The Kurtzke Expanded Disability Status Scale (EDSS) is a method of quantifying disability in multiple sclerosis. The scale has been developed by John F. Kurtzke. The EDSS is based on a neurological examination by a clinician. However, a number of versions have been developed which enable patient self-administration. The EDSS quantifies disability in eight Functional Systems (FS) by assigning a Functional System Score (FSS) in each of these functional systems. It consists of ordinal rating system ranging from 0 (normal neurological status) to 10 (death due to MS) in 0.5 increments interval (when reaching EDSS 1). The lower scale values of the EDSS measure impairments based on the neurological examination, while the upper range of the scale (> EDSS 6) measures handicaps of patients with MS. The determination of EDSS 4 – 6 is heavily dependent on aspects of walking ability. The EDSS is the most widely used measurement tool to describe disease progression in patients with MS and to assess the effectiveness of therapeutic interventions in clinical trials. Nonetheless, it has many criticisms, including the fact that it has moderate intra-rater reliability (EDSS kappa values between 0.32 and 0.76 and between 0.23 and 0.58 for the individual FSs were reported), offers poor assessment of upper limb and cognitive function, and lacks linearity between score difference and clinical severity. Other limitations of EDSS include that it relies heavily on the evaluation of motor function and the ability to walk; as such, a patient who might not be able to walk but maintains full dexterity is classified toward the severe end of the scale. Other validated assessment measures used in MS trials include the Timed 25-Foot Walk, the Multiple Sclerosis Functional Composite, and the Short Form (36) Health Survey.

Functional systems

Kurtzke defines functional systems as follows:

Results and clinical meaning

EDSS steps 1.0 to 4.5 refer to people with MS who are fully ambulatory. EDSS steps 5.0 to 9.5 are defined by the impairment to ambulation. The clinical meaning of each possible result is the following: