Primary or secondary headache or both?
When a headache occurs for the first time in close temporal relation to a non-vascular intracranial disorder, it is coded as a secondary headache attributed to that disorder. This remains true when the new headache has the characteristics of any of the primary headache disorders classified in Part One of ICHD-3 (beta). When a pre-existing headache with the characteristics of a primary headache disorder becomes chronic, or is made significantly worse (usually meaning a two-fold or greater increase in frequency and/or severity), in close temporal relation to a non-vascular intracranial disorder, both the initial headache diagnosis and a diagnosis of 7. Headache attributed to non-vascular intracranial disorder (or one of its subtypes) should be given, provided that there is good evidence that the disorder can cause headache.
In this chapter are the headaches attributed to changes in intracranial pressure. Both increased and decreased cerebrospinal fluid (CSF) pressure can lead to headache. Other causes of headache here are non-infectious inflammatory diseases, intracranial neoplasia, seizures, rare conditions such as intrathecal injections and Chiari malformation type I, and other non-vascular intracranial disorders.
Compared to those on primary headaches, there are few epidemiological studies of these headache types. Controlled trials of therapy are almost non-existent.
For headache attributed to any of the non-vascular intracranial disorders listed here, the diagnostic criteria include whenever possible:
A. Headache fulfilling criterion C
B. A non-vascular intracranial disorder known to be able to cause headache has been diagnosed
C. Evidence of causation demonstrated by at least two of the following:
1. headache has developed in temporal relation to the onset of the non-vascular intracranial disorder
2. either or both of the following:
a) headache has significantly worsened in parallel with worsening of the non-vascular intracranial disorder
b) headache has significantly improved in parallel with improvement in the non-vascular intracranial disorder
3. headache has characteristics typical for the non-vascular intracranial disorder
4. other evidence exists of causation
D. Not better accounted for by another ICHD-3 diagnosis.
Headache persisting for more than one month after successful treatment or spontaneous resolution of the intracranial disorder usually has other mechanisms. Headache persisting for more than three months after treatment or remission of intracranial disorders is defined in the Appendix for research purposes. Such headache exists but has been poorly studied; Appendix entries are intended to stimulate further research into such headaches and their mechanisms.