathways of chronicization are still elusive. In this mini-review, we will provide an overview of the functional and structural neuroimaging studies in episodic and chronic cluster headache conditions conducted to clarify the underlying pathophysiology.

Phase dependent hypothalamic activation following trigeminal input in cluster headache

BACKGROUND

Task-free imaging approaches using PET have shown the posterior hypothalamus to be specifically activated during but not outside cluster headache attacks. Evidence from task related functional imaging approaches however is scarce.

METHODS

Twenty-one inactive cluster headache patients (episodic cluster headache out of bout), 16 active cluster headache patients (10 episodic cluster headache in bout, 6 chronic cluster headache) and 18 control participants underwent high resolution brainstem functional magnetic resonance imaging of trigeminal nociception using gaseous ammonia as a painful stimulus.

RESULTS

Following trigeminonociceptive stimulation with ammonia there was a significantly stronger activation within the posterior hypothalamus in episodic cluster headache patients out of bout when compared to controls. When contrasting estimates of the pain contrast, active cluster headache patients where in between the two other groups but did not differ significantly from either.

CONCLUSION

The posterior hypothalamus might thus be hyperexcitable in cluster headache patients outside the bout while excitability to external nociceptive stimuli decreases during in bout periods, probably due to frequent hypothalamic activation and possible neurotransmitter exhaustion during cluster attacks.

Altered Hypothalamic Region Covariance in Migraine and Cluster Headache: A Structural MRI Study

OBJECTIVES

The hypothalamus plays a key role in both migraine and cluster headache (CH). As brain region-to-region structural correlations are believed to reflect structural and functional brain connectivity patterns, we assessed the structural covariance patterns between the volume of the hypothalamic region and vertex-by-vertex measurements of cortical thickness in patients with migraine and in those with CH relative to healthy controls (HC).

METHODS

T1-weighted images were acquired on a 3T MRI scanner for a total of 59 subjects including 18 patients with CH (age: mean = 43.8, SD = 12.4), 19 with migraine (age: mean = 40.1, SD = 12.2), and 22 HCs (age: mean = 39.1, SD = 8.2). Imaging was collected between attacks (migraineurs) and during out-of-bout phases (CH). Data were post-processed using FreeSurfer version 6.0 and within-group correlations between hypothalamic region volume with cortical thickness were explored using a whole-brain vertex-wise linear model approach. Between-group differences in correlation slopes between hypothalamic region volume and vertex-by-vertex measurements of cortical thickness were interrogated using post-hoc comparisons.

RESULTS

There were no significant between-group differences (migraine vs CH; migraine vs HC; or CH vs HC) for age, sex, total brain volume or volume of the left or right hypothalamic region. For each group, there were significant positive correlations (P < .01) between right and left hypothalamic region volumes with cortical thickness measurements. HC had significant positive correlations between hypothalamic region volume and cortical thickness over large portions of the superior and rostral medial frontal, orbitofrontal cortex and rostral anterior cingulate, and smaller clusters in the superior and middle temporal, posterior cingulate, fusiform, and precentral cortex. Post-hoc analysis showed significant differences in covariance patterns in those with migraine and CH relative to HC, with both migraine patients and CH having weaker structural covariance of hypothalamic region volume with frontal and temporal cortical thickness.

CONCLUSION

Recent evidence suggests hypothalamic region connectivity to frontal and temporal areas to be relevant for regulating pain perception. Thus, the diminished structural covariance in migraineurs and CH might suggest abnormal functioning of the pain control circuitry and contribute to mechanisms underlying central sensitization and chronification of pain.

The biological clock in cluster headache: A review and hypothesis

Objective

To review and discuss the putative role of light, sleep, and the biological clock in cluster headache.

Discussion

Cluster headache attacks are believed to be modulated in the hypothalamus; moreover, the severe pain and typical autonomic cranial features associated with cluster headache are caused by abnormal activity of the trigeminal-autonomic reflex. The temporal pattern of cluster headache attacks suggests involvement of the biological clock, and the seasonal pattern is influenced by the number of daylight hours. Although sleep is often reported as a trigger for cluster headache attacks, to date no clear correlation has been established between these attacks and sleep stage.

Conclusions

We hypothesize that light, sleep, and the biological clock can change the brain’s state, thereby lowering the threshold for activating the trigeminal-autonomic reflex, resulting in a cluster headache attack. Understanding the mechanisms that contribute to the daily and seasonal fluctuations in cluster headache attacks may provide new therapeutic targets.

Update on the pathophysiology of cluster headache: imaging and neuropeptide studies

OBJECTIVE

Cluster headache (CH) is the most severe primary headache condition. Its pathophysiology is multifaceted and incompletely understood. This review brings together the latest neuroimaging and neuropeptide evidence on the pathophysiology of CH.

METHODS

A review of the literature was conducted by searching PubMed and Web of Science. The search was conducted using the following keywords: imaging studies, voxel-based morphometry, diffusion-tensor imaging, diffusion magnetic resonance imaging, tractography, connectivity, cerebral networks, neuromodulation, central modulation, deep brain stimulation, orexin-A, orexin-B, tract-based spatial statistics, single-photon emission computer tomography studies, positron-emission tomography, functional magnetic resonance imaging, magnetic resonance spectroscopy, trigeminovascular system, neuropeptides, calcitonin gene-related peptide, neurokinin A, substance P, nitric oxide synthase, pituitary adenylate cyclase-activating peptide, vasoactive intestinal peptide, neuropeptide Y, acetylcholine, noradrenaline, and ATP. "Cluster headache" was combined with each keyword for more relevant results. All irrelevant and duplicated records were excluded. Search dates were from October 1976 to May 2018.

RESULTS

Neuroimaging studies support the role of the hypothalamus in CH, as well as other brain areas involved in the pain matrix. Activation of the trigeminovascular system and the release of neuropeptides play an important role in CH pathophysiology. Among neuropeptides, calcitonin gene-related peptide, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide have been reported to be reliable biomarkers for CH attacks, though not specific for CH. Several other neuropeptides are involved in trigeminovascular activation, but the current evidence does not qualify them as reliable biomarkers in CH.

CONCLUSION

CH has a complex pathophysiology and the pain mechanism is not completely understood. Recent neuroimaging studies have provided insight into the functional and structural network bases of CH pathophysiology. Although there has been important progress in neuropeptide studies, a specific biomarker for CH is yet to be found.

Functional Neuroimaging in Trigeminal Autonomic Cephalalgias

Functional neuroimaging was able to identify key structures for the pathophysiology of trigeminal autonomic cephalalgias (TACs) including cluster headache, paroxysmal hemicrania, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing or cranial autonomic features and hemicrania continua. The posterior hypothalamus was the structure most consistently depicted with functional imaging in different states of disease with and without pain. Network-oriented imaging techniques such as resting-state functional resonance imaging were able to show a broader involvement of human trigeminal pain processing in the underlying pathophysiological mechanisms of the different TACs, highlighting similarities between this distinct group of primary headache disorders, while also demonstrating the differences in brain activation across these disorders. The most important clinical assignment for neuroimaging research from the treating physician remains the objective and reliable distinction of each individual TAC syndrome from one another, to make the correct clinical diagnosis as the foundation for proper treatment. More research will be necessary to fulfill this unmet need.

Cluster Headache: Epidemiology, Pathophysiology, Clinical Features, and Diagnosis

Cluster headache is a primary headache disorder affecting up to 0.1% of the population. Patients suffer from cluster headache attacks lasting from 15 to 180 min up to 8 times a day. The attacks are characterized by the severe unilateral pain mainly in the first division of the trigeminal nerve, with associated prominent unilateral cranial autonomic symptoms and a sense of agitation and restlessness during the attacks. The male-to-female ratio is approximately 2.5:1. Experimental, clinical, and neuroimaging studies have advanced our understanding of the pathogenesis of cluster headache. The pathophysiology involves activation of the trigeminovascular complex and the trigeminal-autonomic reflex and accounts for the unilateral severe headache, the prominent ipsilateral cranial autonomic symptoms. In addition, the circadian and circannual rhythmicity unique to this condition is postulated to involve the hypothalamus and suprachiasmatic nucleus. Although the clinical features are distinct, it may be misdiagnosed, with patients often presenting to the otolaryngologist or dentist with symptoms. The prognosis of cluster headache remains difficult to predict. Patients with episodic cluster headache can shift to chronic cluster headache and vice versa. Longitudinally, cluster headache tends to remit with age with less frequent bouts and more prolonged periods of remission in between bouts.

Therapeutic Approaches for the Management of Trigeminal Autonomic Cephalalgias

Trigeminal autonomic cephalalgia (TAC) encompasses 4 unique primary headache types: cluster headache, paroxysmal hemicrania, hemicrania continua, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms. They are grouped on the basis of their shared clinical features of unilateral headache of varying durations and ipsilateral cranial autonomic symptoms. The shared clinical features reflect the underlying activation of the trigeminal-autonomic reflex. The treatment for TACs has been limited and not specific to the underlying pathogenesis. There is a proportion of patients who are refractory or intolerant to the current standard medical treatment. From instrumental bench work research and neuroimaging studies, there are new therapeutic targets identified in TACs. Treatment has become more targeted and aimed towards the pathogenesis of the conditions. The therapeutic targets range from the macroscopic and structural level down to the molecular and receptor level. The structural targets for surgical and noninvasive neuromodulation include central neuromodulation targets: posterior hypothalamus and, high cervical nerves, and peripheral neuromodulation targets: occipital nerves, sphenopalatine ganglion, and vagus nerve. In this review, we will also discuss the neuropeptide and molecular targets, in particular, calcitonin gene-related peptide, somatostatin, transient receptor potential vanilloid-1 receptor, nitric oxide, melatonin, orexin, pituitary adenylate cyclase-activating polypeptide, and glutamate.

Defective functional connectivity between posterior hypothalamus and regions of the diencephalic-mesencephalic junction in chronic cluster headache

OBJECTIVE

We tested the hypothesis of a defective functional connectivity between the posterior hypothalamus and diencephalic-mesencephalic regions in chronic cluster headache based on: a) clinical and neuro-endocrinological findings in cluster headache patients; b) neuroimaging findings during cluster headache attacks; c) neuroimaging findings in drug-refractory chronic cluster headache patients improved after successful deep brain stimulation.

METHODS

Resting state functional magnetic resonance imaging, associated with a seed-based approach, was employed to investigate the functional connectivity of the posterior hypothalamus in chronic cluster headache patients (n = 17) compared to age and sex-matched healthy subjects (n = 16). Random-effect analyses were performed to study differences between patients and controls in ipsilateral and contralateral-to-the-pain posterior hypothalamus functional connectivity.

RESULTS

Cluster headache patients showed an increased functional connectivity between the ipsilateral posterior hypothalamus and a number of diencephalic-mesencephalic structures, comprising ventral tegmental area, dorsal nuclei of raphe, and bilateral substantia nigra, sub-thalamic nucleus, and red nucleus ( p < 0.005 FDR-corrected vs . control group). No difference between patients and controls was found comparing the contralateral hypothalami.

CONCLUSIONS

The observed deranged functional connectivity between the posterior ipsilateral hypothalamus and diencephalic-mesencephalic regions in chronic cluster headache patients mainly involves structures that are part of (i.e. ventral tegmental area, substantia nigra) or modulate (dorsal nuclei of raphe, sub-thalamic nucleus) the midbrain dopaminergic systems. The midbrain dopaminergic systems could play a role in cluster headache pathophysiology and in particular in the chronicization process. Future studies are needed to better clarify if this finding is specific to cluster headache or if it represents an unspecific response to chronic pain.

Overview of Trigeminal Autonomic Cephalalgias: Nosologic Evolution, Diagnosis, and Management

The term trigeminal autonomic cephalalgias (TACs) encompasses four primary headache disorders – cluster headache, paroxysmal hemicrania (PH), hemicrania continua (HC), short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT)/short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA). All of these except HC are characterized by short-lasting headaches. HC is characterized by a continuous unilateral headache that waxes and wanes in its intensity without complete resolution. It is included in the TACs group given the overlap in the activation of the posterior hypothalamic grey, and the shared clinical feature of unilateral head pain with ipsilateral cranial autonomic symptoms. The present review gives an overview of the nosologic evolution, diagnosis, and management of TACs.

Optimal deep brain stimulation site and target connectivity for chronic cluster headache

OBJECTIVE

To investigate the mechanism of action of deep brain stimulation for refractory chronic cluster headache and the optimal target within the ventral tegmental area.

METHODS

Seven patients with refractory chronic cluster headache underwent high spatial and angular resolution diffusion MRI preoperatively. MRI-guided and MRI-verified electrode implantation was performed unilaterally in 5 patients and bilaterally in 2. Volumes of tissue activation were generated around active lead contacts with a finite-element model. Twelve months after surgery, voxel-based morphometry was used to identify voxels associated with higher reduction in headache load. Probabilistic tractography was used to identify the brain connectivity of the activation volumes in responders, defined as patients with a reduction of ≥30% in headache load.

RESULTS

There was no surgical morbidity. Average follow-up was 34 ± 14 months. Patients showed reductions of 76 ± 33% in headache load, 46 ± 41% in attack severity, 58 ± 41% in headache frequency, and 51 ± 46% in attack duration at the last follow-up. Six patients responded to treatment. Greatest reduction in headache load was associated with activation in an area cantered at 6 mm lateral, 2 mm posterior, and 1 mm inferior to the midcommissural point of the third ventricle. Average responders' activation volume lay on the trigeminohypothalamic tract, connecting the trigeminal system and other brainstem nuclei associated with nociception and pain modulation with the hypothalamus, and the prefrontal and mesial temporal areas.

CONCLUSIONS

We identify the optimal stimulation site and structural connectivity of the deep brain stimulation target for cluster headache, explicating possible mechanisms of action and disease pathophysiology.

The pathophysiology of episodic cluster headache: Insights from recent neuroimaging research

Background

Cluster headache is a disorder characterized by intermittent, severe unilateral head pain accompanied by cranial autonomic symptoms. Most cases of CH are episodic, manifesting as “in-bout” periods of frequent headache separated by month-to-year-long “out-of-bout” periods of remission. Previous imaging studies have implicated the hypothalamus and pain matrix in the pathogenesis of episodic CH. However, the pathophysiology driving the transition between in- and out-of-bout periods remains unclear.

Methods

The present study provides a narrative review of previous neuroimaging studies on the pathophysiology of episodic CH, addressing alterations in brain structures, metabolism, and structural and functional connectivity occurring between bout periods.

Results

Although the precise brain structures responsible for episodic CH are unknown, major roles are indicated for the posterior hypothalamus (especially in acute attacks), the pain neuromatrix with an emphasis on central descending pain modulation, and non-traditional pain processing networks including the occipital, cerebellar, and salience networks. These areas are potentially related to dynamic transitioning between in- and out-of-bout periods.

Conclusion

Recent progress in magnetic resonance imaging of episodic CH has provided additional insights into dynamic bout-associated structural and functional connectivity changes in the brain, especially in non-traditional pain processing network areas. These areas warrant future investigations as targets for neuromodulation in patients with CH.

Post-Operative Cluster Headache Following Carotid Endarterectomy

BACKGROUND

Secondary cluster headache following carotid endarterectomy (CEA) is a rare condition and may help us understand the pathophysiology of primary cluster headache.

SUMMARY

We describe 2 patients diagnosed with cluster headache, fulfilling the ICHD-IIIB criteria, following CEA. Neither of the patients had headache prior to surgery. They both responded to treatment with oxygen and verapamil. Recent medical literature does not describe any definite cases of cluster headache following CEA. Cluster-like headache has been reported in several studies in the 1990s. Recent studies in primary cluster headache patients show evidence for a central origin of cluster headache in which no peripheral drive seems necessary. Key Messages: Our findings may provide more insight into the pathophysiology and show how a peripheral cause may lead to cluster headache. We hypothesize a role of the trigemino-autonomic reflex. Damage to the carotid artery may activate this reflex and trigger cluster headache. Injury to the internal carotid artery may unleash attacks in patients who are predisposed to develop cluster headache. Further study on the subject is needed to resolve this issue.

Bout-associated intrinsic functional network changes in cluster headache: A longitudinal resting-state functional MRI study

Background Previous imaging studies on the pathogenesis of cluster headache (CH) have implicated the hypothalamus and multiple brain networks. However, very little is known regarding dynamic bout-associated, large-scale resting state functional network changes related to CH. Methods Resting-state functional magnetic resonance imaging data were obtained from CH patients and matched controls. Data were analyzed using independent component analysis for exploratory assessment of the changes in intrinsic brain networks and their relationship between in-bout and out-of-bout periods, as well as correlations with clinical observations. Results Compared to healthy controls, CH patients had functional connectivity (FC) changes in the temporal, frontal, salience, default mode, somatosensory, dorsal attention, and visual networks, independent of bout period. Compared to out-of-bout scans, in-bout scans showed altered FC in the frontal and dorsal attention networks. Lower frontal network FC correlated with longer duration of CH. Conclusions The present findings suggest that episodic CH with dynamic bout period shifts may involve bout-associated FC changes in multiple discrete cortical areas within networks outside traditional pain processing areas. Dynamic changes in FC in frontal and dorsal attention networks between bout periods could be important for understanding episodic CH pathophysiology.

Chronic cluster headache and the pituitary gland

BACKGROUND

Cluster headache is classified as a primary headache by definition not caused by an underlying pathology. However, symptomatic cases of otherwise typical cluster headache have been reported.

CASE PRESENTATION

A 47-year-old male suffered from primary chronic cluster headache (CCH, ICHD-3 beta criteria fulfilled) since the age of 35 years. A magnetic resonance imaging (MRI) study of the brain in 2006 came back normal. He tried several prophylactic treatments but was never longer than 1 month without attacks. He was under chronic treatment with verapamil with only a limited effect on the attack frequency. Subcutaneous sumatriptan 6 mg injections were very effective in aborting attacks. By February 2014 the patient developed a continuous interictal pain ipsilateral to the right-sided cluster headache attacks. An indomethacin test (up to 225 mg/day orally) was negative. Because of the change in headache pattern we performed a new brain MRI, which showed a cystic structure in the pituitary gland. The differential diagnosis was between a Rathke cleft cyst and a cystic adenoma. Pituitary function tests showed an elevated serum prolactin level. A dopamine agonist (cabergoline) was started and the headache subsided completely. Potential pathophysiological mechanisms of pituitary tumor-associated headache are discussed.

CONCLUSION

Neuroimaging should be considered in all patients with CCH, especially those with an atypical presentation or evolution. Response to acute treatment does not exclude a secondary form of cluster headache. There may be shared pathophysiological mechanisms of primary and secondary cluster headache.

Neural Plasticity in Common Forms of Chronic Headaches

Headaches are universal experiences and among the most common disorders. While headache may be physiological in the acute setting, it can become a pathological and persistent condition. The mechanisms underlying the transition from episodic to chronic pain have been the subject of intense study. Using physiological and imaging methods, researchers have identified a number of different forms of neural plasticity associated with migraine and other headaches, including peripheral and central sensitization, and alterations in the endogenous mechanisms of pain modulation. While these changes have been proposed to contribute to headache and pain chronification, some findings are likely the results of repetitive noxious stimulation, such as atrophy of brain areas involved in pain perception and modulation. In this review, we provide a narrative overview of recent advances on the neuroimaging, electrophysiological and genetic aspects of neural plasticity associated with the most common forms of chronic headaches, including migraine, cluster headache, tension-type headache, and medication overuse headache.

Altered hypothalamic functional connectivity in cluster headache: a longitudinal resting-state functional MRI study

BACKGROUND

Neuroimaging studies implicate hypothalamic dysfunction in the pathogenesis of cluster headache (CH). Disruptions in non-traditional pain processing areas, including the cerebellum and visual cortex, have also been reported in CH. It is unknown whether the hypothalamus interacts significantly with these areas, and whether any such interactions vary between the 'in-bout' and 'out-of-bout' periods in CH. This study aimed to investigate the resting-state functional connectivity (FC) of the hypothalamus of patients with CH.

METHODS

Using 3-T functional MRI, we conducted a seed-based resting-state intrinsic FC analysis of the hypothalamus in 18 episodic CH patients during in-bout and out-of-bout periods, and in 19 healthy controls. Correlations between hypothalamic FC and clinical variables were also assessed.

RESULTS

Compared to controls, CH patients showed hypothalamic FC changes with the medial frontal gyrus and occipital cuneus during in-bout and out-of-bout periods. Compared to out-of-bout scans, in-bout scans revealed decreased hypothalamic FC with the medial frontal gyrus, precuneus, and cerebellar areas (tonsil, declive and culmen). Additionally, the annual bout frequency correlated significantly with the hypothalamic FC in the cerebellar culmen (r=-0.576, p=0.02) and cerebellar declive (r=-0.522, p=0.038).

CONCLUSIONS

Our findings suggest that in CH, FC differences between the hypothalamus and its regional distribution extends beyond traditional pain processing areas, primarily to the cerebellar, frontal and occipital areas. These changes may be important and associated with CH pathophysiology.

The Neuropharmacology of Cluster Headache and other Trigeminal Autonomic Cephalalgias

Trigeminal autonomic cephalalgias (TACs) are a group of primary headaches including cluster headache (CH), paroxysmal hemicrania (PH) and short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT). Another form, hemicrania continua (HC), is also included this group due to its clinical and pathophysiological similarities. CH is the most common of these syndromes, the others being infrequent in the general population. The pathophysiology of the TACs has been partly elucidated by a number of recent neuroimaging studies, which implicate brain regions associated with nociception (pain matrix). In addition, the hypothalamic activation observed in the course of TAC attacks and the observed efficacy of hypothalamic neurostimulation in CH patients suggest that the hypothalamus is another key structure. Hypothalamic activation may indeed be involved in attack initiation, but it may also lead to a condition of central facilitation underlying the recurrence of pain episodes. The TACs share many pathophysiological features, but are characterised by differences in attack duration and frequency, and to some extent treatment response. Although alternative strategies for the TACs, especially CH, are now emerging (such as neurostimulation techniques), this review focuses on the available pharmacological treatments complying with the most recent guidelines. We discuss the clinical efficacy and tolerability of the currently used drugs. Due to the low frequency of most TACs, few randomised controlled trials have been conducted. The therapies of choice in CH continue to be the triptans and oxygen for acute treatment, and verapamil and lithium for prevention, but promising results have recently been obtained with novel modes of administration of the triptans and other agents, and several other treatments are currently under study. Indomethacin is extremely effective in PH and HC, while antiepileptic drugs (especially lamotrigine) appear to be increasingly useful in SUNCT. We highlight the need for appropriate studies investigating treatments for these rare, but lifelong and disabling conditions.

Structural imaging in cluster headache

Cluster headache is a rare primary headache disorder and the most common trigeminal-autonomic cephalalgia. Even though it has been extensively studied, its pathophysiology remains nebulous. Over the last two decades, cerebral imaging has increasingly been used to aid the investigation of pain and headache disorders. Pioneering work using magnetic resonance-based, voxel-based morphometry depicted an isolated increase of grey matter in the posterior hypothalamus and thereby reconfirmed the most commonly accepted pathophysiological concept. More recent works demonstrate structural changes across multiple structures related to pain processing, sensory integration, and emotional evaluation. These changes do not seem to be static, but rather appear to be dynamic in nature as they change over the course of the disease. This was interpreted as a reflection of the plasticity of the human brain and should guide future thoughts towards a more complex pathophysiological model involving a maladaptive pain modulatory network.

Cortical plasticity in episodic and chronic cluster headache

Cluster headache (CH) is characterized by recurrent episodes of excruciatingly painful, unilateral headache attacks typically accompanied by trigeminal autonomic symptoms. Due to its rhythm with alternating episodes of pain and no-pain, it is an excellent model to investigate whether structural brain changes detected by magnetic resonance based voxel-based-morphometry (VBM) reflect the cause of the disease, may be a consequence of the underlying disease other than pain, or may simply be caused by the sensation of pain itself. We investigated 91 patients with CH in different stages of their disease using VBM and compared them to 78 age- and gender-matched healthy controls. We detected distinct regional gray matter (GM) changes in different brain regions including the temporal lobe, the hippocampus, the insular cortex and the cerebellum. The extent, location and direction of observed GM alterations depended on the state of disease and appeared dynamic in relation to pain state (i.e., pain vs. no-pain). No hypothalamic changes were detected in CH patients compared to healthy controls. The GM changes observed in this study are highly dynamic and thereby reflect the cortical plasticity of the brain in regard to pain. This observed dynamic may provide an explanation of the diverse results of previous VBM studies in pain. Regarding CH the results suggest that the disease is more likely to be caused by a network dysfunction rather than by a single malfunctioning structure.

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We identified gray matter (GM) changes in pain processing areas and beyond in patients suffering cluster headache (CH) compared to healthy controls

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GM changes significantly differed for different courses of the disease (chronic, episodic inside bout, episodic outside bout).

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GM decrease was predominantly observed in chronic CH, while episodic CH showed a more complex and partly opposite behavior.

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This dynamic probably reflects the brain's adaptation capacity to changing stimuli in regard to cortical plasticity and may provide an explanation of the diverse results of previous VBM studies in pain

Cognitive processing of cluster headache patients: evidence from event-related potentials

BACKGROUND

The peripheral and central origins of pain in cluster headache (CH) have been a matter of much debate. The development and application of functional imaging techniques have provided more evidence supporting the hypothesis that CH is not a disorder exclusively peripheral in origin, and in fact central regions might be more important. Event-related potentials confer advantages in the functional evaluation of the cortex, but few studies thus far have employed this method in cluster headache.

METHODS

Seventeen cluster patients (15 males; mean age = 35.4 years) and 15 age-matched healthy participants (13 males; mean age = 34.6 years) were recruited. A visual oddball paradigm was employed to analyze target processing using event-related potentials. We investigated the P3/P3d components in the experiment.

RESULTS

P3/P3d amplitudes were decreased in CH patients (P3, 3.82 μV; P3d, 5.8 μV) compared with controls (P3, 7.28 μV; P3d, 8.95 μV), F(1,30) = 4.919, p < 0.05, η2 = 0.141 for P3 and F(1,30) = 8.514, p < 0.05, η2 = 0.221 for P3d, respectively). Moreover, the amplitudes of P3/P3d were no significantl difference in the side of pain as compared to contralateral one (p > 0.05).

CONCLUSIONS

These results provide evidence of dysfunction in the cognitive processing of CH patients, which may also contribute to the pathophysiology of CH.

Sleep in trigeminal autonomic cephalagias: a review

PURPOSE OF REVIEW

Sleep and cluster headache (CH) are believed to be interconnected but the precise relation to the other trigeminal autonomic cephalalgias (TACs) is uncertain and complex. A better understanding of these relations may eventually lead to a clarification of the underlying mechanisms and eventually to more effective therapeutic regimens. This review aims to evaluate the existing literature on the subject of TACs and sleep. An association between episodic CH and distinct macrostructural sleep phases, especially the relation to rapid eye movement (REM) sleep, has been described in some older studies but could not be confirmed in other, more recent studies. Investigations into the microstructure of sleep in these patients are lacking. Only a few case reports exist on the relation between sleep and other TACs.

SUMMARY

Recent studies do not find an association between CH and REM sleep. One older study suggests chronic paroxysmal hemicranias may be locked to REM sleep but otherwise the relation is unknown. Reports indicate that CH and obstructive sleep apnoea are associated in some individuals but results are diverging. Single cases show improvement of CH upon treatment of sleep apnoea, but the causal relationship remains in question. Other TACs are probably not connected to sleep and strictly nocturnal attacks should prompt investigations for secondary causes. The relation between CH and sleep is, however, fascinating and detailed sleep studies in carefully diagnosed patients are warranted.

Altered white matter microstructural connectivity in cluster headaches: a longitudinal diffusion tensor imaging study

BACKGROUND

Functional and structural disruptions to the pain matrix, which may involve changes in white matter (WM) pathways connecting the pain-processing system and hypothalamus, have been implicated in the pathophysiology of cluster headache (CH). However, previous studies have obtained inconclusive results regarding WM changes in CH, and WM variations between "in-bout" and "out-of-bout" periods of CH remain to be determined.

METHODS

Multiple diffusivity indices obtained by diffusion tensor imaging (DTI) and post-hoc probabilistic tractography were used to elucidate CH pathophysiology.

RESULTS

Compared to healthy participants, in-bout CH patients showed regionally higher absolute (radial and mean) diffusivities in the left medial frontal gyrus and frontal sub-gyrus and lower absolute (axial, radial and mean) diffusivities in the right parahippocampal gyrus of the limbic lobe. These changes during the in-bout period generally persisted in the out-of-bout period, except for the left cerebellar tonsil. Post-hoc probabilistic tractography showed highly consistent anatomical connections between these altered areas and the hypothalamus across participants.

CONCLUSIONS

Distinct WM changes were observed in episodic CH. Connections between the pain-modulation areas and hypothalamus may be involved in CH pathophysiology.