The Expanded Disability Status Scale (EDSS), the primary tool used to measure MS disability, was developed in 1983 to assess walking ability. We now know that MS affects far more than mobility. Fatigue affects 94 percent of people with MS, while 75 percent report cognitive difficulties, but both are absent in the EDSS assessment.3 In a field where clinical consensus is rare, seven in ten neurologists agree: a more comprehensive approach is needed.3
Growing recognition of smouldering neuroinflammation has made the need for new methods of quantifying MS progression increasingly urgent. This slow, chronic disease activity can persist even when a patient appears clinically stable, with effects that are subtle, cumulative and easy to miss until significant damage has already occurred.4
This is why Sanofi initiated the development of the Smouldering Associated Worsening (SAW) Index+. The SAW Index Study — led by an international steering committee of leading MS clinicians, researchers and patient advocates — is due to complete in 2027. Based on hundreds of hours of in-depth qualitative research with people with MS, the goal of the SAW Index is to provide neurologists with a comprehensive measurement framework that bridges the gap between lived experience and what clinical tools are currently able to detect.
According to the European Multiple Sclerosis Platform, people with MS experience an average of 14 symptoms within the first five years of diagnosis, with fatigue, sensory problems, sleep disturbances, cognitive impairment and balance problems among the most common.5 These are precisely the experiences the SAW Index is designed to surface, replacing static labels like “moderately affected” with measurement metrics grounded in the experience and words of people with MS.
The cost of this gap
These aspects of MS can be challenging to quantify and are associated with substantial societal and economic burdens. Lifetime productivity loss per person with MS ranges from €394,000 in France to €668,000 in Germany.3 The cost profile shifts significantly as the disease progresses: in mild MS, direct healthcare costs dominate; in severe MS, indirect costs become the primary driver.3 Indeed, lost wages, absenteeism, early retirement, disability payments and the growing burden on unpaid carers outweigh medical costs in many countries, placing growing long-term pressure on social insurance and disability systems.3