The Expanded Disability Status Scale (EDSS) is a method of quantifying disability in multiple sclerosis and monitoring changes in the level of disability over time. It is widely used in clinical trials and in the assessment of people with MS.
The scale was developed by a neurologist called John Kurtzke in 1983 as an advance from his previous 10 step Disability Status Scale (DSS).
The EDSS scale ranges from 0 to 10 in 0.5 unit increments that represent higher levels of disability. Scoring is based on an examination by a neurologist.
EDSS steps 1.0 to 4.5 refer to people with MS who are able to walk without any aid and is based on measures of impairment in eight functional systems (FS):
- pyramidal – muscle weakness or difficulty moving limbs
- cerebellar – ataxia, loss of balance, coordination or tremor
- brainstem – problems with speech, swallowing and nystagmus
- sensory – numbness or loss of sensations
- bowel and bladder function
- visual function - problems with sight
- cerebral functions - problems with thinking and memory
A functional system (FS) represents a network of neurons in the brain with responsibility for particular tasks. Each FS is scored on a scale of 0 (no disability) to 5 or 6 (more severe disability).
EDSS steps 5.0 to 9.5 are defined by the impairment to walking. The scale is sometimes criticised for its reliance on walking as the main measure of disability.
Although the scale takes account of the disability associated with advanced MS, most people will never reach these scores. A large study that looked at people with MS at a clinic in Ontario (prior to the development of the expanded version) found that 51% of people had a DSS score of 5 or lower. 88% had a score of 7 or lower.