MRI Deterioration in Herpes Simplex Encephalitis Despite Clinical Recovery

Objectives: Herpes simplex virus type 1 is a sporadic cause of viral encephalitis. Relapse of encephalitis occurs in up to 10% of patients, manifested by recurrent symptoms, clinical and MRI findings, and the presence of herpes simplex virus type 1 DNA in the cerebrospinal fluid (CSF). Methods: We describe the clinical features, MRI findings and outcome in 2 patients with herpes simplex encephalitis during the acute phase and 6 months after the onset of encephalitis. Results: Both patients had a good response to treatment and an excellent recovery. Despite clinical recovery, in a 6-month follow-up MRI lesions consistent with recurrence were disclosed, without any clinical findings or CSF abnormalities. Conclusions: The mechanism underlying this MRI deterioration is unclear and an immune-mediated mechanism may be involved. Thus, MRI deterioration after herpes simplex encephalitis should be interpreted with caution and it does not always represent a relapse, especially when the imaging studies do not correlate with the clinical and CSF findings.