The Common Vein Copyright 2010
Herpes encephalitis is an infection of the cerebral hemispheres, brainstem or cerebellum by a herpes simplex virus.
HSV1 encephalitis is due to virus replication in previously quiescent cephalic sensory ganglia. It is responsible for most of the necrotic encephalitis, both in adults and children. HSV2 encephalitis affects the neonate or infant, with transmission happening during the passage through the birth canal during delivery.
In HSV1 encephalitis, necrotic lesions predominate in the anterior temporal lobes. This location explains the frequency of certain clinical symptoms.
Clinically, there is a sub-acute onset, with behavioral changes and language disorders, accompanied by a flu-like illness. Patients have high fevers, and later, change in mental status and possibly coma. Neck rigidity is seen in less than half of cases. Neurologically, aphasia or amnesia are important clues for the diagnosis of herpes encephalitis; paresis and other focal deficits are also possible, including seizures.
Diagnosis is made with analysis of the CSF, with lymphocytic predominance. PCR amplification is very specific.
Radiologically, MRI is often abnormal, even at an early stage. The lesions predominate in the medial and anterior temporal lobes and may extend to the insula, and are better seens as hyperintense T2 signals in the white matter of these structures; they are enhanced by contrast. They are well demonstrated on coronal sections.
Treatment is urgent and consists of IV administration of acyclovir.