Diffusion-weighted MRI abnormalities as a clue to the diagnosis of herpes simplex encephalitis

Herpes simplex virus (HSV)–1 encephalitis has an incidence of one to four cases per million people per year and accounts for up to 20% of all encephalitides. High morbidity and mortality without treatment underscores the importance of early diagnosis and therapy. CSF PCR analysis is the gold standard for diagnosis, with high sensitivity and specificity.1 In addition to PCR, the CSF profile and pattern of MRI abnormalities are also important clues to the diagnosis of HSV encephalitis. On MRI, T2 hyperintensities in medial temporal and inferior frontal lobes are commonly seen.1 Previous studies, primarily in neonates, suggest that diffusion-weighted imaging (DWI) is more sensitive than conventional MR sequences in detecting lesion extent.2-4⇓⇓ We report a case of HSV-1 encephalitis in an adult with nonspecific laboratory findings, negative initial PCR, and striking abnormalities on DWI compared with relatively normal T2-weighted images. A 52-year-old man presented with 1 day of aphasia and a seizure. History was significant for end-stage liver and renal disease. The patient followed commands, …