The prevalence of PTH was over 40% at all time points over the first year after TBI, which suggests that PTH is a frequent problem that continues long after the initial TBI. In addition, PTH is a widespread problem, with a cumulative incidence reaching 71% in this prospectively collected sample of participants. This high rate of headache over time has not been previously reported. Prior research has suggested lower prevalence rates of headache at 1 year, between 18% and 33% (van der Naalt et al., 1999
; Walker et al., 2005
), with only one study of veterans (who were mostly male), with rates of headache at 1 year of 40% (Walker et al., 2005
Our findings show that 28% of new headaches are reported after the initial evaluation, occurring at 6 and even 12 months-post injury. The ICHD criteria for a diagnosis of acute or chronic PTH requires that onset of headache must occur within 1 week of regaining consciousness after TBI; therefore the issue of any temporal relationship is important. Individuals with more moderate or severe TBI may not be responsive or able to verbalize pain due to headache within the first week after injury (Sherman et al., 2006
). Even the authors of the ICHD diagnostic criteria acknowledge the difficulty in distinguishing a high general population prevalence tension-type headache from PTH occurring weeks or months after trauma (The International Classification of Headache Disorders, 2004
). Our results are similar to those found by Theeler and Erickson (2009
), who examined the temporal association of headaches following mild head or neck trauma in a military population, and found that only 27% of headaches developed within a week post-trauma. Whether such classification, or misclassification, of headache after TBI is important is under debate. In its present form, a diagnosis of PTH does not rely on symptom criteria or provide direction for treatment. However, misclassification or missed diagnoses may underestimate the true incidence and prevalence of PTH, which could negatively impact treatment decisions as well as interfere with medico-legal issues in securing financial support for ongoing management of TBI.
In our sample, rates of PTH were high in all three severity groups, with no significant differences as a function of length of PTA. Further studies need to be conducted to confirm this finding in representative and prospectively studied groups of participants with a broad range of TBI severity. Our sample of “mild TBI” (i.e., PTA less than 1 day) contained only 25 participants (6% of the total participants) who were admitted for inpatient rehabilitation. These participants may be classified as having complicated mild traumatic brain injuries, as 24 of the 25 had GCS scores of 13–15, and 23 of the 25 had head CT abnormalities (Williams et al., 1990
). However, the presence of CT scan abnormalities would classify these injuries in the moderate-to-severe category in some classification systems (Malec et al., 2007
), making this sample more homogeneous and possibly limiting the extent to which differences in PTH incidence differ between injury severity classes. Prior research that has supported the idea of higher rates of headache in individuals with mild TBI has often focused on individuals presenting to outpatient clinics with a wide variation in time since injury and with varying presenting problems (Couch and Bearss, 2001
; Uomoto and Esselman, 1993
). While our mild group is likely more severely injured than those with mild TBI referred to in the literature, our rates of PTH with varying levels of severity of brain injury are similar and high. Our finding is consistent with the findings of a prior study which reported on rates of post-traumatic symptoms that included headache at 1 year in a prospectively studied group of participants with TBI with a broad range of TBI severity (Dikmen et al., 2010
). Future studies will need to include similar definitions of TBI severity as well as headache in representative and non-select cases.
Consistent with prior research, we found that a history of premorbid headache is significantly related to headache after TBI. This highlights the importance of assessment of premorbid headache as a risk factor for PTH, and may guide treatment options for physicians caring for individuals with TBI. In addition, females were found to have higher rates of headache, similar to the rates seen in the general headache literature (Jensen and Thulstrup, 2001
). In the current study, females were not only found to have higher rates of PTH overall, but also reported headache at all time points significantly more frequently than males. Whether this was related to hormonal changes or to other sex characteristics was not assessed, since such data were not collected. Future research is needed to examine whether these potential risk factors of sex and history of headache prior to injury may influence the treatment or diagnosis of PTH.
The current study does have limitations. First, all information about headache was collected by trained examiners using a standardized questionnaire in person (initial assessment), or over the phone (for follow-ups), and there was no physician evaluation. However, the headache questionnaire was developed by experts in headache and TBI to include relevant data similar to that which would be collected in a physician's office. Second, only participants who were hospitalized for rehabilitation were eligible for our study; therefore the sample may not be entirely representative of patients with TBI within this severity range in general. However, it is important to point out that subject selection was not related to pre- or post-injury headache.
Third, we cannot determine the effect of TBI as compared to injuries to other body parts with respect to headaches, as we did not have a non-head-injured trauma control group. Finally, information about the headaches was collected from proxies that knew the patient well pre- and post-injury in a fraction of the cases (15%), either due to the degree of neurologic impairment precluding valid testing at baseline, or lack of availability of the subject at follow-up evaluations. However, proxies tended to report headache less frequently than participants, and therefore our estimates of headache represent an underestimation of the likely rates of headache in our sample.
In summary, our data show that PTH is a frequent consequence of TBI and occurs in a much larger percentage of persons than previously reported. We found that 23% of participants reported headache at all time points over 1 year after injury, with 22–29% reporting frequent headaches (multiple times per week/daily). In contrast only 4–5% of persons with headaches in the general population endorse chronic daily headache (>15 days per month; Castillo et al., 1999
; Scher et al., 1998
; Silberstein and Lipton, 1994
). Finally, the severity of TBI, at least within the range represented in our sample, does not appear to determine the incidence of PTH. We found a similar rate of PTH across a range of PTA durations.
Future research is needed to determine the clinical characteristics of PTH. Our findings and future findings of clinical characteristics may have relevance for the development of a new classification scheme for PTH. Better understanding of the characteristics and natural history of PTH may provide us with a framework on which to study early, aggressive treatments to prevent or reduce the frequency of chronic PTH, and to alleviate suffering.