RESUMO
Background Clear definitions of study populations in clinical trials may facilitate application of evidence to clinical populations. This review aimed to explore definitions of study populations in clinical trials on migraine, tension-type headache, cluster headache, and cervicogenic headache. Methods We performed a systematic review of clinical trials investigating treatment efficacy for migraine, tension-type headache, cluster headache, and cervicogenic headache. We extracted data on diagnosis, inclusion criteria and baseline headache characteristics. Results Of the 229 studies reviewed, 205 studies (89.5%) defined their populations in adherence to the International Classification of Headache Disorders (ICHD) criteria. Some studies ( n = 127, 55.5%) specified diagnosing through interview, clinical examination and diary entry. The most commonly reported inclusion criteria were pain intensity for migraine and tension-type headache studies ( n = 123, 66.1% and n = 21, 67.7%, respectively), episode frequency ( n = 5, 71.4%) for cluster headache studies, and neck-related pain for cervicogenic headache studies ( n = 3, 60%). Few studies reported details on the extent to which diagnostic criteria were present at baseline. Conclusions ICHD is routinely used in defining populations in headache studies. Details of baseline headache characteristics were not as consistently reported.