'No evidence of disease activity' - is it an appropriate surrogate in multiple sclerosis?

The increasing number of disease-modifying treatments available for multiple sclerosis has broadened treatment options for patients, but also challenges clinicians to select the best therapy for each individual at the appropriate stage of the disease. Early prediction of treatment response still remains one of the main difficulties in the management of multiple sclerosis patients. The concept of 'no evidence of disease activity' (NEDA) has been proposed as a surrogate for treatment response based on the absence of relapses, disability progression and radiological activity. Although there are several apparently logical arguments for the NEDA approach, there are also some major concerns that have to be considered and that are not sufficiently addressed yet. Amongst others, each parameter's limitations are not eliminated solely by its use within a composite score, and the contribution of each parameter to NEDA is not well balanced, as the detection of, for example, a single new magnetic resonance imaging lesion is considered as significant as the occurrence of a severely disabling relapse. NEDA in its current form also neglects underlying pathophysiology of the disease, has not been shown to fulfil formal criteria of a surrogate marker and its prognostic value has not been sufficiently evidenced yet. From a clinical point of view, 'evidence of disease activity' seems the more relevant surrogate; however, its implications are even less clear than those of NEDA. Here, existing literature on NEDA is critically reviewed and improvements are discussed that value its potential use in clinical trials and, even more importantly, treatment decision making in daily routine.