Multiple sclerosis (MS) is an unpredictable, often disabling disease of the central nervous system that disrupts the flow of information within the brain, and between the brain and body.
The cause of MS is still unknown – scientists believe the disease is triggered by as-yet-unidentified environmental factor in a person who is genetically predisposed to respond. The progress, severity and specific symptoms of MS in any one person cannot yet be predicted. Most people with MS are diagnosed between the ages of 20 and 50, with at least two to three times more women than men being diagnosed with the disease.
There are 4 main types of MS –
- RRMS – the most common disease course – is characterized by clearly defined attacks of new or increasing neurologic symptoms. These attacks – also called relapses or exacerbations – are followed by periods of partial or complete recovery (remissions). During remissions, all symptoms may disappear, or some symptoms may continue and become permanent. However, there is no apparent progression of the disease during the periods of remission. At different points in time, RRMS can be further characterized as either active (with relapses and/or evidence of new MRI activity) or not active, as well as worsening (a confirmed increase in disability over a specified period of time following a relapse) or not worsening. Approximately 85% of people with MS are initially diagnosed with RRMS.
- PPMS is characterized by worsening neurologic function (accumulation of disability) from the onset of symptoms, without early relapses or remissions. PPMS can be further characterized at different points in time as either active (with an occasional relapse and/or evidence of new MRI activity) or not active, as well as with progression (evidence of disease worsening on an objective measure of change over time, with or without relapse or new MRI activity) or without progression. Approximately 15% of people with MS are diagnosed with PPMS.
- SPMS follows an initial relapsing-remitting course. Most people who are diagnosed with RRMS will eventually transition to a secondary progressive course in which there is a progressive worsening of neurologic function (accumulation of disability) over time. SPMS can be further characterized at different points in time as either active (with relapses and/or evidence of new MRI activity) or not active, as well as with progression (evidence of disease worsening on an objective measure of change over time, with or without relapses) or without progression.
- CIS is a first episode of neurologic symptoms caused by inflammation and demyelination in the central nervous system. The episode, which by definition must last for at least 24 hours, is characteristic of multiple sclerosis but does not yet meet the criteria for a diagnosis of MS because people who experience a CIS may or may not go on to develop MS.
Multiple sclerosis is thought to affect more than 2.3 million people worldwide. While the disease is not contagious or directly inherited, epidemiologists — scientists who study patterns of disease — have identified factors in the distribution of MS around the world that may eventually help determine what causes the disease. These factors include gender, genetics, age, geography and ethnic background.
Epidemiology is the branch of medicine that deals with the incidence, distribution, and possible control of diseases and other factors relating to health. Epidemiological studies are challenging for several reasons:
- MS can be difficult to diagnose. Since there is no single test for MS, the diagnosis can be missed, delayed or even incorrect.
- MS is not a “reportable” disease, which means that the government does not require physicians to inform any central database when they make the diagnosis. Without this kind of centralized reporting system, there is no easy way to count people with MS.
- Data from earlier epidemiological studies may not accurately represent the current MS population because the investigators used different methods for identifying and counting people with MS, as well as different strategies for analyzing their data.
For more information, visit the National MS Society at http://www.nationalmssociety.org.