Applying the International Classification of Headache Disorders to the emergency department: an assessment of reproducibility and the frequency with which a unique diagnosis can be assigned to every acute headache presentation.

STUDY
OBJECTIVE: Although almost 2 decades have passed since the International Headache Society first introduced its International Classification of Headache Disorders (ICHD), the applicability of this classification scheme in the emergency department (ED) has not been assessed. As a first step toward identifying the role the ICHD should play in the ED, we address 2 questions: Can a structured interview and adherence to the ICHD allow ED headache patients to be classified in a reproducible manner? With the ICHD, how often can one specific diagnosis be assigned to each ED headache presentation?
METHODS: This was a structured interview and medical record review of patients with nontraumatic headache, performed in an urban ED from March 2004 through August 2005. Using the data from the interview and the subject's ED record, 2 emergency medicine investigators independently classified each of the headaches twice: first, to determine presence or absence of a primary headache disorder, and then to determine presence or absence of a secondary headache disorder. If a primary headache was present, it was further classified as migraine, tension-type headache, trigeminal autonomic cephalalgia, chronic daily headache, or primary headache unclassifiable. Interobserver discordance was adjudicated by an experienced headache specialist.
RESULTS: Four hundred eighty patients were enrolled in the study. The emergency medicine investigators had a high level of interobserver agreement on secondary headaches (agreement 94% [95% confidence interval (CI) 92% to 96%]) and primary headaches (agreement 91% [95% CI 88% to 93%]). Among the 480 subjects, 122 (25%) had a secondary headache disorder, 309 (64%) had a primary headache disorder, 49 (10%) had a coexisting primary and secondary headache, and for 95 (20%) subjects, neither a primary nor a secondary headache could be diagnosed. Of 309 subjects with a primary headache, 186 (60%) had migraine, 34 (11%) had tension-type headache, 2 (1%) had trigeminal autonomic cephalalgia, and 77 (26%) had an unclassifiable primary headache. Overall, a specific ICHD headache diagnosis could not be assigned to 36% of subjects either because a specific primary headache disorder could not be identified or because neither a primary nor a secondary headache disorder could be diagnosed.
CONCLUSION: Although a detailed structured interview in the ED and adherence to the ICHD resulted in reproducible classification of headache patients, more than one third of acute headache patients could not readily be given a specific ICHD diagnosis in the ED.