When a new headache occurs for the first time in close temporal relation to a known trauma, it is classified as a secondary headache attributed to the trauma. In the PTH, there has to be a close temporal relationship to the trauma. Thus, PTH has to begin within 7 days after injury to the head or after regaining consciousness. The 7-day interval is somewhat arbitrary and further research is needed to assess whether or not a different interval would be more appropriate. In the meantime, the ICHD-3 has also created appendix criteria for when the interval between injury and headache onset is greater than 7 days (delayed-onset headache attributed to traumatic injury to the head).

PTH is further divided into an acute and a persistent (previously called chronic) PTH. Acute PTH is defined as resolving within 3 months after the injury. Persistent PTH is defined as headache lasting more than 3 months after the injury (Table 17.1).

Both the acute and the persistent PTHs are then classified based upon the severity of the initial trauma in mild versus moderate and severe. There is no consensus about what characterizes the trauma that causes PTH except for the severity and the level of consciousness in the acute stage measured at the Glasgow Coma Scale. Within the trauma literature, multiple terms such as traumatic brain injury (TBI), head trauma, closed head injury, minor or minimal head injury, commotion or concussion have been applied and there is no clear consensus on the best term and definition. Still, there is also no evidence for an underlying brain injury after a mild injury to the head so the more descriptive term “head trauma” is consequently used in the following as in the opinion to the author we only have the history of a trauma to the head. For a clear debate and research strategy, the head trauma and the applied terms have to be clearly defined in the scientific community. More than 90 % of head trauma is classified as mild and the main body of literature is focused on PTH after a mild trauma.

The reason for these subdivisions is mainly practical as the underlying mechanisms most likely are different in the acute or persistent subforms. It seems also obvious for both patients and the society that a moderate or severe head trauma can cause headache whereas it is mystifying that a mild trauma, even without unconsciousness, can give rise to a debilitating persistent PTH. Several studies confirm the inverse relation between trauma severity and persistent PTH as patients with moderate to severe head trauma only rarely report persistent PTH.