Infection Risk in Patients on Multiple Sclerosis Therapeutics

The interface of multiple sclerosis (MS) and infection occurs on several levels. First, infectious disease has been postulated as a potential trigger, if not cause, of MS. Second, exacerbation of MS has been well-documented as a consequence of infection, and, lastly, infectious diseases have been recognized as a complication of the therapies currently employed in the treatment of MS. MS is a disease in which immune dysregulation is a key component. Examination of central nervous system (CNS) tissue of people affected by MS demonstrates immune cell infiltration, activation and inflammation. Therapies that alter the immune response have demonstrated efficacy in reducing relapse rates and evidence of brain inflammation on magnetic resonance imaging (MRI). Despite the altered immune response in MS, there is a lack of evidence that these patients are at increased risk of infectious disease in the absence of treatment or debility. Links between infections and disease-modifying therapies (DMTs) used in MS will be discussed in this review, as well as estimates of occurrence and ways to potentially minimize these risks. We address infection in MS in a comprehensive fashion, including (1) the impact of infections on relapse rates in patients with MS; (2) a review of available infection data from pivotal trials and postmarketing studies for the approved and experimental DMTs, including frequency, types and severity of infections; and (3) relevant risk minimization strategies, particularly as they pertain to progressive multifocal leukoencephalopathy (PML).