OCBs are clonally restricted immunoglobulins G (IgG) produced by activated plasma cells within the central nervous system (CNS), and their presence in the CSF is considered a hallmark of an ongoing inflammatory process in the CNS (Winger and Zamvil, 2016; Deisenhammer et al., 2019; Dobson et al., 2013; Pryce and Baker, 2018; Obermeier et al., 2011). OCBs are commonly found in MS, occurring in 85 %−95 % of patients (Deisenhammer et al., 2019; Dobson et al., 2013; ), (Pryce and Baker, 2018; Wu et al., 2010; Matute-Blanch et al., 2018; Freedman et al., 2005; Bourahoui et al., 2004), and various reviews and meta-analyses over the years have demonstrated high specificity and positive predictive value (PPV) of OCBs for MS (Deisenhammer et al., 2019; Pryce and Baker, 2018; Tintoré et al., 2001; Petzold, 2013).

In addition to being highly sensitive, the presence of OCBs in patients with clinically isolated syndrome (CIS) doubles the risk of conversion to MS (Dobson et al., 2013; Tintoré et al., 2001; Tintore et al., 2008; Andreadou et al., 2013; Kuhle et al., 2015; Tintore et al., 2015; Huss et al., 2016; Martinelli et al., 2017). Moreover, the presence of OCBs in MS is associated with a more aggressive course (Dobson et al., 2013; Lechner-Scott et al., 2012; Joseph et al., 2009; Siritho and Freedman, 2009; Annunziata et al., May 2006; Rojas et al., 2012; Farina et al., 2017). Recently, OCBs presence in the CSF was determined to be equivocal to dissemination in time (DIT), facilitating earlier diagnosis of definite MS in patients with one clinical attack who fulfil the criteria for dissemination in space (DIS) (Arrambide et al., 2018; Thompson et al., 2018).

MS attacks may be treated acutely with a short course of high dose IVMP, which hastens recovery and reduces the risk of disability caused by the attack (Compston, 1988; Kupersmith et al., 1994; Tremlett et al., 1998; Brusaferri and Candelise, 2000; Beck et al., 1992). Previous studies reported that high dose corticosteroids can decrease OCBs count and IgG index in the CSF if started just before LP (Massaro, 1978; Frequin et al., 1992; Trotter and Gamey, 1980). Considering the importance of OCBs in the diagnosis and prognosis of MS it is vital to determine whether LP performed after initiation of IVMP influences the OCBs result.

The aim of our study was to examine whether IVMP initiation prior to CSF collection affects OCBs results in patients presenting with acute demyelinating attack. Additionally, we examined whether other clinical characteristics are associated with the presence of OCBs in the CSF.