Multiple sclerosis: role of meningeal lymphoid aggregates in progression independent of relapse activity

Area of Science:

• Neuroimmunology
• Neurology
• Pathology

Background:

• Current multiple sclerosis (MS) classification (relapsing-remitting MS and progressive MS) may not fully capture disease progression.
• Progression independent of relapse activity (PIRA) is a significant clinical phenomenon in MS, evident early and worsening with age.
• Understanding PIRA mechanisms is crucial for developing effective MS therapies.

Purpose of the Study:

• To shift focus from categorical MS classifications to the clinical phenomenon of PIRA.
• To elucidate the underlying mechanisms of PIRA, including chronic-active lesions (CALs) and meningeal inflammation.
• To explore the role of autonomous meningeal lymphoid aggregates in driving PIRA and tissue injury.

Main Methods:

• Review of existing literature on MS pathogenesis and clinical progression.
• Focus on the phenomenon of PIRA and its early onset in the disease course.
• Integration of recent findings on specialized MRI characterization of CALs as paramagnetic rim lesions.

Main Results:

• PIRA is a continuous process throughout MS, becoming more apparent with patient aging.
• Key PIRA mechanisms include chronic-active demyelinating lesions (CALs), subpial cortical demyelination, and nerve fiber injury.
• Autonomous meningeal lymphoid aggregates are proposed as a primary driver of PIRA, existing pre-disease and evading current treatments.

Conclusions:

• PIRA represents a critical aspect of MS symptomatic worsening, necessitating a move beyond traditional classifications.
• Chronic-active lesions, identified via specialized MRI, serve as a radiographic biomarker for PIRA.
• Targeting meningeal inflammation and CALs holds promise for future MS therapeutic strategies to address PIRA.