Expanded Disability Status Scale & Kurtzke Functional Systems Score

Last Updated

April 04, 2018

Purpose

The FSS and EDSS are two complementary assessments that evaluate neurological impairments as a result of Multiple Sclerosis (Kurtzke, 1983). Together they aim to identify the level of impairment an individual with MS is experiencing at the time of assessment (Kurtzke, 1983). The assessment was created to inform intervention planning by quantifying the severity of impairments due to MS (Hobart, Freeman, & Thompson, 2000).

Acronym EDSS & FSS

Area of Assessment

Coordination
Gait
Mental Health
Vision & Perception

Assessment Type

Performance Measure

Administration Mode

Paper & Pencil

Cost

Free

Multiple Sclerosis

The EDSS was first reported by Kurtke in 1983 and is based on the FSS, originally developed as the Disability Status Scale (DSS) in 1955. The DSS was subsequently modified to the FSS. The EDSS/FSS is completed by a physician (usually a neurologist) and is considered to be the gold standard measure for individuals with MS. A computer system has been developed to compute EDSS scores semi-automatically, but does not appear to be commonly discussed in the literature. A calculator version, for use by personal digital assistants and computer, is also available and may be downloaded/purchased through iTunes and Android, among others.
The EDSS is scored on a 1 – 10 scale (1 = normal neurological exam to 10 – death due to MS). The FSS is based on 8 functional central venous system (FS) components: pyramidal, cerebellar, brainstem, sensory, bowel/bladder, visual, cerebral and other. Each of these systems is independent from the others, but collectively they represent all neurological impairment seen in MS. Each of these 8 items is scored on an ordinal clinical rating scale from 0-5 or 0-6 and requires client participation.
The EDSS and FSS assessments are intended to be used in conjunction with one another. The FSS should first be administered by the evaluator and results from this assessment are then applied to determine an EDSS scale score (Kurtzke, 1983). A change in the EDSS should only occur if there has been a change of one or more in the FS scores (Hobart et al., 2000)
FSS
● 7 neurological functioning systems evaluated
● 4 systems graded on a 6-point scale and 3 systems graded on a 5-point scale.
● Scores range from 0 (“normal”) to 5 or 6 (complete loss of function in the particular neurological system)
● Neurologist administers a neurological assessment and completes the FSS form based on his or her clinical observations
EDSS
● 1 grading scale
● Minimum score of 0 and maximum score of 10
● Scores range from 0 (“normal neurological exam”) to 10 (“Death due to MS”) with midrange scores including various levels of disability based on FS scores and ambulatory abilities
● Neurologist administers a neurological assessment and completes the form based on his or her clinical observations in combination with scores from FSS.

Number of Items

EDSS and FSS forms
pen/pencil

15-30 minutes

Required Training

No Training

18 +

years

Instrument Reviewers

Initially reviewed by Kirsten Potter, PT, DPT, MS, NCS and Kathleen Brandfass, MS, PT and the MS EDGE task force of the neurology section of the APTA in 2011; updated by University of Illinois at Chicago Master of Science in Occupational Therapy students Lauren Duffy, Allison Rosen, and Caroline Stevens in 2018.

Body Part

Head
Neck
Upper Extremity
Back
Lower Extremity

ICF Domain

Body Structure
Body Function
Activity

Measurement Domain

Activities of Daily Living
Motor
Sensory

Professional Association Recommendation

Recommendations for use of the instrument from the Neurology Section of the American Physical Therapy Association’s Multiple Sclerosis Taskforce (MSEDGE), Parkinson’s Taskforce (PD EDGE), Spinal Cord Injury Taskforce (PD EDGE), Stroke Taskforce (StrokEDGE), Traumatic Brain Injury Taskforce (TBI EDGE), and Vestibular Taskforce (VEDGE) are listed below. These recommendations were developed by a panel of research and clinical experts using a modified Delphi process.

For detailed information about how recommendations were made, please visit: http://www.neuropt.org/go/healthcare-professionals/neurology-section-outcome-measures-recommendations

Abbreviations:
HR	Highly Recommend
R	Recommend
*LS / UR*	Reasonable to use, but limited study in target group / Unable to Recommend
NR	Not Recommended

Recommendations for use based on acuity level of the patient:

Acute

(CVA < 2 months post)

(SCI < 1 month post)

(Vestibular < 6 months post)

Subacute

(CVA 2 to 6 months)

(SCI 3 to 6 months)

Chronic

(> 6 months)

StrokEDGE

Recommendations based on level of care in which the assessment is taken:

Acute Care

Inpatient Rehabilitation

Skilled Nursing Facility

Outpatient

Rehabilitation

Home Health

StrokEDGE

TBI EDGE

Recommendations for use based on ambulatory status after brain injury:

	Completely Independent	Mildly dependant	Moderately Dependant	Severely Dependant
TBI EDGE	N/A	N/A	N/A	N/A

Recommendations for entry-level physical therapy education and use in research:

	Students should learn to administer this tool? (Y/N)	Students should be exposed to tool? (Y/N)	Appropriate for use in intervention research studies? (Y/N)	Is additional research warranted for this tool (Y/N)
StrokEDGE	No	Yes	Yes	Not reported
TBI EDGE	No	Yes	Yes	Not reported

Many practitioners and researchers are dissatisfied with the strength of the psychometric properties of the FSS and EDSS. This has led to the creation of other measures, but they are not widely accepted or used like the FSS and EDSS (National Multiple Sclerosis Society, 2018).

It is essential that the rater uses their clinical judgment when assessing the patient. A strong understanding of neurology is required to accurately complete the evaluation (National Multiple Sclerosis Society, 2018).

Considerations

It is important to note that scores on both the FSS and EDSS are ordinal, rather than nominal, suggesting that the differences between each score are not linear (National Multiple Sclerosis Society, 2018). Kurtzke’s assumptions regarding the progression of Multiple Sclerosis have not been tested (Hobart et al., 2000). The lower scores of the EDSS are based on neurological changes detected from the physician’s exam, whereas the high scores are rooted in the impact of the illness on disability (Meyer-Moock, Feng, Maeurer, Dippel, & Kohlmann, 2014).

The FSS and EDSS are the most commonly used evaluations for assessing the effects of MS on an individual, and they are anticipated to remain widely used tools in both clinical assessment and research. However, it is recognized that the assessments have many shortcomings due to their weaker than desirable psychometric properties (National Multiple Sclerosis Society, 2018). The EDSS and FSS are currently the only evaluations of disability for Multiple Sclerosis that comprehensively cover all causes of disability through looking at the seven neurological domains (Holol, Orav, & Weiner, 1999).

Strong knowledge of neurological systems is required for the individual administering the assessments. It is strongly advised that the physician administer each of the assessments.

Standard Error of Measurement (SEM)

Multiple Sclerosis: (Hobart, Freeman, & Thompson, 2000; inter-rater reproducibility of EDSS n = 125; mean age = 43.8 (11.6) years; female = 64%; relapse-remitting MS = 7.2%; progressive MS = 92.8%)

SEM = 0.47

Multiple Sclerosis: (Hobart et al., 2000; inter-rater reproducibility of FS n = 125; mean age = 43.8 (11.6) years; female = 64%; relapse-remitting MS = 7.2%; progressive MS = 92.8%)

SEM for each functional system:
- Pyramidal SEM = 0.52
- Cerebellar SEM = 0.99
- Brainstem SEM = 0.56
- Visual SEM = 1.02
- Bladder and Bowels SEM = 0.78
- Sensory SEM = 1.29
- Mental SEM = 0.76

Multiple Sclerosis: (Hobart et al., 2000; intra-rater reproducibility of EDSS n = 40; mean age = 45.8 (11.4) years; female = 72.5%; relapse-remitting MS = 10%; progressive MS= 90%)

SEM rater 1 = 0.24
SEM rater 2 = 0.62

Multiple Sclerosis: (Hobart et al., 2000; intra- rater reproducibility of FS; n = 40; mean age = 45.8 (11.4) years; % female= 72.5%; % relapse-remitting MS = 10%; % progressive MS = 90%)

SEM for each functional system with rater 1:
- Pyramidal SEM = 0.46
- Cerebellar SEM = 0.52
- Brainstem SEM = 0.37
- Visual SEM = 0.86
- Bladder and Bowels SEM = 0.81
- Sensory SEM = 0.77
- Mental SEM = 0.87
SEM for each functional system with rater 2:
- Pyramidal SEM = 0.45
- Cerebellar SEM =0.63
- Brainstem SEM = 0.59
- Visual SEM = 0.71
- Bladder and Bowels SEM = 1.00
- Sensory SEM = 0.66
- Mental SEM = 0.61

Minimal Detectable Change (MDC)

Due to the SEM breakdown above, no MDC can be calculated for overall assessments.

Interrater/Intrarater Reliability

Multiple Sclerosis: (Meyer-Moock, Feng, Mauerer, Dippel, & Kohlmann, 2014; systematic review)

Poor to Excellent inter-rater reliability for EDSS: (Kappa = .32-.76)
Poor to Adequate inter-rater reliability for FSS: (Kappa = .23-.58)
Intra-rater not specified but reported as more variable for lower EDSS Scores than higher EDSS scores

Multiple Sclerosis: (Sharrack, Hughes, Soudain, & Dunn, 1999)

Inter-rater Reliability (n = 64; median age = 40 years; age range = 22-74; median disease duration = 13 years)
- Adequate inter-rater reliability for EDSS scores (kappa coefficient = 0.65)
- Excellent Inter-rater reliability for EDSS scores (ICC = 0.99)
- Adequate inter-rater reliability for FS scores (kappa coefficient = 0.41-0.67)
- Excellent inter-rater reliability for FS scores (ICC = 0.81-0.95)
Intra-rater Reliability (n = 35; median age = 38 years; age range = 24-51; median disease duration = 11 years)
- Adequate intra-rater agreement on FS scores (kappa coefficient = 0.42-0.66)
- Adequate to Excellent intra-rater agreement on FS scores (ICC = 0.67-0.92)
- Adequate intra-rater reliability on EDSS scores (kappa coefficient = 0.7)
- Excellent intra-rater reliability on EDSS scores (ICC = 0.99)

Multiple Sclerosis: (Hobart et al., 2000)

Inter-rater reliability of EDSS n = 125; mean age = 43.8 (11.6) years; % female = 64%; % Relapse-remitting MS = 7.2%; % progressive MS = 92.8%
- Excellent (ICC = 0.78)
Inter-rater reproducibility of FS scores n = 125; mean age = 43.8 (11.6) years; % female = 64%; % Relapse-remitting MS = 7.2%; % progressive MS = 92.8%
- Poor to Adequate (ICC = 0.38-0.72)
Intra-rater reproducibility of EDSS n = 40; mean age = 45.8 (11.4) years; % female = 72.5%; % Relapse-remitting MS = 10%; % progressive MS = 90%
- Adequate to Excellent (ICC = 0.61-0.94)
Intra-rater reproducibility of FS scores n = 40; mean age = 45.8 (11.4) years; % female = 72.5%; % Relapse-remitting MS = 10%; % progressive MS = 90%
- Poor to Excellent (ICC = 0.28-0.79) for rater 1 across the functional systems
- Adequate to Excellent (ICC = 0.67-0.83) for rater 2 across the functional systems

Construct Validity

Convergent and Discriminant Validity:

Multiple Sclerosis: (Sharrack et al., 1999; n = 50)

Excellent validity when correlating EDSS scores with The Barthel Index (r = -0.74)
Excellent validity when correlating EDSS score with London Handicap Scale (r = -0.69)
Excellent validity when correlating EDSS score on the physical functioning item of the SF-36 (r = -0.82)
Adequate, statistically significant, validity when correlating EDSS scores with physical role limitation item of SF-36 (r = -0.50)
Poor, but statistically significant, validity when correlating EDSS scores with general health perception item of SF-36
Poor, but statistically significant, validity when correlating EDSS scores with social functioning item of SF-36 (r = -0.47)

Multiple Sclerosis: (Meyer-Moock et al., 2014)

Adequate to Excellent validity established against the Barthel Index (no specific data reported)
Adequate to Excellent validity established against the London Handicap Scale (no specific data reported)
Adequate to Excellent validity established against the Scripps Neurological Rating Scale (no specific data reported)
Adequate to Excellent validity established against the Functional Independence Measure (no specific data reported)
Adequate to Excellent alidity established against the SF-36 Physical Function Ability (no specific data reported)
Poor validity established against the Ambulation Index
Poor validity established against an MRI-measured neuropsychological impairment and brain changes
Poor correlation with patient reported outcomes

Multiple Sclerosis: (Hobart et al., 2000) n = 64

Correlates highly with Barthel Index (BI) and Functional Independence Measure (FIM)
- Excellent product-moment correlation with BI = -0.89
- Excellent product-moment correlation with FIM = -0.84
Correlates poorly with London Handicap Scale (LHS), SF-36 for the physical component summary score (PCS), SF-36 for the mental component summary score (MCS), the General Health Questionnaire (GHQ), and age
- Adequate product-moment correlation with LHS = -0.33
- Poor product-moment correlation with SF-36 MCS = -0.22
- Poor product-moment correlation with SF-36 GHQ = -0.06
- Poor product-moment correlation with psychological well-being = 0.06
- Poor product-moment correlation with age = -0.001
*Since a lower score on the EDSS indicates better health, a negative correlation with EDSS occurs when a lower score indicates worse health on the measure being compared

Floor/Ceiling Effects

Multiple Sclerosis: (Hobart et al., 2000); n = 137

Excellent 0% floor effect
Excellent 0% ceiling effect

Responsiveness

Multiple Sclerosis: (Sharrack et al., 1999; n = 25; median age = 36 years; age range = 24-51; assessed during 9-month follow-up period)

EDSS is not sensitive to clinical change (effect size 0.11, P = 0.051)
FS is unresponsive in all systems except mental is weakly responsive (effect size 0.38, P = 0.012)

Multiple Sclerosis: (Hobart et al., 2000; n = 64)

EDSS had a small change with effect size = 0.1

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