How does the International Headache Society (IHS) classify episodic and chronic cluster headache (CH)?

Updated: Jun 07, 2019
  • Author: Michelle Blanda, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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The International Headache Society (IHS) classifies CH as episodic or chronic on the basis of duration as follows [3] :

  • Episodic CH occurs in periods lasting from 7 days to 1 year; cluster attacks are separated by pain-free intervals at least 1 month long

  • Chronic CH persists for more than 1 year either without remission or with remissions shorter than 1 month; it is further divided into 2 subcategories, chronic CH from onset and chronic CH evolving from episodic CH

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