Individuals hospitalized for a head injury are more likely to have new onset and worsening of pre-existing headache and persistent headache, compared to general population. This supports the entity of the ICHD-3 beta diagnosis “persistent headache attributed to traumatic injury to the head”. 

For the global society, headache puts a major impact on the lives of individuals. The number of studies reported headache as a major cause of morbidity. After any head injury, headache is the most frequent symptom. The international classification of headache disorders defines headache attributed to head injury (HAIH) as a headache with no defining clinical characteristics that starts within seven days of injury. To investigate a causal relationship between the head injury and subsequent headache, a control group for comparison is vital, preferably through a population-based design. Until now, there are only two population-based, controlled studies on this subject, and their findings are inconsistent. Therefore, the primary aim of the current study was to analyze headache data for those who participated in both the second and third waves of the HUNT study. They evaluated the impact on the new-onset headache or exacerbation of headache due to head injuries in a population with known pre-injury headache status, considering the head injury severity.

Rationale behind the research:

None of the studies have succeeded to investigate the long-term follow-up of headache after the head injury.

Therefore, Nordhaug L H et al conducted this study to evaluate the impact of a new-onset headache due to head injuries.

Objective:

To analyze the headache data for those who participated in both the second and third waves of the HUNT Study, evaluating the impact on new onset headache or exacerbation of headache due to head injuries in a population with known pre-injury headache status, taking into account the head injury severity. 

Study outcome measures:

• The HUNT-surveys: The HUNT Study is a longitudinal cohort study in which all inhabitants ≥20 years of age in Nord-Trøndelag were invited to participate. Participants were examined three times. The two last surveys, HUNT2 (1995–1997) and HUNT3 (2006–2008) covered a large number of health-related items
• Headache categories: Both HUNT2 and HUNT3 questionnaires included the screening question “Have you suffered from headache during the last 12 months?” The answers to the screening questions were used to categorize the responders into four mutually exclusive groups with regard to headache suffering at two time points: Stable non-sufferers (headache-free in both studies), past sufferer (headache in HUNT2 but not in HUNT3), stable headache sufferer (headache in both studies) and new sufferer (headache in HUNT3, but not in HUNT2).
• Head injury data collection: All participants who had answered the headache screening question in HUNT3 and who had also been hospitalized in the region due to a head injury during the period 1988–2008 were identified in 2012 by a computer-based search. Information regarding the head injuries was collected from medical records. If the same individual had more than one head injury within the period, up to three of the most recent head injuries were recorded. The head injuries were classified according to the Head Injury Severity Scale (HISS).
• Other measurements: The HUNT2 and HUNT3 surveys included many health related items. In addition to headache, the present study used information about the participants age, sex, duration of education, smoking habits, total Hospital Anxiety and Depression Scale (HADS) score, self-reported health, body-mass index (BMI) and Modified Norwegian version of the CAGE alcohol-screening instrument (CAGE) score.

Time period: Write the time period at which outcomes were studied like baseline, 2 weeks and 6 weeks 

Figure 1: Flow of participants through the HUNT2 and HUNT3 study and selection of head injury patients

Study Outcomes

• Head injuries: Among the 294 individuals with head injuries, 11 experienced two head injuries, adding up to a total of 305 incidents. Considering only the first head injury (of those with more than one), 11.9% of the head injuries were minimal, 71.8% were mild, 10.9% were moderate and 5.4% were unclassifiable. There were no severe head injuries reported in the survey. The most common cause of injury was falling (55.1%), followed by traffic accidents (28.6%) and assault (1.7%). A computed tomography (CT) scan was performed in 56.4% (n=172), an MRI in 1.0% (n=3) and a plain X-ray of the head in 3.6% (n=11) of the cases. The scans revealed traumatic pathology in 16.0% (n=47). In total, 9.2% (n=27) of all patients had intracranial pathology 9.9% (n=29) had cranial fractures (revealed either by imaging or clinical findings), and 5.1% (n=15) had both cranial fracture and intracranial pathology.
• Headache categories: Among the 25,956 participants, 12,830 (49.4%) were headache free in HUNT2 and HUNT3 (stable nonsuffering), 6303 (24.3%) suffered from headache in both surveys (stable headache suffering), 4523 (17.4%) reported headache in HUNT2 only (past headache suffering) and 2300 participants (8.9%) had no headache in HUNT2 but reported to suffer from headache in HUNT3 (new headache suffering)
• Among 129 participants with head injury and preexisting headache, 46 (35.7%) suffered from migraine, 57 (44.2%) from non-migrainous headache and 26 (20.2%) were unclassifiable
• Individuals with mild head injury were more likely to have new onset of headache (OR 1.74, 95% CI 1.05–2.87) and stable headache suffering (OR 1.70, 95 CI 1.15–2.50) compared to controls
• There were no significant associations between head injury and past headache suffering or improvement of headache status. No consistent significant interaction was observed between head injury and any of the covariates. The only significant interaction observed was for smoking and only in the case of improvement of headache.

This study presents the population-based data on headache occurrence after the head injury. The findings of our study suggested that exposure to head injury increases the risk of new-onset headache suffering. The data was analyzed concerning sex differences; however, any significant difference between males and females in the effect of a head injury on the change in headache status from HUNT2 to HUNT3 was not reported. Previous studies showed an inverse dose-response relationship between the severity of head injuries and persistent headache. The present study estimated that seriousness of headache after a mild head injury was higher than with the moderate head injury. This indicates that patients with previous mild head injuries are more prone to headache.

The large population-based dataset on headache is the key strength of this study. Moreover, its extensive objective information collected from medical records eliminated the bias regarding the head injury and helped to classify the head injuries according to severity. Validation of the severity of headache before and after the head injury enabled to compare prevalence and frequency of headache before and after the time of the head injuries in this study. This study also eliminates recall bias, also regarding pre-study headache suffering, as participants might tend to trivialize headache before the head injury because they understand their headache as a consequence of their head injury. Such possible under-reporting of pre-injury headache could be the reason why several prospective studies report pre-injury headache prevalence far below known headache prevalence in the general population. 

Individuals hospitalized for a mild head injury were more likely to develop new headache suffering or report exacerbation of previously documented headache compared to the surrounding general population. Hence, the present study substantiates HAIH as a true secondary headache entity and not a primary headache misattributed to head injury.