The Expanded Disability Status Scale (EDSS)

    The EDSS is a classification scheme (Rating Scale) that insures all participants in a clinical trial are in the same class, type, or phase of MS.

    It is also used by Neurologists to follow the progression of Multiple Sclerosis disability and evaluate treatment results, for similar groupings of people. The Functional System (FS) scale is incorporated within its overall framework.

The Expanded Disability Status Scale (EDSS)

0.0 - Normal Neurological Exam.
1.0 - No disability, minimal signs on 1 FS.
1.5 - No disability minimal signs on 2 of 7 FSs.
2.0 - Minimal disability in 1 of 7 FSs.
2.5 - Minimal disability in 2 FSs.
3.0 - Moderate disability in 1 FS; or mild disability in 3 - 4 FSs, though fully ambulatory.
3.5 - Fully ambulatory but with moderate disability in 1 FS and mild disability in 1 or 2 FS; or moderate disability in 2 FS; or mild disability in 5 FSs.
4.0 - Fully ambulatory without aid, up and about 12hrs a day despite relatively severe disability. Able to walk without aid 500 meters.
4.5 - Fully ambulatory without aid, up and about much of day, able to work a full day, may otherwise have some limitations of full activity or require minimal assistance. Relatively severe disability. Able to walk without aid 300 meters.
5.0 - Ambulatory without aid for about 200 meters. Disability impairs full daily activities.
5.5 - Ambulatory for 100 meters, disability precludes full daily activities.
6.0 - Intermittent or unilateral constant assistance (cane, crutch or brace) required to walk 100 meters with or without resting.
6.5 - Constant bilateral support (cane, crutch or braces) required to walk 20 meters without resting.
7.0 - Unable to walk beyond 5 meters even with aid, essentially restricted to wheelchair, wheels self, transfers alone; active in wheelchair about 12 hours a day.
7.5 - Unable to take more than a few steps, restricted to wheelchair, may need aid to transfer; wheels self, but may require motorized chair for full day's activities.
8.0 - Essentially restricted to bed, chair, or wheelchair, but may be out of bed much of day; retains self care functions, generally effective use of arms.
8.5 - Essentially restricted to bed much of day, some effective use of arms, retains some self care functions.
9.0 - Helpless bed patient, can communicate and eat.
9.5 - Unable to communicate effectively or eat/swallow.
10.0 - Death.

The EDSS has several well-recognized shortcomings. Because of its strong emphasis on ambulation in the middle range of the scale, the EDSS is insensitive to changes in other Neurological functions, in patients with moderate to severe disability.

Like all rating scales based on the standard Neurological Examination, the EDSS is insensitive to Cognitive dysfunction in MS.

The definitions of how to rate findings on the Neurological Examination, how these findings translate into the Functional System Status scores, and the rules governing how the EDSS is calculated are somewhat complicated.

These ambiguities contribute to the significant intra-rater and inter-rater variability observed in several studies.

Variability in the EDSS can be reduced but not eliminated by development of explicit instructions and formal training of raters. Lastly, the EDSS is an Ordinal (nonlinear discontinuous) scale.

That is, the meaning of a 1.0-step change varies in different parts of the scale. This property has two consequences.

  1. Studies of large populations of MS patients have revealed consistently a bimodal EDSS frequency distribution rather than a Gaussian distribution, with a paucity of patients in the 4.0 to 5.5 EDSS range.

  2. The duration of time individual patients spend at the EDSS steps during the course of their disease varies over the range of the EDSS.
    • For example, the average duration at EDSS 4.0 is 1.22 years, compared with 3.77 years at EDSS 7.0.

All of these properties make the EDSS relatively insensitive to change, as patients deteriorate over time.

Other rating scales based on the standard Neurological Examination share many of these shortcomings.

Also See:
Kurtzke Scales Revisited:
The Application Of Psychometric Methods To Clinical Intuition

by: Jeremy Hobart, Jenny Freeman and Alan Thompson
Brain, Vol. 123, No. 5, 1027-1040, May 2000

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