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  • Gary Birnbaum, MD

Scaling disability

Time between expanded disability status scale (EDSS) scores.

Zurawski J, Glanz BI, Chua A, Lokhande H, Rotstein D,

Weiner H, Engler D, Chitnis T, Healy BC.

Mult Scler Relat Disord. 2019 Feb 5;30:98-103. doi: 10.1016/j.msard.2019.02.007.


Key Points:

a) MS can affect any brain function. As a result, measuring disability in persons with MS is very difficult

b) The expanded disability status scale (EDSS), developed by Dr. John Kurtzke is the most used scale in MS clinical trials.

c) It ranges from a score of zero (normal) to ten (death). Many functions are measured, from vision, to speech, to balance, to strength, to bowel and bladder function, to coordination, and to how far a person can walk, with and without assistive devices.

d) The EDSS has several shortcomings.

e) It does not measure levels of fatigue or changes in thinking.

f) The scale is not linear. By that I mean that the changes in disability between scale numbers are not equal. For example, there are only minor differences between persons rated EDSS 1 and EDSS 2, while there are major differences between EDSS 6 (requires a single walking aid [cane, crutch] to walk about 300 feet with or without resting) and EDSS 7 (Essentially restricted to wheelchair that can be rolled independently, with ability to transfer alone).

g) This striking finding of this paper is the differences in the time intervals it took for persons with MS to move from one level of disability to another.

h) The researchers found that at the lower end of the EDSS scale time changes in disability changed relatively slowly (about 10-15 years), but as the disability progressed, movement up the scale occurred much more rapidly (~1-2 years).

i) One possibility to explain these findings is that with increasing tissue damage there is less brain reserve to compensate, so even small changes in brain function later in the disease give rise to greatly increased disability.

j) These findings have important practical implications. For example, in terms of recruiting individuals for clinical trials, should one enter persons with major disability since their disease momentum may be such that there is little chance of benefits of therapy?

k) The data also provide even more compelling evidence to initiate treatment of disease as early as possible, before disability progression has reached a “point of no return.”



The Expanded Disability Status Score (EDSS) is the most used tool to measure disability progression in persons with MS. Drugs that can show benefit in delaying progression on the EDSS are accepted by the US Food and Drug administration (FDA) as being of therapeutic value. The EDSS tries to be as inclusive as possible in evaluating most of the brain functions affected by MS. However, it has several shortcomings. It does not adequately measure such difficult to define symptoms as fatigue and cognitive functioning. In addition, as disability progresses there is increasing emphasis on ambulation, with changes in that ability alone sufficient to changing a person’s EDSS score. Finally, the scale is not linear, that is changes in disability per step are not equal. For example, moving from EDSS 1 (no disability, with minimal signs in one functional system) to EDSS 3 (moderate disability in one functional system, or mild disability in three or four functional systems) is very different than moving from EDSS 5 (disability severe enough to impair full daily activities and ability to work a full day without special provisions. Able to walk without aid or rest for ~600 feet) to EDSS 8 (confined to bed but can still communicate and eat).

The major finding in this paper how differences in degrees of disability early in the disease change, to become much more rapid as the disease progresses. Early in the disease (EDSS 0-3) progression occurs slowly, with changes in EDSS scoring taking up to 15 years in some instances. However, as disability continues, changes in EDSS parameters become much more rapid, with intervals as short as 1 to 2 years for persons with MS to moving from EDSS 5 to EDSS 6. This rapid decline in function most likely is the result of less brain reserve, or ability of the brain to compensate for increasing damage. If that is the case, persons with rapidly increasing disability may be less responsive to disease-modifying therapies. Should such individuals be kept from participating in clinical trials? In addition, at that point in their disease, the immune disturbances occurring in their central nervous systems may be very different than those present in persons with early disease, also making it less likely that they will respond to the same medications benefitting persons with early MS. Finally, the paper’s provides another strong incentive to start treatment of active disease early in its course, and thus prevent the momentum of disability to become unstoppable.


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