Cluster headache overview

# Overview
Cluster headaches are rare, extremely painful and debilitating headaches that occur in groups or clusters. Often appearing during seasonal changes. They may also be described as suicide headaches, a reference to the excruciating pain and resulting desperation that has culminated in actual suicide. Cluster headaches are classified as vascular headaches. The intense pain is caused by the dilation of blood vessels which creates pressure on the trigeminal nerve. While this process is the immediate cause of the pain, the etiology (underlying cause or causes) is not fully understood. Differential of cluster headache usually involves syndromes that manifest as unilateral headache, brief but frequent attacks. Such syndromes include the following: Chronic paroxysmal hemicrania (CPH) , Short-lasting unilateral neuralgiform headache attacks, Trigeminal neuralgia, primary stabbing headache, and headache associated with an underlying intracranial lesion. Patients with cluster headaches usually have an underlying secondary cause of headaches such as structural brain lesion, TBI and genetic predisposition that may increase the risk of cluster headache.  Cluster headache is one of the most common trigeminal autonomic cephalalgias. It is a life long condition and usually results in reduced quality of life and marked functional disability. Although, the frequency of episodes usually decrease with age, 80% of patients continue to experience the attacks even after 15 years of onset.  Diagnostic criteria for cluster headache require the following as per ICHD-3: International Classification of Headache Disorders, 3rd edition. Cluster headache sufferers typically experience very severe headaches of a piercing quality near one eye or temple that last for fifteen minutes to three hours with some lasting days (rarely more than three days). The headaches are typically unilateral and rarely change sides during the same cycle (see episodic). Cluster headaches have a characteristic circadian periodicity and usually present with autonomic symptoms. Neuro-imaging with an magnetic resonance imaging (MRI) scan with and without contrast  is preferred to non-contrast computed tomography (CT) scan. MRI is usually indicated to rule out underlying structural brain lesion or to evaluate brain and pituitary gland in patient presenting with typical features or highly suspicious of cluster headache. Cluster headache treatment is generally divided into acute therapy or abortive therapy focused at aborting individual attacks and preventive or prophylactic therapy aimed at preventing recurrent attacks during the cluster period. Cluster headaches often go undiagnosed for many years, being confused with migraine or other causes of headache. Because of the relative rareness of the condition and ambiguity of the symptoms, some sufferers may not receive treatment in the emergency room and patients may even be mistaken as exhibiting drug-seeking behavior. Over-the-counter pain medications (such as aspirin, paracetamol, and ibuprofen) typically have no effect on the pain from a cluster headache. Unlike other headaches such as migraines and tension headaches, cluster headaches do not respond to biofeedback. Some have reported partial relief from narcotic pain killers. Percocet (Oxycodone with paracetamol) has had widespread success amongst some cluster headache patients, especially males. Anecdotal evidence indicates that cluster headaches can be so excruciating that even morphine does little to ease the pain. However, some newer medications like fentanyl (and Percocet) have shown promise in early studies and use. The drug of choice for primary prevention of cluster headache is Verapamil. Other agents that can be used also include glucocorticoids, topiramate and lithium.

# Historical Perspective
Cluster headaches have been called by several other names in the past including Erythroprosopalgia of Bing, ciliary neuralgia, migrainous neuralgia, erythromelagia of the head, Horton's headache, histaminic cephalalgia, petrosal neuralgia, sphenopalatine neuralgia, Vidian neuralgia, Sluder's neuralgia, and hemicrania angioparalyticia. In 1952, cluster headache was named by American physician E. Charles Kunkle. In 1998, cluster headache was established as a separate entity by International Classification of Headache Disorders (ICHD-I). In 2004, restlessness/agitation was added with the ICHD-II revision. In 2013, two new autonomic features were added in the ICHD-III-beta revision in 2013.2.

# Pathophysiology
The clear pathogenesis of cluster headache is still unknown. Various thought processes and pathophysiologic mechanism are considered to be involved in the pathogenesis. Generally 3 brain systems are mostly found to be involved or associated with the pathophysiology of cluster headache. Three brain systems are thought to be involved: hypothalamus, autonomic system and trigeminal nucleus. Orexin/hypocretin receptor 2 (HCRTR2) gene mutations are found to be particularly associated with cluster headaches in a couple of separate independent studies. Cluster headaches may also be associated with or secondary to other conditions such as: Hypothalamic and pituitary tumors, meningiomas (anywhere from the cavernous sinus to the upper cervical spine), carotid artery dissections, vascular malformations and sleep apnea.

# Causes
Cluster headaches are generally associated with underlying neurologic conditions and structural abnormalities of brain and the pituitary gland. Common causes include; Chronic paroxysmal hemicrania (CPH), Subarachnoid hemorrhage, Trigeminal Neuralgia, Cyclical migraine, Hemicrania continua, Intermittent hydrocephalus, Sleep apnea, Acute optic neuritis, Acute glaucoma, Acute hypertension, Cerebral venous thrombosis, and Interior carotid artery dissection.

# Differentiating Cluster Headache from other Diseases
Differential of cluster headache usually involves syndromes that manifest as unilateral headache, brief but frequent attacks. Such syndromes include the following: Chronic paroxysmal hemicrania (CPH) , Short-lasting unilateral neuralgiform headache attacks, Trigeminal neuralgia, primary stabbing headache, and headache associated with an underlying intracranial lesion.

# Epidemiology and Demographics
The prevalence of cluster headache is <1 percent and mostly affects men. A meta-analysis of 16 population-based epidemiologic studies showed that the lifetime prevalence of cluster headache for adults of all ages was 0.1 percent and the 1 year prevalence of cluster headache was 53 per 100,000.

# Risk Factors
Patients with cluster headaches usually have an underlying secondary cause of headaches such as structural brain lesion, TBI and genetic predisposition that may increase the risk of cluster headache.

# Natural History, Complications and Prognosis
Cluster headache is one of the most common trigeminal autonomic cephalalgias. It is a life long condition and usually results in reduced quality of life and marked functional disability. Although, the frequency of episodes usually decrease with age, 80% of patients continue to experience the attacks even after 15 years of onset.

# Diagnostic Criteria
Diagnostic criteria for cluster headache require the following as per ICHD-3: International Classification of Headache Disorders, 3rd edition.

# History and Symptoms
Cluster headache sufferers typically experience very severe headaches of a piercing quality near one eye or temple that last for fifteen minutes to three hours with some lasting days (rarely more than three days). The headaches are typically unilateral and rarely change sides during the same cycle (see episodic). Cluster headaches have a characteristic circadian periodicity and usually present with autonomic symptoms.

# Physical Examination
Examination findings in cluster headache are usually autonomic related; suggesting parasympathetic hyperactivity and sympathetic impairment. Exam findings may include ptosis, lacrimation, conjuctival injection, miosis, nasal congestion, rhinorrhea, neck stiffness and photophobia.

# Laboratory Findings
Laboratory investigations, such as electrophysiologic testing (eg, evoked potential, electroencephalography) and examination of the cerebrospinal fluid, are not found to be helpful and needs more studies for further evaluation.

# CT
Neuro-imaging with a non-contrast computed tomography (CT) scan is usually indicated to rule out underlying structural brain lesion or to evaluate brain and pituitary gland in patient presenting with typical features or highly suspicious of cluster headache.

# MRI
Neuro-imaging with an magnetic resonance imaging (MRI) scan with and without contrast  is preferred to non-contrast computed tomography (CT) scan. MRI is usually indicated to rule out underlying structural brain lesion or to evaluate brain and pituitary gland in patient presenting with typical features or highly suspicious of cluster headache.

# Treatment
Cluster headache treatment is generally divided into acute therapy or abortive therapy focused at aborting individual attacks and preventive or prophylactic therapy aimed at preventing recurrent attacks during the cluster period. Cluster headaches often go undiagnosed for many years, being confused with migraine or other causes of headache. Because of the relative rareness of the condition and ambiguity of the symptoms, some sufferers may not receive treatment in the emergency room and patients may even be mistaken as exhibiting drug-seeking behavior. Over-the-counter pain medications (such as aspirin, paracetamol, and ibuprofen) typically have no effect on the pain from a cluster headache. Unlike other headaches such as migraines and tension headaches, cluster headaches do not respond to biofeedback. Some have reported partial relief from narcotic pain killers. Percocet (Oxycodone with paracetamol) has had widespread success amongst some cluster headache patients, especially males. Anecdotal evidence indicates that cluster headaches can be so excruciating that even morphine does little to ease the pain. However, some newer medications like fentanyl (and Percocet) have shown promise in early studies and use.

# Prevention
The drug of choice for primary prevention of cluster headache is Verapamil. Other agents that can be used also include glucocorticoids, topiramate and lithium.