Axial FLAIR MRI at the level of the medulla. Areas of inflammation in the brainstem and cerebellum adjacent to the 4th ventricle. Patient floridly symptomatic.
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Meningoencephalitis: Viral
Overview
Viral meningoencephalitis divides into:
- Acute, aseptic (presenting with severe headache but non-lethal symptoms).
- Encephalitis (with prominent confusion).
- Arthropod-borne encephalitis (those from insect bites).
- < 10 cells, 70% of which are lymphocytes
- Glucose is 60% of that of the serum glucose
- Protein is from 15 to 45
- CSF pressure is usually 70 to 180 mmH2O.
- Cell counts are typically from 50 to 250, the majority of cells are usually lymphocytes
- Glucose is often normal
- Protein is elevated
- Pressure is often normal
viral meningitis
Acute, aseptic
- Enterovirus is the most common (by far).
- Influenza was formerly the most common cause but now typically only manifests in those not vaccinated
- Lymphocytic choriomeningitis (LCM) is a rodent-borne disease.
- Herpes simplex virus type 2 causes Mollaret meningitis, which manifests with recurrent headaches and is treatable with acyclovir.
- HIV classically causes an aseptic meningitis as its first symptom, but this is often dismissed by patients.
Viral encephalitis
- Herpes simplex type 1, which manifests with a limbic encephalitis (medial temporal inflammation) and pathologic findings of Cowdry, Type A intranuclear inclusions in neurons and glia.
- CMV is an important congenital cause of meningitis (it's one of the TORCH syndromes) and also occurs, notably, in the immunosuppressed. On pathologic exam it demonstrates: owl-eye inclusions.
- PML occurs from a reactivation of JC virus in the immunosuppressed (notably from iatrogenic causes); it infects oligodendrocytes, so it causes demyelination.
- HIV – we learned that it causes an aseptic meningitis at presentation, but it also causes a chronic meningitis, which manifest with pathologic findings of microglial nodules and multinucleated giant cells.
- Measles, notably, can cause a chronic meningitis called: subacute sclerosing panencephalitis, which is a progressive encephalopathy.
We can group CMV, PML, HIV, and SSPE (measles) as leukoencephalopathies in that they typically manifest with white matter invasion (as specifically address with PML).
Arthropod-borne encephalitis
- Typically manifest with pathologic findings of perivascular cuffs of lymphocytes (meaning aggregation of lymphocytes around a blood vessel. And also microglial nodules.
- Western hemisphere:
- West Nile virus (which can manifest with encephalitis and also poliomyelitis (anterior horn cell disease – flaccid paralysis); Eastern Equine virus, Western Equine virus, St. Louis virus, and La Crosse virus.
- Far East
- Japanese B virus
- Eastern Europe and Russia
- Tick-borne virus.