Progressive multifocal leukoencephalopathy and multiple sclerosis: lessons from natalizumab.

Area of Science:

• Neuroimmunology
• Clinical Neurology
• Pharmacovigilance

Background:

• Natalizumab is used for autoimmune diseases like multiple sclerosis and Crohn's disease.
• Progressive multifocal leukoencephalopathy (PML) is a rare but serious opportunistic infection of the brain.
• The association between natalizumab and PML has raised safety concerns.

Purpose of the Study:

• To report three cases of PML in patients treated with natalizumab.
• To recommend revised entry and diagnostic criteria for clinical trials involving natalizumab.
• To inform treatment decisions for relapsing-remitting multiple sclerosis (RRMS) patients based on PML risk.

Main Methods:

• Case series review of three patients who developed PML during natalizumab therapy.
• Analysis of patient diagnoses, prognoses, and treatment outcomes.
• Literature review and risk-benefit assessment of natalizumab for RRMS.

Main Results:

• Three patients (one with RRMS, one with Crohn's disease, one with an unclear diagnosis) developed PML.
• The RRMS patient experienced severe, permanent neurological damage; the other two patients died.
• The cases highlight potential risks in specific patient populations and trial designs.

Conclusions:

• Revised criteria are needed to exclude patients with favorable prognoses or uncertain diagnoses from drug trials.
• Natalizumab should be used cautiously in RRMS patients with low risk of disability.
• Further data on natalizumab efficacy are required to guide treatment decisions for high-risk RRMS patients.