Cytomegalovirus (CMV) encephalitis is a CNS infection that almost always develops in the context of profound immunosuppression.
This article focus on adult infection, CMV is also one of the most frequent prenatal infections. Please, refer on congenital CMV infection for further discussion on this specific entity.
It is extremely rare to involve immunocompetent individuals.
Presentation is variable, however generalised cognitive decline is most frequent. Focal neurological signs and cranial nerve palsies are uncommon to rare.
At autopsy active CMV infection is also seen systemically although clinical manifestations are variable:
- CMV adrenalitis (92%)
- CMV pneumonitis (42%)
- CMV retinitis (58%)
Typically, before CMV infections become clinically apparent the patient's CD4+ count typically reaches below 50/mm 2. CMV infects the entire neuraxis (brain, spinal cord, meninges, nerve roots, eye) and therefore has variable presentation.
Cytomegalovirus is a DNA virus belonging to the herpesviruses group, and is also known as Human Herpesvirus 5 (HHV-5). It is found in all geographic locations and socioeconomic groups, and infects between 50-80% of adults in the United States as indicated by the presence of antibodies in much of the general population.
Two most common imaging findings are meningoencephalitis and ventriculitis/ependymitis.
In CMV encephalitis, there is usually only non specific increased T2/FLAIR signal in the white matter. If ventriculitis is also present then enhancement of the ependymal surface and hydrocephalus may also be seen.
high T2 white matter change most prominent in a periventricular distribution
- no enhancement (unless ventriculitis present, in which case 30% or so will enhance)
- no mass effect (often seen with concurrent atrophy)
Appearances are similar to HIV encephalitis, although usually CMV occurs in patients with a longer duration of disease, and lower CD4+ counts.
Other white matter changes in HIV, especially :
- HIV encephalitis
- progressive multifocal leukoencephalitis (PML)
- primary CNS lymphoma: periventricular but has mass effect and enhances
Particularly in a profoundly immunocompromised patient, ventriculitis characterised by high T2/FLAIR signal and post contrast enhancement is highly suggestive of CMV infection.
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