title: Seasonal Variation in Spontaneous Cervical Artery Dissection: Comparing between UK and Australian Sites.
abstract: BACKGROUND
  Cervical artery dissection (CAD) is a leading cause of stroke among middle-aged adults, but the etiology is unclear. Some reports of seasonal variation in CAD incidence have been suggested but may reflect extreme climatic conditions. Seasonal variation may implicate more transient seasonal causes such as proinflammatory or hypercoagulable states. This study aimed to assess whether CAD incidence varied with season between UK and Australian sites. Also, this study aimed to determine whether there was a different pattern of seasonal variation between arteries (carotid and vertebral) and any association between CAD incidence and clinical factors.
  
  
  METHODS
  This was a retrospective observational study of patients older than 18 years with radiological diagnosis of internal carotid or vertebral arterial dissection, from sites in Australia and the UK. Clinical variables were compared between autumn-winter and spring-summer and site of dissection.
  
  
  RESULTS
  A total of 133 CAD cases were documented in Australia and 242 in the UK. There was a seasonal pattern to CAD incidence in countries in both the northern and the southern hemispheres, with a trend for dissection to occur more commonly in autumn, winter, and spring than in summer (incidence rate ratios [IRR] 1.4-1.5, P < .05). CAD counts were also slightly higher in internal carotid than in vertebral artery (IRRs 1.168, 1.43, and 1.127, respectively). Neither systolic blood pressure nor pulse pressure was significantly associated with CAD counts.
  
  
  CONCLUSIONS
  CAD occurs more commonly in cooler months regardless of geographical location, suggesting transient seasonal causes may be important in the pathophysiology. This effect was slightly higher in internal carotid than in vertebral artery, suggesting differing trigger mechanisms between dissection sites.
authors.affiliation: Faculty of Health and Medicine, The University of Newcastle, New South Wales, Australia; School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: l.thomas2@uq.edu.au.
authors.forename: Lucy C
authors.initials: LC
authors.lastname: Thomas
authors.affiliation: Queen Elizabeth Hospital, Woodville, South Australia, Australia.
authors.forename: Lesley Ann
authors.initials: LA
authors.lastname: Hall
authors.affiliation: Faculty of Health and Medicine, The University of Newcastle, New South Wales, Australia; Hunter Medical Research Institute, Newcastle, New South Wales, Australia; John Hunter Hospital, New Lambton Heights, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Attia
authors.affiliation: Hunter Medical Research Institute, Newcastle, New South Wales, Australia.
authors.forename: Elizabeth G
authors.initials: EG
authors.lastname: Holliday
authors.affiliation: Stroke Research Group, Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Hugh S
authors.initials: HS
authors.lastname: Markus
authors.affiliation: Faculty of Health and Medicine, The University of Newcastle, New South Wales, Australia; Hunter Medical Research Institute, Newcastle, New South Wales, Australia; John Hunter Hospital, New Lambton Heights, Australia.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Levi
mesh_terms: D000328:Adult; D017677:Age Distribution; D001317:Austria / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D006113:United Kingdom / Q000453:epidemiology; D020217:Vertebral Artery Dissection / Q000175:diagnosis* / Q000453:epidemiology*; D055815:Young Adult
keywords: Cervical artery dissection; carotid; risk factors; seasonal variation; spontaneous; vertebral