title: Insomnia and periodicity of headache in an arctic cluster headache population.
abstract: OBJECTIVE
  To assess the prevalence of chronic insomnia and the periodicity of headache attacks in an Arctic cluster headache population.
  
  
  BACKGROUND
  Cluster headache is a sleep-related disorder, and attacks have both circadian and circannual rhythmicity.
  
  
  METHODS
  Through a retrospective hospital chart review, we identified all subjects diagnosed with episodic cluster headache (ICD-10 G 44.0) at the Neurological Departments in Northern Norway (located north of 66°33'N) between January 1, 2000 and December 31, 2010. Patients with a confirmed diagnosis (ICHD-2) received a comprehensive questionnaire covering demographic data, clinical characteristics, sleep, and periodicity of attacks.
  
  
  RESULTS
  A total of 196 subjects were registered, and 178 received the questionnaire. The response rate was 88/178 (49%). Fifty-eight men (aged 49.2 ± 13.6) and 12 women (aged 49.7 ± 15.5) were included. Forty percent of the responders suffered from chronic insomnia (Diagnostic and Statistical Manual of Mental Disorders 4th edition). Forty-nine percent of the responders and 42% of the non-responders were shift workers, which is much higher than compared with the general population (24%). Insomnia was significantly associated with shift work and experiencing longer-lasting cluster bouts. One third attributed their insomnia to the cluster headache. Thirty-seven percent reported a seasonal predilection of the cluster periods, and 58% a diurnal periodicity of attacks. Eighty percent often or always had headache attacks during sleep, the most frequent time interval being at 12:00-4:00 am. Shift workers were significantly more likely to see lack of sleep as a cluster attack trigger than daytime workers.
  
  
  CONCLUSIONS
  Chronic insomnia and shift work seem to be common among Arctic cluster headache patients. The small number of subjects included in this study implies that conclusions should be drawn with caution, but the findings support the idea of cluster headache as a circadian rhythm disorder.
authors.affiliation: Nordland Hospital Trust, Bodø, Norway.
authors.forename: Hilde K
authors.initials: HK
authors.lastname: Ofte
authors.forename: Diana H
authors.initials: DH
authors.lastname: Berg
authors.forename: Svein I
authors.initials: SI
authors.lastname: Bekkelund
authors.forename: Karl B
authors.initials: KB
authors.lastname: Alstadhaug
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm / Q000502:physiology*; D003027:Cluster Headache / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010507:Periodicity; D011159:Population Surveillance / Q000379:methods*; D012189:Retrospective Studies; D020178:Sleep Disorders, Circadian Rhythm / Q000175:diagnosis / Q000453:epidemiology*; D007319:Sleep Initiation and Maintenance Disorders / Q000175:diagnosis / Q000453:epidemiology*
keywords: cluster headache; epidemiology; insomnia; periodicity; shift work