Posterior reversible encephalopathy syndrome as a multiple sclerosis relapse mimic during interferon therapy

Posterior reversible encephalopathy syndrome is a rare syndrome involving the subcortical cerebral white matter. We describe the case of a 63-year-old male patient with relapsing remitting multiple sclerosis under interferon beta therapy and acute onset of atypical unilateral posterior reversible encephalopathy syndrome mimicking a relapse. This case highlights the importance of clinical suspicion for multiple sclerosis mimics, namely in older patients, which may need disease modifying treatment suspension and directed treatment in order to achieve better clinical prognosis.