Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) that often leads to substantial neurological disability, particularly in young adults (Compston and Coles, 2002). A key biomarker for MS diagnosis is the presence of oligoclonal bands (OCBs) in cerebrospinal fluid (CSF), which indicates intrathecal inflammation and immune activation (Villar et al., 2005). CSF analysis at the time of diagnosis provides valuable insights into CNS immune processes and supports differential diagnosis in demyelinating diseases (Link and Huang, 2006).

Routine CSF tests include evaluation of OCBs, IgG index, albumin ratio, and cell count. OCBs are detected in approximately 95 % of MS patients (Tumani et al., 2011). These bands represent clonally expanded immunoglobulin G and are considered highly indicative of intrathecal immune activity. Among the various patterns, Type 2 OCBs (present only in CSF) and Type 3 OCBs (present in both CSF and serum, but more intense in CSF) are the most relevant in MS diagnosis, reflecting the degree of CNS-restricted IgG synthesis (Jin et al., 2023).

While the presence of OCBs confirms CNS inflammation, their role in predicting long-term disease progression remains under active investigation (Stangel et al., 2013). Several studies have reported associations between CSF OCBs or elevated IgG levels and adverse radiological, cognitive, and clinical outcomes in both short- and long-term follow-ups (Akaishi et al., 2020; Farina et al., 2017). However, the prognostic value of OCB positivity, especially in terms of relapse rate and disability progression, remains debated. Some findings suggest a more aggressive disease course in OCB-positive (OCB+) patients, while others report no significant association (Avasarala et al., 2001; Liu et al., 2017; Zheng et al., 2020) .

In addition, several studies indicate that OCB positivity may increase the likelihood of conversion to secondary progressive MS (SPMS) over time. Villar et al., for example, demonstrated that patients with OCBs in CSF had significantly higher rates of disability progression and SPMS conversion (Villar et al., 2005) . Similarly, in clinically isolated syndrome (CIS), the presence of OCBs has been shown to predict future MS diagnosis and higher relapse risk (Boscá et al., 2010; Schwenkenbecher et al., 2017).

Given the ongoing uncertainty regarding the prognostic relevance of CSF OCBs and the limited data on the clinical significance of OCB subtypes, further investigation is warranted. The present study aims to assess the long-term prognostic value of OCB positivity and its subtypes (Type 2 and Type 3) in a large, well-characterised cohort of RRMS patients. Specifically, we examine the association between OCB status and key clinical outcomes, including disability progression, relapse frequency, and conversion to secondary progressive MS (SPMS) over a five-year follow-up period. By addressing this gap, the study seeks to inform the clinical utility of OCB analysis not only as a diagnostic but also as a prognostic tool in RRMS.