Headache caused by viral meningitis or encephalitis, typically with neck stiffness and fever and variably associated, according to the extent of the infection, with neurological symptoms and/or signs including changes in mental state.
A. Any headache fulfilling criterion C
B. Viral meningitis or encephalitis 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 viral meningitis or encephalitis
2. headache has significantly worsened in parallel with worsening of the viral meningitis or encephalitis
3. headache has significantly improved in parallel with improvement in the viral meningitis or encephalitis
4. headache is either or both of the following:
b) located in the nuchal area and associated with neck stiffness
D. Not better accounted for by another ICHD-3 diagnosis.
9.1.2 Headache attributed to viral meningitis or encephalitis should be suspected whenever headache is associated with fever, stiff neck, light sensitivity, nausea and/or vomiting.
Enteroviruses account for most cases of 9.1.2 Headache attributed to viral meningitis or encephalitis; Herpes simplex, adenovirus, mumps and others may also be responsible. CSF polymerase chain reaction (PCR) gives the specific diagnosis in the majority of cases. Positive CSF PCR for Herpes simplex virus (HSV) types 1 or 2 and serology for HSV-1&2 DNA presume the diagnosis of Herpes simplex encephalitis. In some cases, CSF PCR is positive for Human Herpes virus (HHV) types 6 or 7. It has been documented that PCR sensitivity is reduced by more than half when the test is performed one week after the onset of the symptoms, causing false negatives. When PCR performed after one week is negative, the diagnosis can be made on the basis of an altered CSF/blood antibody ratio.
As with 9.1.1 Headache attributed to bacterial meningitis or meningoencephalitis, it may be difficult to distinguish involvement purely of the meninges from involvement purely of the encephalon. The distinction is nonetheless important to make and maintain, because the two conditions differ prognostically, the expectation being worse with encephalitic involvement. For this reason, separate criteria are given for 188.8.131.52 Headache attributed to viral meningitis and 184.108.40.206 Headache attributed to viral encephalitis.
Also at variance from 9.1.1 Headache attributed to bacterial meningitis or meningoencephalitis, a persistent post-infectious subform of 9.1.2 Headache attributed to viral meningitis or encephalitis is not supported by evidence and has not, therefore, been contemplated.