The Expanded Disability Status Scale (EDSS)
Understanding the role of the EDSS to evaluate MS in patients.
The Expanded Disability Status Scale (EDSS) is the most commonly used rating scale to evaluate the clinical status of patients with MS. It measures disability along several separate parameters: strength, sensation, brainstem functions (speech and swallowing), coordination, vision, cognition, and bowel/bladder continence. It has the advantage of being a well-accepted measure of disability in MS and it is not particularly difficult or time consuming to perform.
The EDSS is a 10-point scale that can essentially be divided into three sections:
- Scores 1-4: Patients unrestricted in their walking, but may have significant disability in other areas.
- Scores 4-7: Patients are unable to walk without the use of assistive devices
- Scores 7-10: Patients are bed-bound and may require near-total care.
Despite its advantages, there are many well-recognized problems with this scale. The first of these is that it is heavily dependent on the ability to walk and therefore may fail to represent patients with significant disabilities in other domains. Although patients are given a score in all of the 6 domains listed above, they are not all weighted equally. I have some patients who are able to walk relatively well, yet have severe impairment in another domain that is not well-represented in the EDSS. These include patients with significant visual impairment, significant pain, severely impaired cognition/psychiatric symptoms, and incontinence. Since these patients do not have significant gait impairment, however, their EDSS score will remain low, giving the false appearance that they do not suffer from significant disability. Moreover, the same disability can affect different people in different ways. One patient of mine is a construction worker who had to give up his job due to leg weakness, while another patient is a lawyer who continued to work for many years with the same level of disability.
A second disadvantage of the scale is that it is non-linear. Simply put, this means that a patient who has increase in their EDSS from 1 to 2 may only have a slight increase in their symptoms. In contrast, an increase from a 5 to 6 may mean the difference between being able to work or not, or living independently or not. Each of these cases would be deemed as having a 1-point increase in the EDSS, with no regard for the practical impact on a patient’s life.
The EDSS score needs to be interpreted over the course of a patient’s illness. While most patients tend to slowly accumulate disability in MS, many can remain stable for years or decades. So, a 60 year-old patient who has had an EDSS score of 4, might actually be doing very well, if his score has not changed in many years. In contrast, a score of 4 would be of great concern in a younger person who had a lower score only a few years prior.
Finally, while the EDSS in invaluable for clinical studies, it is difficult to use the EDSS score to make a treatment decision for any individual patient. I think most neurologists prefer not to use a number to make a decision about how to treat their patients. So many of the symptoms of MS are subjective and our patients lead such varying lives that their illness is very difficult to capture in a single score. While the EDSS will remain an invaluable tool for clinical trials, it does not remain a substitute for talking to and examining each patient as an individual.
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