Olfactory dysfunction following herpetic meningoencephalitis

Herpetic meningoencephalitis (HME) is a rare but often lethal herpes simplex infection. Patients who survive generally retain neurological deficits. The literature consists mostly of autopsy reports and consistently shows the peripheral and central olfactory pathways to be severely damaged. Little information is available on degree and recovery of olfactory impairment following HME. In this retrospective case series, three patients (two women, one man) who had survived HME were tested with standardized olfactory tests (Sniffin' Sticks) and were followed up more than 3 years after the infectious episode. Initially, all patients showed bilateral functional anosmia and no patient recovered normal olfactory function. Despite total smell loss, various patterns of olfactory deficits were found, with one patient having difficulty identifying odors despite present odor detection thresholds, and two patients lacking odor threshold detection ability. In conclusion, the present findings show that olfactory function is often permanently damaged in patients who have had HME. Lesions lead to various patterns of olfactory loss. Together with histological and clinical data from the literature this suggests further that the olfactory pathway plays a major role in the spread of herpetic meningoencephalitis. It also raises the question whether the olfactory epithelium serves as an entry into the brain for other pathogens.