Actigraphy and Nocturnal Heartrate Variability in Cluster Headache Patients

Cluster headache (CH) is a primary headache in which recurring episodes of unilateral, periorbital pain is accompanied by unilateral autonomic symptoms such as tearing, conjunctival injection, nasal congestion or rhinorrhea, miosis and ptosis. Headache attacks last from 15 to 180 minutes, and patients may have up to eight attacks each day. Most attacks occur at night between midnight and 04 a.m. Headache attacks come in recurring bouts lasting up to three months, after which the headache disappears for at least one month. 10-15% of patients have chronic cluster headache, meaning that there are no pauses between bouts. The condition has a prevalence of about 0.2% and affects men 3-4 times more often than women.

The combination of unilateral headache and autonomic symptoms makes CH an interesting disorder to study in view of headache pathophysiology. Increasing amounts of evidence points at the hypothalamus as the locus in quo for CH pathophysiology. During attacks, the autonomic symptoms seem to be caused both by a hypofunction of sympathetic activity (miosis and ptosis), and a hyperfunction of parasympathetic activity (conjunctival injection, tearing and nasal congestion). Physiological studies seem to imply that patients during bouts have an upregulated parasympathetic activity caused by activation of the trigemino-parasympathetic reflex and a downregulated sympathetic tone, while they outside of bouts have a downregulated parasympathetic tone. Studying the autonomous nervous system in cluster headache patients is difficult, as they usually have headaches only a few months during the year and the attacks are quite short lasting, but excruciating painful when they occur, leaving the patients restless and with an urge to move about. This makes it difficult to study what actually happens during the painful phase. Thus, finding new ways to study the autonomic nervous system in these patients during the various stages of their disease is very important.

In addition to autonomic dysfunction, sleep disturbances are frequent and well documented in CH patients. Sleep is often problematic in all headaches, but CH patients seem to have a high prevalence of insomnia even when compared to other headache populations. This is not merely a result of the recurring nocturnal headaches, as CH patients have significantly reduced sleep quality compared to controls even one year after last headache attack. The documentation mostly consist of studies using well validated questionnaires such as the Pittsburgh Sleep Quality Index (PSQI) or diagnostic criteria such as the DSM IV. Only one major study have assessed sleep quality in cluster headache using quantitative methods such as polysomnography. In this study, the authors found that cluster headache patients in headache bout had a reduced percentage of REM sleep, longer REM latency and fewer arousals compared to healthy controls. There was no temporal relationship between headache attacks and specific sleep stages. Sleep is the single most important trigger for attacks in cluster headache, and most attacks occur during the late night or early morning hours.

We know that the balance between sympathetic and parasympathetic tone differ between REM and NREM-sleep stages in healthy individuals, and that there is a transient decrease in sympathetic tone during the night, which is reflected in a period of reduced heart rate and blood pressure. This "dipping" coincides with the increased occurrence of cluster attacks, and fits well into the emerging theory that cluster headache attacks is elicited in a state of hypoarousability, or reduced sympathetic tone. Thus, sleep disturbances are, together with autonomic dysfunction, an integral part of CH pathophysiology, and further studies are needed to elucidate the association between sleep, autonomic dysfunction and headache attacks.

The aim of this study is to assess sleep quality and autonomic tone in CH patients inside and outside of headache bouts, compared to healthy controls. Inside of bouts, the investigators will assess how the occurrence of headache attacks are related to autonomic tone. The data will be gathered by using actigraphy, pupillometry and heart-rate variability, all well validated research tools. In addition, all participators will fill out the PSQI reporting subjective sleep quality.