Apparent changes in the epidemiology and severity of multiple sclerosis

Multiple sclerosis (MS) is an immunological disease that causes acute inflammatory lesions and chronic inflammation in the CNS, leading to tissue damage and disability. As awareness of MS has increased and options for therapy have come into use, a large amount of epidemiological data have been collected, enabling studies of changes in incidence and disease course over time. Overall, these data seem to indicate that the incidence of MS has increased, but the course of the disease has become milder, particularly in the 25 years since the first disease-modifying therapies (DMTs) became available. A clear understanding of these trends and the reasons for them is important for understanding the factors that influence the development and progression of MS, and for clinical management with respect to prevention and treatment decisions. In this Review, we consider the evidence for changes in the epidemiology of MS, focusing on trends in the incidence of the disease over time and trends in the disease severity. In addition, we discuss the factors influencing these trends, including refinement of diagnostic criteria and improvements in health-care systems that have increased diagnosis in people with mild disease, and the introduction and improvement of DMT. In this Review, Koch-Henriksen and Magyari consider the evidence for changes in the epidemiology of multiple sclerosis, focusing on trends in the incidence of the disease over time and trends in the disease severity, and discuss the factors influencing these trends. Key points Most studies of multiple sclerosis (MS) in the same population over time have shown that the incidence has increased. At least a part of the increase in incidence can be attributed to improved public awareness, better health care, more MS specialists and MRI scanners, and changing diagnostic criteria. In parallel with the increase in incidence, the disease course of MS has also changed; time to disability has lengthened and survival has improved in patients with relapsing–remitting MS. Changes in disease course are likely to have resulted from more complete diagnosis of benign MS, disease-modifying therapies and lifestyle-driven changes in the natural history of the disease. Understanding the reasons for the changing epidemiology of MS is important and provides insight into factors that influence development and progression of MS and for clinical management.