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A syndrome characterized by daily episodes of intense periorbital pain that recur over a period of 6-12 weeks that may be followed by a period of remission of months to years. The pain is non-throbbing, has a duration of 30-60 minutes and tends to occur at night or at regular intervals during the day. Unilateral rhinorrhea, conjunctival injection, lacrimation, facial flushing, and miosis frequently accompany the headaches, which primarily affect young adult males. (Adams et al., Principles of Neurology, 6th ed, p181)