Does natalizumab treatment increase the risk of herpes simplex encephalitis in multiple sclerosis? Case and discussion.

This report presents the 4th documented case worldwide of herpes simplex encephalitis in multiple sclerosis (MS) patients treated with natalizumab and the first case in the UK. Natalizumab is licensed for relapsing remitting multiple sclerosis in patients with high disease activity despite treatment with interferon-beta and patients with rapidly evolving severe, multiple sclerosis. Natalizumab is a monoclonal antibody targeted against alpha-4 integrin. Its proposed mechanism is attenuation of the migration of immune cells into the central nervous system. Reactivation of the JC virus causing progressive multifocal leucoencephalopathy (PML) and its association with natalizumab is well documented. This case adds support to the suggestion that natalizumab also increases the reactivation risk of CNS herpes simplex infection. A 34 year old woman was admitted with a generalized tonic-clonic seizure, fever and confusion following her 40th infusion of natalizumab. MRI demonstrated increased signal in the medial temporal lobes and EEG showed focal sharp waves over the temporal lobe. CSF PCR later confirmed herpes simplex virus. The patient made an eventual excellent recovery following 21 days of intravenous acyclovir therapy followed by 14 days of oral treatment.