Post-infectious encephalitis in adults: diagnosis and management

Abstract

Many important central nervous system (CNS) syndromes can develop following microbial infections. The most severe forms of post-infectious encephalitis include acute disseminated encephalomyelitis (ADEM), acute hemorrhagic leukoencephalitis and Bickerstaff's brainstem encephalitis. ADEM is an inflammatory demyelinating disorder of the CNS. It typically follows a minor infection with a 2-30 days latency period and is thought to be immune-mediated. It is clinically characterized by the acute onset of focal neurological signs and encephalopathy. Patients can require intensive care unit admission because of coma, seizures or tetraplegia. Cerebrospinal fluid analysis usually shows lymphocytic pleocytosis but, unlike viral or bacterial encephalitis, no evidence of direct CNS infection is found. There are no biologic markers of the disease and cerebral magnetic resonance imaging is essential to diagnosis, detecting diffuse or multifocal asymmetrical lesions throughout the white matter on T2- and FLAIR-weighted sequences. High-dose intravenous steroids are accepted as first-line therapy and beneficial effects of plasma exchanges and intravenous immunoglobulins have also been reported. Outcome of ADEM is usually favorable but recurrent or multiphasic forms have been described.

Figure 1

Acute disseminated encephalomyelitis: FLAIR-weighted images (top panel) obtained in a 55-year-old patient admitted to the ICU for fever and impaired consciousness. CSF analysis showed evidence of aseptic meningitis. Note a characteristic pattern of extensive and diffuse hyperintense lesions affecting the brainstem and supratentorial regions with a comparatively small mass effect. Lesions not only affect the white matter but also para-hippocampal gyrus, left thalamus and typically cross over the corpus callosum. In the same patient (bottom), isotropic diffusion (b) is less sensitive than T2 FLAIR sequences (a), showing hyperintensities with a non-specific increased ADC (not shown). Note also partial “open-ring” enhancement on T1-weighted post-contrast corresponding image (c).

Figure 2

Acute disseminated encephalomyelitis: T2-weighted image obtained in a 42-year-old patient admitted to the ICU for bilateral diaphragmatic palsy 8 days after an acute myelopathy. Spinal cord hyperintensity and swelling involving more than 3 segments (white arrows). Corpus callosum hyperintensity and swelling (black arrow).

Figure 3

Algorithm proposed for the initial management of acute forms of encephalitis admitted to the intensive care unit (adapted from Refs. 34, 36).