Cluster Headaches: A Rare, Yet Debilitating Pain Syndrome
What are Cluster Headaches?
Often referred to as the "alarm clock headache" for its ability to wake people up with severe pain in or around the eye, a cluster headache is one of the most painful and rare forms of headache. Although this pain syndrome only affects 0.1 to 0.3% of the population, those afflicted experience excruciating pain during a cluster attack. Such headaches usually occur quickly and by surprise, and they typically recur over the course of several weeks (Mayo Clinic staff).
People with cluster headaches may experience two types of headache patterns: episodic and chronic. Episodic headaches, the most common form, are also referred to as "cluster periods," or periods during which frequent headaches last for weeks or even months (Lubin). Such attacks are followed by "remission periods," during which the headaches cease with no recurrence for months or even years. Chronic cluster headaches are more infrequent and include symptoms similar to episodic cluster headaches. However, if left untreated, people do not experience sustained remission periods (Sargeant). Fortunately, cluster headaches are neither common nor life-threatening, and present treatments can limit the frequency and alleviate the severity of the headaches.
Symptoms and Risk Factors
Symptoms of cluster headaches include both internal pain and external manifestations. Those afflicted experience severe pain in or around the eye, as well as pain in the surrounding areas of the face, head, neck, and shoulders. Furthermore, sufferers may experience redness, swelling, and tearing of the affected eye, in addition to eyelid drooping, reduced pupil size, and either nasal congestion or runny nose, known as rhinorrhea, on the affected side of the face. Some have described the pain as sharp, burning, or penetrating, while others have classified it as a feeling of the eye being pushed out of its socket (Lubin).
Some populations are at a higher risk for developing cluster headaches than others. Men, smokers, alcohol abusers are more prone to cluster headaches. People with a family history, sleep disorders, and past traumatic head injuries are also at a high risk to have cluster headaches (A.D.A.M., Inc.).
Characteristics of Cluster periods
National Institutes of Health
The cluster periods characteristic of cluster headaches can last from 6 to 12 weeks and may occur seasonally. During a cluster period, people can experience headaches with different frequencies, ranging from once a day to several times a day, though most headaches normally occur a few hours after one goes to sleep at night, compromising sleep quality. A typical cluster headache can last anywhere from 15 minutes to up to 2 hours (Mayo Clinic staff).
A cluster headache typically ends without notice, and the intensity of the headache decreases significantly until it is completely gone. Although people do not feel pain from the headache after it is gone, they are left with feelings of fatigue. Episodic cluster periods are followed by "remission periods," during which people do not experience pain. These periods can last from 6 to 12 months before the afflicted person lapses back into the cluster headache pattern. Depending on the severity, some chronic cluster headaches may last over a year, and remission periods may last for only a month (Mayo Clinic Staff).
The Science Behind Cluster Headaches
Although the pathophysiology of cluster headaches is still unclear, current research has begun to provide insight into several possible sources of origin. Functional imaging studies have shown that the posterior hypothalamus, shown in Figure 1, is active during bouts of cluster headaches, indicating that hypothalamus dysfunction may be the root cause of cluster headaches. Since the hypothalamus controls the circadian rhythm and 50% of cluster headaches occur during the night, these headaches are thought to be associated with the circadian rhythm (Goadsby).
Other studies have implicated activation of the trigeminal nerve, shown in Figure 2, a sensory nerve allowing sensations in the face, in cluster headaches. When the trigeminal nerve is activated, trigeminal neurons release the neurotransmitter Substance P, which is associated with pain syndromes, including cluster headaches. In fact, treatment with the inhibitory hormone somatostatin allowed inhibition of Substance P, which reduced the intensity of pain and duration of the cluster headaches (Caleri et al). Other suggestions behind the cause or propagation of cluster headaches include histamine as a trigger, as well as vascular dilation after the onset of headache pain, and increased levels of mast cells. Continued research on the subject is needed in order to elucidate a more concrete pathway of the pathophysiology of cluster headaches (Sargeant).
Although there is currently no cure for cluster headaches, there are two types of treatments available: prophylactic treatments to prevent onset of headaches and symptomatic therapies for pain management. The prophylactic treatments include induction (acute) and maintenance (long-term) therapies. Induction treatments (including cortocisteroid) break the cluster headache cycle, while maintenance treatments (including calcium channel blockers, such as Verapamil) allow long-term prevention of headaches (health-cares.net). Symptomatic therapies include oxygen inhalation, injection of octreotide (a synthetic version of somatostatin), and intranasal use of local anesthetics, such as lidocaine (health-cares.net, Matharu et al).
Deep Brain Stimulation: Surgical Option
People with drug-resistant chronic cluster headaches are at times recommended to undergo deep brain stimulation. In such rare cases when this surgery is needed, nine electrodes are surgically implanted into the hypothalamus, as seen in Figure 3, and an extension cable connects the neurostimulator to the electrodes. The stimulator produces electrical deep brain stimulation (DBS) of the inferior posterior hypothalamic grey matter, which has been shown to help cluster headaches (Franzini et al).
This treatment is generally safe, but patients require monitoring to prevent complications such as bleeding, infection, and problems with placement of the wire. This method has been widely effective, with 60% of chronic cluster headache patients becoming virtually pain-free after undergoing surgery (Leone et al).
Findings from studies continue to elucidate the pathophysiology behind cluster headaches, allowing development of effective medications and surgical treatments for this pain syndrome and improving the quality of life of those afflicted.