title: Pathophysiology of hypnic headache.
abstract: BACKGROUND
  Hypnic headache (HH) is a rare primary headache disorder that is characterized by strictly sleep related headache attacks.
  
  
  OBJECTIVE
  The underlying pathophysiology of HH is mainly enigmatic but some clinical characteristics such as circadian rhythmicity and caffeine responsiveness may point toward possible underlying mechanisms.
  
  
  METHODS
  Current studies that deal with the pathophysiology of HH are summarized. Data on cerebral imaging, sleep, electrophysiology studies, effectiveness of drugs, and symptomatic headache types are discussed to illuminate underlying pathophysiologic mechanisms.
  
  
  CONCLUSIONS
  HH can be clearly differentiated by its clinical presentation as well as imaging and electrophysiological study results from other primary headaches such as migraine or cluster headache. The underlying pathophysiology is still enigmatic but a hypothalamic involvement seems to be likely.
authors.affiliation: Department of Neurology and Westgerman Headache Center Essen, University Duisburg-Essen, Germany dagny.holle@uk-essen.de.
authors.forename: Dagny
authors.initials: D
authors.lastname: Holle
authors.affiliation: Department of Neurology and Westgerman Headache Center Essen, University Duisburg-Essen, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Naegel
authors.affiliation: Department of Neurology and Westgerman Headache Center Essen, University Duisburg-Essen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Obermann
mesh_terms: D051270:Headache Disorders, Primary / Q000503:physiopathology*; D006801:Humans
keywords: Hypnic headache; caffeine; hypothalamus; indomethacin; sleep