Sex Differences in Clinical Features, Treatment, and Lifestyle Factors in Patients With Cluster Headache

Characteristics of men and women with medically diagnosed cluster headache in a national integrated healthcare system: A Veterans Health Administration cohort study

OBJECTIVE

Describe the epidemiology of cluster headache (CH) using Veterans Health Administration (VHA) Electronic Health Record (EHR) data.

BACKGROUND

Epidemiologic studies of CH at the population level are difficult because it has a prevalence of ~0.1%. Hospital system-wide studies are an attractive alternative as they have large numbers of patients and broader populations than headache or neurology clinic-based studies. The VHA is an ideal hospital-based system in which to study CH because it is nationwide, predominantly male, has a strong focus on mood disorders and suicidality, and has accessible individual medical records. Here, we report the first headache study based on an ongoing longitudinal cohort of patients with CH using VHA EHR data.

METHODS

The VHA EHR data were accessed from Fiscal Year 2008 to 2019. Patients with CH consisted of all patients with at least one outpatient visit containing a CH diagnosis code from the International Classification of Diseases (ICD)-9 or -10. We extracted data on demographic features, incidence, and prevalence, as well as pain and psychiatric comorbidities.

RESULTS

Of the 1,524,960 distinct patients who presented for headache treatment in the VHA between Fiscal Year 2008-2019, 24,131 had at least one visit with a CH diagnosis. The 1-year period prevalence of a CH diagnosis in the VHA ranges from 0.08% to 0.10% for women and 0.10% to 0.18% for men. A larger proportion of women versus men received a diagnosis of unspecified CH (59.6% [1412/2368] vs. 53.6% [11,663/21,763], p < 0.001). Most patients with CH had both comorbid headache and non-headache pain diagnoses. Headache not-otherwise-specified was the most common comorbid headache disorder at 70.0% (16,885/24,131) and was more common in women (76.1%, 1801/2368) compared to men (69.3%, 15,084/21,763). Other common comorbidities included migraine, depression, tobacco use, and obstructive sleep apnea. Rates of suicidal ideation or attempt were almost 50% higher in women (5-year proportion 9.4%, 222/2368) with CH compared to men (6.6%, 1433/21,763).

CONCLUSIONS

To our knowledge this is the largest hospital system study of CH to date and reinforces several previous studies. Pain, mental health, and sleep disorders comorbidities are particularly prevalent in this group and were often more common in women compared to men with CH. Future work should examine gender and race stratified prevalence estimates within the VHA and other healthcare systems.

Sex differences in the clinical manifestations and treatment outcomes in a large cohort of spontaneous intracranial hypotension

OBJECTIVE

To determine sex differences in clinical profiles and treatment outcomes in patients with spontaneous intracranial hypotension.

BACKGROUND

Spontaneous intracranial hypotension is associated with considerable functional disability and potentially fatal complications, and it is uncertain whether males and females should be managed differently.

METHODS

This was a cohort study of consecutive patients with spontaneous intracranial hypotension enrolled from a medical center. Medical records and imaging findings were reviewed. The outcome of treatment responses to epidural blood patches and risks of subdural hematoma were measured.

RESULTS

In total, 442 patients with spontaneous intracranial hypotension (165 males, 277 females) were included in the analysis. Males were more likely to have a delayed (>30 days) initial presentation than females (32.1% [53/165] vs. 19.9% [55/277], p = 0.004), and males were less likely to have nausea (55.8% [92/165] vs. 67.1% [186/277], p = 0.016), vomiting (43.0% [71/165] vs. 54.2% [150/277], p = 0.024), photophobia (9.7% [16/165] vs. 17.0% [47/277], p = 0.034), and tinnitus (26.7% [44/165] vs. 39.7% [110/277], p = 0.005) compared with females despite comparable radiologic findings. Among the 374 patients treated with epidural blood patches, males were more likely to be nonresponders to the first epidural blood patch (58.0% [80/138] vs. 39.0% [92/236], OR = 2.2, 95% CI = 1.4-3.3, p < 0.001). Males were at a higher risk of having subdural hematoma (29.7% [49/165] vs. 10.8% [30/277], OR = 3.5, 95% CI = 2.1-5.8, p < 0.001). Among patients with subdural hematoma, males had greater thickness (12.8 ± 4.3 vs. 8.1 ± 5.9 mm, p < 0.001) and were more likely to receive surgical drainage (55.1% [27/49] vs. 10.0% [3/30], OR = 11.0, 95% CI = 3.0-41.3, p < 0.001) than females.

CONCLUSION

In the present study, spontaneous intracranial hypotension in males was characterized by a delayed presentation, poorer response to the first epidural blood patch, and a higher risk of subdural hematoma. Caution should be exercised in the management of males with spontaneous intracranial hypotension. The generalizability of the findings needs to be further confirmed.

Recent advances in diagnosing, managing, and understanding the pathophysiology of cluster headache

Cluster headache, characterised by attacks of severe, recurrent, unilateral headache and ipsilateral cranial autonomic symptoms, remains a primary headache with an elusive pathophysiology. Recent advances have introduced effective treatments and broadened understanding of the clinical features of cluster headache. These features are similar in patients globally, but regional differences in prevalence and burden exist. International collaborations have led to identification of eight genetic loci associated with cluster headache. The pathophysiological mechanisms are still not fully understood but recent studies show that targeting the trigeminal autonomic reflex by neurostimulation, or targeting the neuropeptide calcitonin gene-related peptide (CGRP), might lessen the attack burden. The US Food and Drug Administration has approved galcanezumab, a monoclonal antibody targeting CGRP, as the first specific preventive treatment for episodic cluster headache. However, a preventive effect was not replicated in chronic cluster headache, and the European Medicines Agency did not approve galcanezumab, restricting its availability in Europe. Owing to the low prevalence of cluster headache, continued collaboration through multicentre clinical trials and data sharing will be imperative for further breakthroughs in understanding and management.

The Prevalence and Clinical Phenotypes of Cluster Headache in Relation with Latitude

PURPOSE OF REVIEW

Previous studies have indicated a possible link between the prevalence of cluster headache (CH) and sunlight exposure. However, this theory has yet to be tested systemically. In this article, we aim to examine how latitude affects the prevalence and phenotypes of CH.

RECENT FINDINGS

To our knowledge, there is by far no article describing the effect of latitude on disease phenotype; thus, we performed a literature review. We noted positive effects of latitude on 1-year prevalence, the proportion of chronic CH, and the proportion of miosis and/or ptosis. Latitude may affect the phenotypic presentations of cluster headache, probably partially mediated via temperature and sunlight variations. Still, other factors, such as environmental exposure to smoking and the genetic difference between the Eastern and Western populations, may participate in the pathogenesis and clinical manifestations of CH.

Clinical predictors of therapeutic failure of occipital nerve stimulation in refractory chronic cluster headache

BACKGROUND

Occipital nerve stimulation (ONS) is a treatment with evidence in refractory chronic cluster headache (CCH). However, the variable response rate and cost make it necessary to investigate predictors of response.

METHODS

This is a cross-sectional study conducted through the review of medical records of CCH patients from six hospitals in Madrid. Epidemiological and clinical variables were compared between patients with ONS failure and the rest. ONS failure was defined as the need for device withdrawal or switch off because of lack of response or adverse events.

RESULTS

From a series of 88 CCH, 26 (29.6%) underwent ONS surgery, of whom 13/26 (50.0%) failed because lack of response. ONS failure group had an earlier headache onset (mean ± SD) of 27.7 ± 6.9 vs. 36.7 ± 11.8 years, p = 0.026) and a higher smoking rate (100% vs. 42.9%, p = 0.006). Stational fluctuations (58.3% vs. 7.7%, p = 0.007) and nocturnal exacerbations (91.7% vs. 53.9%, p = 0.035) were more frequent in the ONS failure group as well. There was no difference between groups in diagnostic delay, years of evolution prior to surgery, mental illness, comorbidity with other headache disorders or chronic pain conditions or prior response to occipital nerves anesthetic blocks.

CONCLUSIONS

Some clinical features such as an early debut, smoking and seasonal or circadian fluctuations could be related to failure of ONS in refractory CCH.

Genetic and Phenotypic Profiling of Triptan Users in a Swedish Cluster Headache Cohort

Up to 25% of individuals who live with cluster headache (CH), an extremely painful primary headache disorder, do not adequately respond to the first-line treatment, triptans. Studies have indicated that genetic variants can play a role in treatment response. Likewise, differences in clinical characteristics can give clues to mechanisms underlying triptan non-response. Our aim was to investigate five genetic variants previously implicated in triptan response and their relation to triptan usage in our Swedish CH cohort and to investigate potential distinctions in clinical characteristics. 545 CH patients were screened for the genetic variants rs1024905, rs6724624, rs4795541, rs5443, and rs2651899 with a case control design based on triptan usage. Analysis of clinical characteristics was based on self-reported questionnaire data from 893 patients. One genetic variant, rs1024905, was significantly associated with triptan non-usage in CH (Pc = 0.010). In addition, multi-allele effector analysis showed that individuals with a higher number of effector variants were less likely to use triptans (P = 0.007). Analysis of clinical characteristics showed that triptan users were more likely to have alcohol as a trigger (57.4% vs 43.4%, P = 0.002), have autonomic symptoms (95.1% vs 88.1%, P = 0.002), and be current smokers (27.0% vs 21.9%, P = 0.033) compared to non-users. These results support the hypothesis that genetic variants can play a role in triptan usage in CH and that patients with a typical CH phenotype are more likely to use triptans.

Cluster Headache, SUNCT, and SUNA

OBJECTIVE

This article reviews the epidemiology, clinical features, differential diagnosis, pathophysiology, and management of three types of trigeminal autonomic cephalalgias: cluster headache (the most common), short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA).

LATEST DEVELOPMENTS

The first-line treatments for trigeminal autonomic cephalalgias have not changed in recent years: cluster headache is managed with oxygen, triptans, and verapamil, and SUNCT and SUNA are managed with lamotrigine. However, new successful clinical trials of high-dose prednisone, high-dose galcanezumab, and occipital nerve stimulation provide additional options for patients with cluster headache. Furthermore, new genetic and imaging tests in patients with cluster headache hold promise for a better understanding of its pathophysiology.

ESSENTIAL POINTS

The trigeminal autonomic cephalalgias are a group of diseases that appear similar to each other and other headache disorders but have important differences. Proper diagnosis is crucial for proper treatment.

Cluster headache: an update on clinical features, epidemiology, pathophysiology, diagnosis, and treatment

Cluster headache (CH) is one of the worst primary headaches that remain underdiagnosed and inappropriately treated. There are recent advances in the understanding of this disease and available treatments. This paper aims to review CH's recent clinical and pathophysiological findings, diagnosis, and treatment. We performed a narrative literature review on the socio-demographics, clinical presentations, pathophysiological findings, and diagnosis and treatment of CH. CH affects 0.1% of the population with an incidence of 2.07-9.8/100,00 person-years-habitants, a mean prevalence of 53/100,000 inhabitants (3-150/100,000 inhabitants). The male-to-female ratio remains inconclusive, as the ratio of 4.3:1 has recently been modified to 1.3-2.6, possibly due to previous misdiagnosis in women. Episodic presentation is the most frequent (80%). It is a polygenetic and multifactorial entity that involves dysfunction of the trigeminovascular system, the trigeminal autonomic reflex, and the hypothalamic networks. An MRI of the brain is mandatory to exclude secondary etiologies. There are effective and safe pharmacological treatments oxygen, sphenopalatine, and great occipital nerve block, with the heterogeneity of clinical trial designs for patients with CH divided into acute, transitional, or bridge treatment (prednisone) and preventive interventions. In conclusion, CH remains underdiagnosed, mainly due to a lack of awareness within the medical community, frequently causing a long delay in reaching a final diagnosis. Recent advances in understanding the principal risk factors and underlying pathophysiology exist. There are new therapeutic possibilities that are effective for CH. Indeed, a better understanding of this challenging pathology will continue to be a subject of research, study, and discoveries in its diagnostic and therapeutic approach.

Profile of Chinese Cluster Headache Register Individual Study (CHRIS): Clinical characteristics, diagnosis and treatment status data of 816 patients in China

BACKGROUND

The clinical profile of cluster headache may differ among different regions of the world, warranting interest in the data obtained from the initial Chinese Cluster Headache Register Individual Study (CHRIS) for better understanding.

METHODS

We conducted a multicenter, prospective, longitudinal cohort study on cluster headache across all 31 provinces of China, aiming to gather clinical characteristics, treatment approaches, imaging, electrophysiological and biological samples.

RESULTS

In total 816 patients were enrolled with a male-to-female ratio of 4.33:1. The mean age at consultation was 34.98 ± 9.91 years, and 24.89 ± 9.77 years at onset. Only 2.33% were diagnosed with chronic cluster headache, and 6.99% had a family history of the condition. The most common bout was one to two times per year (45.96%), lasting two weeks to one month (44.00%), and occurring frequently in spring (76.23%) and winter (73.04%). Of these, 68.50% experienced one to two attacks per day, with the majority lasting one to two hours (45.59%). The most common time for attacks was between 9 am and 12 pm (75.86%), followed by 1 am and 3 am (43.48%). Lacrimation (78.80%) was the most predominant autonomic symptom reported. Furthermore, 39.22% of patients experienced a delay of 10 years or more in receiving a correct diagnosis. Only 35.67% and 24.26% of patients received common acute and preventive treatments, respectively.

CONCLUSION

Due to differences in ethnicity, genetics and lifestyle conditions, CHRIS has provided valuable baseline data from China. By establishing a dynamic cohort with comprehensive multidimensional data, it aims to advance the management system for cluster headache in China.

Clinical characteristics and treatment patterns of patients with episodic cluster headache: results from the United States, United Kingdom and Germany

OBJECTIVE

To describe clinical characteristics and regional treatment patterns of episodic cluster headache (CH).

METHODS

A point-in-time survey of physicians and their patients with CH was conducted in the United States, United Kingdom and Germany in 2017.

RESULTS

Overall, 1012 patients with episodic CH were analyzed. Demographic and clinical findings were generally consistent across regions. Most patients were men (66.6%) and the mean age was 40.9 years. The greatest proportion of patients (38.3%) had ≤1 attack per day. The mean number of attacks per day (APD) was 2.4 and mean number of cluster periods per year was 2.6; the mean cluster period duration was 30.8 days. Most patients (69.3%) did not report a specific or predicable time when cluster periods occurred. Acute treatment was prescribed for 47.6% of patients, 10.3% of patients received preventive treatment, and 37.9% of patients received combined acute and preventive treatment; 4.2% of patients were not receiving treatment. Frequently prescribed acute treatments were sumatriptan, oxygen, and zolmitriptan; oxygen use varied considerably across countries and was prescribed least often in the United States. Frequently prescribed preventive treatments were verapamil, topiramate, and lithium. Lack of efficacy and tolerability were the most common reasons for discontinuing preventive treatment.

CONCLUSIONS

We observed high use of acute treatments, but only half of patients used preventive treatments despite experiencing several cluster periods per year with multiple cluster APD. Further studies about the need for and benefits of preventive treatment for episodic CH are warranted.

New management strategies for primary headache disorders: Insights from P4 medicine

Primary headache disorder is the main cause of headache attacks, leading to significant disability and impaired quality of life. This disorder is increasingly recognized as a heterogeneous condition with a complex network of genetic, environmental, and lifestyle factors. However, the timely diagnosis and effective treatment of these headaches remain challenging. Precision medicine is a potential strategy based on P4 (predictive, preventive, personalized, and participatory) medicine that may bring new insights for headache care. Recent machine learning advances and widely available molecular biology and imaging data have increased the usefulness of this medical strategy. Precision medicine emphasizes classifying headaches according to their risk factors, clinical presentation, and therapy responsiveness to provide individualized headache management. Furthermore, early preventive strategies, mainly utilizing predictive tools, are critical in reducing headache attacks and improving the quality of life of individuals with headaches. The current review comprehensively discusses the potential application value of P4 medicine in headache management.

The genetics and chronobiology of cluster headache

BACKGROUND/HYPOTHESIS

Cluster headache displays uniquely rhythmic patterns in its attack manifestation. This strong chronobiological influence suggests that part of the pathophysiology of cluster headache is distinctly different from migraine and has prompted genetic investigations probing these systems.

METHODS

This is a narrative overview of the cluster headache chronobiological phenotype from the point of view of genetics covering existing knowledge, highlighting the specific challenges in cluster headache and suggesting novel research approaches to overcome these.

RESULTS

The chronobiological features of cluster headache are a hallmark of the disorder and while discrepancies between study results do exist, the main findings are highly reproducible across populations and time. Particular findings in subgroups indicate that the heritability of the disorder is linked to chronobiological systems. Meanwhile, genetic markers of circadian rhythm genes have been implicated in cluster headache, but with conflicting results. However, in two recently published genome wide association studies two of the identified four loci include genes with an involvement in circadian rhythm, MER proto-oncogene, tyrosine kinase and four and a half LIM domains 5. These findings strengthen the involvement of circadian rhythm in cluster headache pathophysiology.

CONCLUSION/INTERPRETATION

Studying chronobiology and genetics in cluster headache presents challenges unique to the disorder. Researchers are overcoming these challenges by pooling various data from different cohorts and performing meta-analyses providing novel insights into a classically enigmatic disorder. Further progress can likely be made by combining deep pheno- and genotyping.

Sex Differences in Neurological Emergencies Presenting to Multiple Urban Level 1 Trauma Centers

Previous studies have suggested that there are sex differences in the treatment and outcome of neurological emergencies; however, research identifying the role these sex differences play in the management of neurological emergencies is lacking. More knowledge of the way sex factors into the pathophysiology of neurological emergencies will be helpful in improving outcomes for these patients. The aim of this cross-sectional study was to assess the prevalence and management of neurological emergencies while evaluating sex differences in the diagnosis and treatment of these emergencies. We analyzed a cohort of 530 adult patients from four level 1 trauma centers over a period of 4 weeks who had a chief complaint of a neurological emergency, including seizures, cerebrovascular events, headache disorders, traumatic brain injuries, and central nervous system infections. Among patients with neurological emergencies, a significantly lower proportion of female patients underwent neurosurgery and were admitted to the intensive care unit compared to male patients, but there were no significant differences between sexes in the time of symptom onset, type of hospital transportation, amount of neuroimaging performed, admission rates, hospital length of stay, and disposition from the emergency department. Although female patients were more likely to have a chief complaint of headache compared to traumatic injuries in male patients, this was not statistically significant. A significantly higher proportion of female patients had health insurance coverage than male patients.

Current treatment options for cluster headache: limitations and the unmet need for better and specific treatments-a consensus article

AIM

Treatment for cluster headache is currently based on a trial-and-error approach. The available preventive treatment is unspecific and based on few and small studies not adhering to modern standards. Therefore, the authors collaborated to discuss acute and preventive treatment in cluster headache, addressing the unmet need of safe and tolerable preventive medication from the perspectives of people with cluster headache and society, headache specialist and cardiologist.

FINDINGS

The impact of cluster headache on personal life is substantial. Mean annual direct and indirect costs of cluster headache are more than 11,000 Euros per patient. For acute treatment, the main problems are treatment response, availability, costs and, for triptans, contraindications and the maximum use allowed. Intermediate treatment with steroids and greater occipital nerve blocks are effective but cannot be used continuously. Preventive treatment is sparsely studied and overall limited by relatively low efficacy and side effects. Neurostimulation is a relevant option for treatment-refractory chronic patients. From a cardiologist's perspective use of verapamil and triptans may be worrisome and regular follow-up is essential when using verapamil and lithium.

CONCLUSION

We find that there is a great and unmet need to pursue novel and targeted preventive modalities to suppress the horrific pain attacks for people with cluster headache.

Epidemiology, burden and clinical spectrum of cluster headache: a global update

BACKGROUND

This narrative review aims to broaden our understanding of the epidemiology, burden and clinical spectrum of cluster headache based on updated findings with a global perspective.

METHODS

We conducted a literature search on the following topics: (a) epidemiology; (b) burden: quality of life, disability, economic burden, job-related burden and suicidality; and (c) clinical spectrum: male predominance and its changes, age, pre-cluster and pre-attack symptoms, aura, post-drome, attack characteristics (location, severity, duration and associated symptoms), bout characteristics (attack frequency, bout duration and bout frequency), circadian and seasonal rhythmicity and disease course.

RESULTS

New large-scale population-based reports have suggested a lower prevalence than previous estimations. The impact of cluster headache creates a significant burden in terms of the quality of life, disability, economic and job-related burdens and suicidality. Several studies have reported decreasing male-to-female ratios and a wide age range at disease onset. The non-headache phases of cluster headache, including pre-cluster, pre-attack and postictal symptoms, have recently been revisited. The latest data regarding attack characteristics, bout characteristics, and circadian and seasonal rhythmicity from different countries have shown variability among bouts, attacks, individuals and ethnicities. Studies on the disease course of cluster headache have shown typical characteristics of attacks or bouts that decrease with time.

CONCLUSIONS

Cluster headache may be more than a "trigeminal autonomic headache" because it involves complex central nervous system phenomena. The spectrum of attacks and bouts is wider than previously recognised. Cluster headache is a dynamic disorder that evolves or regresses over time.

Patients with cluster headache show signs of insomnia and sleep related stress: results from an actigraphy and self-assessed sleep study

BACKGROUND

Cluster headache (CH) is a primary headache disorder which is characterized by circadian timing of headache attacks, usually at nighttime, in around two thirds of patients. Patients with CH often report sleep difficulties, though it is unknown whether this is a cause or a consequence of nightly headache attacks.

OBJECTIVE

In this case-control study we have assessed sleep quality in study participants with CH in cluster bout respectively in remission, compared to a control group of neurologically healthy individuals to investigate the potential connection between sleep and CH.

METHODS

Fifty study participants with CH and 42 controls were recruited for sleep assessment. Sleep was recorded using MotionWatch 8 actigraphs (CamNTech) for a period of two weeks. Study participants were instructed to wear the unit during rest and sleep and to fill out a sleep diary daily through the two-weeks period.

RESULTS

Results from actigraphy recordings and sleep diaries suggested that patients with CH spend longer time in bed than controls (CH 8.1 hours vs. Controls 7.7 hours, p=0.03), but do not sleep more than controls (CH 6.7 hours vs. controls 6.5 hours, p=0.3). In addition, CH patients reported increased sleep latency (p=0.003), particularly during, but not restricted to, cluster bouts. Study participants with CH further reported higher levels of stress at bedtime (p=0.01), and they felt less well rested than controls (p=0.001).

CONCLUSION

Our analysis suggests that sleep is negatively affected in CH both in cluster bout and in remission, manifesting in symptoms consistent with insomnia such as prolonged sleep latency and increased time in bed.

Investigating Vitamin D Receptor Genetic Markers in a Cluster Headache Meta-Analysis

Patients diagnosed with the primary headache disorder known as cluster headache (CH) commonly report that their headache attacks occur in patterns of both circadian and seasonal rhythmicity. Vitamin D is essential for a variety of bodily functions and vitamin D levels are largely regulated by daylight exposure in connection with seasonal variation. For this Sweden-based study, the association between CH and three single-nucleotide polymorphisms in the vitamin D receptor gene, rs2228570, rs1544410, and rs731236, were investigated, as well as CH bouts and trigger factors in relation to seasonal and weather changes. Over 600 study participants with CH and 600 controls were genotyped for rs2228570, and genotyping results for rs1544410 and rs731236 were obtained from a previous genome-wide association study. The genotyping results were combined in a meta-analysis, with data from a Greek study. No significant association was found between rs2228570 and CH or the CH subtype in Sweden, nor did the meta-analysis show significant results for any of the three markers. The most common period of the year to experience CH bouts in Sweden was autumn, and conditions linked to weather or weather changes were also identified as potential triggers for CH bouts for a quarter of the responders who reported bout triggers. Though we cannot rule out vitamin D involvement in CH, this study does not indicate any connection between CH and the three vitamin D receptor gene markers.

Sleep and Chronobiology as a Key to Understand Cluster Headache

The cluster headache is a primary headache characterized by attacks of unilateral pain associated with ipsilateral cranial autonomic features. These attacks recur in clusters during the years alternating with periods of complete remission, and their onset is often during the night. This annual and nocturnal periodicity hides a strong and mysterious link among CH, sleep, chronobiology and circadian rhythm. Behind this relationship, there may be the influence of genetic components or of anatomical structures such as the hypothalamus, which are both involved in regulating the biological clock and contributing even to the periodicity of cluster headaches. The bidirectional relationship manifests itself also with the presence of sleep disturbances in patients affected by cluster headaches. What if the key to studying the physiopathology of such disease could rely on the mechanisms of chronobiology? The purpose of this review is to analyze this link in order to interpret the pathophysiology of cluster headaches and the possible therapeutic implications.