Epidemiology and classification of post-traumatic headache: What do we know and how do we move forward? Comment on Lucas et al., “Prevalence and characterization of headache following mild TBI”

In this issue of Cephalalgia, Lucas et al. report on the natural history of headache following mild traumatic brain injury (TBI) in a civilian patient population. This interesting study adds to the growing body of knowledge related to the prognosis and characteristics of post-traumatic headache (PTH). It is also one of only a few studies on head-injured patients that classified headaches using standardized diagnostic criteria over multiple time points, so it is of particular interest. Study subjects consisted of 212 patients (76% male, mean age 44) at one level 1 trauma center. Subjects were enrolled within one week of sustaining a mild TBI (concussion), most often due to a motor vehicle accident (58%) or fall (24%). Interviews were initially conducted face to face and then by telephone up to one year after the injury. Subjects with ‘‘new or worse’’ headaches compared to before the injury were considered to have PTH. Headaches were classified as migraine, probable migraine, tension-type, and cervicogenic. Previous studies by this team (1,2) were based on a cohort of Veterans Administration (VA) rehabilitation patients with a wider range of head injury severity although used similar headache classification methodology. The primary findings of the present study were that a) between 54% and 69% of subjects reported new/ worse headaches at each interview although a smaller number (41%) reported this consistently at all interviews; b) of those reporting headache, the predominant subtype at three months was tension-type (37%) followed by probable migraine (25%) and migraine (24%); and c) peak incidence of new/worse headache was at the baseline (< 1 week post-injury) and first follow-up (three months post-injury) interviews. Several questions naturally flow from this and other recent studies. 1) What is the expected incidence of PTH and to what extent can we attribute this to the injury per se? In the present study, new-onset headache in general and migraine-like headache in particular were clearly more likely in these patients with head injuries than would be seen in an ageand gender-equivalent nonclinical population. For example, the one-year incidence of International Classification of Headache Disorders (ICHD) migraine in men in the general population has been reported to be less than 1 per 100 person years (3) although the incidence of subjectively worsened headache is unknown. What would be the expected incidence of ICHD migraine in a comparable ‘‘at-risk’’ population such as (for the present study) a predominantly male inpatient population with recent injuries of comparable severity not involving the head? It is possible, even likely, that an injured control group without head injuries would have a higher than expected incidence of headache for a variety of plausible reasons. The reality is that it is difficult to find truly ‘‘comparably injured’’ control groups without head injuries and then there is the added issue of generalizability and overmatching even when available. The few (to our knowledge) prospective studies of TBI patients