"In a nutshell the EDSS is the flawed ‘gold standard’ we, neurologists, use to measure the impact of MS on the neurological system."
Why is the EDSS flawed?
It is not underpinned by sound scientific principles that are necessary when developing a robust and reliable outcome measure. The EDSS was developed by a neurologist, John Kurtzke, who fashioned the scale to map onto the neurological examination. As a result the EDSS has many problems. It has high variability between raters; i.e. two raters seldom get the same score when assessing the same MSer on the same day. The EDSS varies depending on the time of day the assessment is done, for example an EDSS is often lower in the morning when you are not tired compared to the afternoon when you are tired.
The EDSS has so called ceiling and floor effects; MSers move through the high and low scores very slowly, compared to the mid-range, despite obvious disease progression. In other words the EDSS is not really responsive to change and it is not a linear scale; moving from an EDSS of 2.0 to 3.0 is not the same as moving from an EDSS of 6.0 to 7.0. At lower scores (less than 5.0) the EDSS is an impairment scale; impairments are things that the neurologists detects on the neurological examination that the MSer may, or may not, be aware of. At higher scores the EDSS is a disability scale and measures the impact of MS on physical functioning and is dominated by walking or mobility. The EDSS does not measure handicap, i.e. the impact of MS on an individual’s functioning in society. Finally, the EDSS is known to be poor when it comes to capturing the impact of MS on cognition, vision, bowel, bladder and sexual dysfunction, and fatigue.
Why is the EDSS the gold standard?
Despite all its weaknesses the EDSS is not going to go away in a hurry. All the MS natural history data that has been collected in the past, and continues to be collected, is based on the EDSS. In addition, all the current DMTs have been licensed using the EDSS as the primary outcome measure. In other words the regulators, FDA (US Food and Drug Administration) and the EMA (European Medicines Agency), are comfortable with the EDSS and know it well; they are unlikely to accept a new primary outcome measure for clinical trials.
What is the problem with EDSS for MSers?
Another problem with the EDSS is that you need a neurologist to perform a neurological examination to score the EDSS. This examination has to be very detailed and takes 20-40 minutes to complete; 20-40 minutes of a neurologists time is expensive and therefore it inflates the cost of obtaining disability information and it makes clinical trials expensive to do.
The fact that the EDSS is controlled by your neurologist, and not you, gives them control over information that you need and it prevents you monitoring your own disease progression and relating it to published data on MS. In my opinion this is a problem as it disempowers you. We have addressed this by developing a web-based EDSS calculator as a proxy to the neurological EDSS. If this validates in our longitudinal studies it will allow you to calculate your own EDSS and to then use this information to monitor your own disease.
How do we calculate the EDSS?
The EDSS scale ranges from 0 to 10 in 0.5 unit increments, with one exception there is no 0.5 level. Higher scores represent higher levels of impairment or disability.
Although an EDSS of 0 (zero) is 'normal' you can still have neurological impairments detected using more sensitive tests, for example cognitive impairments.
EDSS steps 1.0 to 4.5 refer to MSer who are able to walk without an aid and is based on measures of impairment using 7 functional systems (FS):
1. Pyramidal - weakness or difficulty moving limbs.
2. Cerebellar – ataxia (unsteadiness of gait), loss of coordination or tremor.
3. Brainstem - problems with speech, swallowing, eye movements (double vision or jerky eye movements).
4. Sensory - numbness or loss of sensations.
5. Bowel, bladder and sexual function.
6. Visual function – reduction or loss of vision or a blind spot (scotoma).
7. Cerebral (or mental) functions and fatigue.
Each functional system is scored on a scale of 0 (no disability) to 5 or 6 (more severe disability)."
The following is a summary of the EDSS scores
0.0 - No disability, no abnormal clinical signs.
1.0 - No disability, minimal signs in one FS.
1.5 - No disability, minimal signs in more than one FS.
2.0 - Minimal disability in one FS.
2.5 - Mild disability in one FS or minimal disability in two FS.
3.0 - Moderate disability in one FS, or mild disability in three or four FS. No impairment to walking.
3.5 - Moderate disability in one FS and more than minimal disability in several others. No impairment to walking.
4.0 - Significant disability but self-sufficient and up and about some 12 hours a day. Able to walk without aid or rest for 500m.
4.5 - Significant disability but up and about much of the day, able to work a full day, may otherwise have some limitation of full activity or require minimal assistance. Able to walk without aid or rest for 300m.
5.0 - 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 200m.
5.5 - Disability severe enough to preclude full daily activities. Able to walk without aid or rest for 100m.
6.0 - Requires a walking aid - cane, crutch, etc - to walk about 100m with or without resting.
6.5 - Requires two walking aids - pair of canes, crutches, etc - to walk about 20m without resting.
7.0 - Unable to walk beyond approximately 5m even with aid. Essentially restricted to wheelchair; though wheels self in standard wheelchair and transfers alone. Up and about in wheelchair some 12 hours a day.
7.5 - Unable to take more than a few steps. Restricted to wheelchair and may need aid in transferring. Can wheel self but cannot carry on in standard wheelchair for a full day and may require a motorised wheelchair.
8.0 - Essentially restricted to bed or chair or pushed in wheelchair. May be out of bed itself much of the day. Retains many self-care functions. Generally has effective use of arms.
8.5 - Essentially restricted to bed much of day. Has some effective use of arms retains some self-care functions.
9.0 - Confined to bed. Can still communicate and eat.
9.5 - Confined to bed and totally dependent. Unable to communicate effectively or eat/swallow.
10.0 - Death due to MS.
"Do you know what your EDSS is? If not ask your neurologist what it is? Please be aware unless your neurologist does a detailed examination and observes you walking he/she hasn't done the EDSS properly. It should take at least 20 minutes to do an EDSS. I have timed myself doing it and I can't score the functional systems under 20 minutes. In addition the lower your EDSS score the longer it takes to do. You have to observe, and time, MSers walking to do the lower scores. The latter involves using a stopwatch and an instrument to measure walking distance. In our Department we use a measurement wheel. If your neurologist doesn't walk you he hasn't done the EDSS properly."
04 Jul 2013
Epub: Leddy S, Hadavi S, McCarren A, Giovannoni G, Dobson R. Validating a novel web-based method to capture disease progression outcomes in multiple sclerosis. J Neurol. 2013 Jun 27. Background: The Expanded ...
26 Mar 2013
Dobson R, Leddy SG, Gangadharan S, Giovannoni G. Assessing fracture risk in people with MS: a service development study comparing three fracture risk scoring systems. BMJ Open. 2013 Mar 11;3(3). doi:pii: e002508.