Multiple Sclerosis (MS) is a chronic, autoimmune and heterogeneous disease of the central nervous system (CNS) (Filippi et al., 2018). Since 1990, there has been a 10.4 % increase in the global prevalence of MS, as reported in 2016 by the Global Burden of Disease collaborator group (Wallin et al., 2019). Approximately 2.2 million cases of MS have been reported worldwide. Local researchers have reported varying prevalence ratios (23.8–48.3/105 (Cristiano et al., 2020; Luetic and Menichini, 2021; Mellinger et al., 2018)) in different regions of Argentina. A 22-year study in Buenos Aires reported an increasing incidence of MS in women (from 1/105 to 4.9/105) between 1992 and 2013 (Cristiano et al., 2016).

MS disease indicator is the buildup of regions of demyelination in the CNS but the development of this disease is diverse (Filippi et al., 2018) with several distinct clinical phenotypes (Lassmann et al., 2012). Approximately 85 % of patients are diagnosed with relapsing-remitting MS [RRMS] (Klineova and Lublin, 2018), a phase of MS characterized by episodes of neurological deficits called “relapses”, with full or partial recovery. Over time, clinical disability and its progression might become permanent, which is a characteristic of the secondary progressive phase of MS (SPMS) (Filippi et al., 2018). The probability of progressing into the SPMS phase increases proportionally with disease duration, with a 2-fold increase per decade, and approximately 50 %–60 % of patients with RRMS develop SPMS within 15–20 years of the onset of RRMS (Giovannoni et al., 2016; Scalfari et al., 2014). There is no distinct demarcation between the two phases of MS (leading to a delay in SPMS diagnosis) and DMTs cannot prevent the transition from RRMS to SPMS (Gajofatto and Benedetti, 2015; Lublin and Reingold, 1996; Oh et al., 2019; Scalfari et al., 2014). As disability progresses since the early stage of the disease, the neurologist may miss the best therapeutic window to treat MS with disease-modifying therapies (DMTs) (Alkhawajah and Oger, 2011; Jones and Coles, 2010; Lublin et al., 2022; Scalfari et al., 2013).

As there are no clear clinical, immunological, pathological or imaging-based criteria to determine the transition from RRMS to SPMS (Katz Sand et al., 2014), neurologists usually wait till the accumulation of considerable disability and the cessation of episodic disease activity before confirming a diagnosis of SPMS (Lorscheider et al., 2016). Besides, physicians may be hesitant to diagnose SPMS due to the associated psychological burden (Davies et al., 2016; O'Loughlin et al., 2017). The diagnosis of SPMS is usually retrospective, mostly based on the history of worsening after the initial relapsing disease course (Lublin et al., 2014; Oh et al., 2019), and has often been delayed in clinical practice (Katz Sand et al., 2014). In Argentina, a diagnostic uncertainty period of 3.3 years regarding the transition from RRMS to SPMS has been recently reported by Rojas et al. (Rojas et al., 2021). Due to this diagnostic uncertainty, neurologists have to look for objective measures of progression to detect transition from RRMS to SPMS over time. MSProDiscuss™, was a physician-completed digital tool based on a set of weighted questions that include information on patient relapses, symptoms and impacts experienced within the past 6 months (Ziemssen et al., 2020). This tool has been developed a couple of years ago and validated by experienced MS neurologists, patients, and empirical assessments of real-world evidence. A traffic-light system within the MSProDiscuss™ tool facilitates the discussion on the risk of disability progression from RRMS to SPMS.

As MS is a chronic disease that progresses through the years and most clinical trials have a short follow-up duration, it is difficult to assess disability and DMTs effectiveness in the long term (Goodin et al., 2002). Thus, collection of real-world data after several years of disease can clarify the status of those patients, supporting clinical practice and ensuring those long-term patients can receive the appropriate treatment. To this end, we conducted a cross-sectional study in Argentina to determine the level of disability in patients with ≥10 years of disease duration since the first diagnosis of MS. In addition, the risk of disability progression, the distribution of diagnoses between RRMS and SPMS, patient demographics, and disease history have been evaluated.