PML can present in many ways so any new neurological symptoms in patients on natalizumab should be evaluated by an experienced neurologist. But often the earliest symptoms are cognitive and can consist of word finding difficulty, memory dysfunction, confusion, followed by gait ataxia, vision problems, etc.
Even though a patient is JCV antibody negative, he should still be evaluated for PML if any new symptoms or worsening of old symptoms. We must remain vigilant. Particularly now that treatments are also improving for PML.
I hope this helps.
Timothy Vollmer, MD
Professor of Neurology
Co-Director-RMMSC at Anschutz