Progressive multifocal leukoencephalopathy in dimethyl fumarate-treated multiple sclerosis patients

Area of Science:

• Neuroimmunology
• Demyelinating Diseases
• Infectious Neuropathology

Background:

• Dimethyl fumarate (DMF) is a widely prescribed oral therapy for relapsing multiple sclerosis (MS).
• Progressive multifocal leukoencephalopathy (PML) is a rare opportunistic infection associated with several disease-modifying therapies (DMTs) for MS.
• Understanding PML risk factors in DMF-treated patients is crucial for patient safety.

Purpose of the Study:

• To detail the clinical characteristics of nine PML cases in patients treated with DMF.
• To assess the incidence of PML in DMF-treated MS patients.
• To identify potential risk factors and biomarkers for PML in this population.

Main Methods:

• Retrospective review of nine PML cases in patients receiving DMF for MS.
• Calculation of PML incidence based on case data.
• Analysis of clinical characteristics, including age, lymphopenia, and absolute lymphocyte counts (ALCs).
• Discussion of DMF's immunomodulatory mechanisms, including effects on immune cell migration.

Main Results:

• PML incidence in DMF-treated patients was determined to be 0.02 per 1000.
• Persistent severe lymphopenia and older age were identified as potential risk factors for PML.
• PML occurred in some patients with ALCs above established thresholds, suggesting the importance of specific lymphocyte subset changes.
• DMF's mechanism of decreasing immune cell migration may involve altered expression of adhesive molecules.

Conclusions:

• DMF-associated PML, though rare, requires careful monitoring.
• Factors beyond total ALC, such as specific lymphocyte subsets and cerebrospinal fluid (CSF) immune profiles, may be important for risk assessment.
• Further research into DMF's immunomodulatory effects is needed to refine PML risk stratification and patient management strategies.