MS is a chronic disease presenting with progressive motor impairment, and MS patients, especially those with more severe forms of the disease, are on the whole more prone to infections . In addition, many MS patients take DMTs, which are drugs that have immunomodulatory and also immunosuppressive effects. It is these effects of DMTs that are the main reason for fears that these drugs may be responsible for a potential more severe course of COVID-19, as well as a higher mortality rate. Of particular concern are those DMTs that lead to lymphopenia and also a reduction in the B lymphocyte count, for example cladribine, alemtuzumab, ocrelizumab, and rituximab [3,4,5,6,7].
However, the prevalence of COVID-19 in MS patients based on current data appears to be similar to that in the total population [3, 4]. Furthermore, the data we know so far suggest that also DMTs do not influence the severity of COVID-19 . Nevertheless, there are some concerns—firstly, it seems reasonable to suspect that MS patients with significant motor impairment are likely to have a severe COVID-19 course and increased mortality due to their commonly poor general health . Second, alemtuzumab and cladribine have not been widely used in previous studies, and it is suspected that DMTs causing lymphopenia and reduced B lymphocyte counts may be responsible for the increased morbidity, severity, and mortality of COVID-19 [4,5,6,7]. Noteworthy, a recently presented study in a group of 844 MS patients with suspected or confirmed COVID-19 showed that anti-CD20 therapy (rituximab or ocrelizumab) was associated with a significantly increased risk of severe COVID-19 . The use of methylprednisolone in the short time before COVID-19 (less than 1 month) was further found to be a significant risk factor for severe infection .