Application of the International Headache Society classification criteria in 652 cluster headache patients.

We applied the International Headache Society (IHS) classification coding parameters to a study population of 652 cluster headache (CH) patients, in order to determine how many patients did not fulfil the diagnostic criteria for group 3.1 and to find out any diagnostic elements that could be changed in the upcoming revision of the classification to make it more relevant to current clinical practice. Ninety-nine patients were found to have cluster-like disorder (3.3), including 74 (74.7%) who did not fulfil the diagnostic criteria for CH, because either pain was not associated with any of the accompanying autonomic phenomena listed in the classification or it was not located orbitally, supraorbitally and/or temporally. A review of our total sample showed that 72.0% of patients reported frontal and occipital pain location; in 61.8%, 33.4% and 39.1% of cases, attacks were also accompanied by restlessness/agitation, nausea and photophobia, respectively. In a coding system that took into account the diagnostic elements that we considered in our study, group 3.1 of the existing IHS classification would actually include 51 of the 99 patients currently coded as 3.3.