Cluster-like headache. A comprehensive reappraisal.

Among the primary headaches, cluster headache (CH) presents very particular features allowing a relatively easy diagnosis based on criteria listed in Chapter 3 of the International Classification of Headache Disorders (ICHD-II). However, as in all primary headaches, possible underlying causal conditions must be excluded to rule out a secondary cluster-like headache (CLH). The observation of some cases with clinical features mimicking primary CH, but of secondary origin, led us to perform an extended review of CLH reports in the literature. We identified 156 CLH cases published from 1975 to 2008. The more frequent pathologies in association with CLH were the vascular ones (38.5%, n = 57), followed by tumours (25.7%, n = 38) and inflammatory infectious diseases (13.5%, n = 20). Eighty were excluded from further analysis, because of inadequate information. The remaining 76 were divided into two groups: those that satisfied the ICHD-II diagnostic criteria for CH, 'fulfilling' group (F), n = 38; and those with a symptomatology in disagreement with one or more ICHD-II criteria, 'not fulfilling' group (NF), n = 38. Among the aims of this study was the possible identification of clinical features leading to the suspicion of a symptomatic origin. In the differential diagnosis with CH, red flags resulted both for F and NF, older age at onset; for NF, abnormal neurological/general examination (73.6%), duration (34.2%), frequency (15.8%) and localization (10.5%) of the attacks. We stress the fact that, on first observation, 50% of CLH presented as F cases, perfectly mimicking CH. Therefore, the importance of accurate, clinical evaluation and of neuroimaging cannot be overestimated.