9. Headache attributed to infection

Coded elsewhere:
Headache disorders attributed to extracranial infections of the head (such as ear, eye and sinus infections) are coded as subtypes of 11. Headache or facial pain attributed to disorder of the cranium, neck, eyes, ears, nose, sinuses, teeth, mouth or other facial or cervical structure.

General comment

Primary or secondary headache or both?
When a headache occurs for the first time in close temporal relation to an infection, it is coded as a secondary headache attributed to that infection. 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 an infection, both the initial headache diagnosis and a diagnosis of 9. Headache attributed to infection (or one of its subtypes) should be given, provided that there is good evidence that that infection can cause headache.

Acute, chronic or persistent?
9. Headache attributed to infection is usually the consequence of active infection, resolving within 3 months of eradication of the infection. In some cases, depending on the pathogenic agent, the infection cannot be treated effectively and remains active. The headache in these cases may not abate, because the cause remains present, and after three months is referred to as chronic. In other, rarer cases, the infection resolves or is eradicated but the headache does not remit; after three months, such headache is termed persistent (in keeping with other secondary headaches). Accordingly, acute and chronic subforms of headache attributed to active or recent infection have been defined, in some cases in contrast to persistent subforms of post-infectious headache (see for example 9.1.1.1 Acute headache attributed to bacterial meningitis or meningoencephalitis, 9.1.1.2 Chronic headache attributed to bacterial meningitis or meningoencephalitis and 9.1.1.3 Persistent headache attributed to past bacterial meningitis or meningoencephalitis). The purpose is to distinguish and keep separate two probably different causative mechanisms and two different management approaches.

Introduction
Headache is a common accompaniment of systemic viral infections such as influenza. It is also common with sepsis; more rarely it may accompany other systemic infections.

In intracranial infections, headache is usually the first and the most frequently encountered symptom. Occurrence of a new type of headache which is diffuse and associated with focal neurological signs and/or altered mental state, a general feeling of illness and/or fever should direct attention towards an intracranial infection even in the absence of neck stiffness. Unfortunately, there are no good prospective studies of the headaches associated with intracranial infection and the diagnostic criteria for some of the subtypes of 9.1 Headache attributed to intracranial infection are at least partly reliant upon expert consensus (including the views of experts in neuroinfection) when evidence is lacking.

The general criteria for this chapter, adhered to as far as possible, are as follows:
A. Headache fulfilling criterion C
B. An infection, or sequela of an infection, 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 infection
    2. either or both of the following:

      a) headache has significantly worsened in parallel with worsening of the infection
      b) headache has significantly improved or resolved in parallel with improvement in or resolution of the infection

    3. headache has characteristics typical for the infection

D. Not better accounted for by another ICHD-3 diagnosis.