Traditionally, the Expanded Disability Status Scale (EDSS) has been used for both clinical assessment and trial outcomes. The measurement properties of the EDSS are problematic, for example, it has been shown that the EDSS inadequately captures non-motor aspects of disability (e.g. fatigue, detrusor failure, pain, sexual dysfunction). An outcome which measures all aspects of disability would be desirable and one such potential candidate is the World Health Organisation Disability Assessment Schedule v2.0 (WHODAS 2.0).
To assess the WHODAS 2.0 against a wide range of self-reported outcomes measuring many different aspects of functional impairment in a large MS cohort.
Self-report instruments examining: MS impact (MSIS), fatigue (NFI-MS), spasticity (MSSS), sleep dysfunction (NSI-MS), bladder function (QUALIVEEN), pain (NPS), vision (MSVQ), sexual function (MSISQ), anxiety & depression (HADS), and the WHODAS 2.0 disability scale were administered to patients with definite MS as part of the TONiC study, a multicentre, UK study of factors affecting quality of life in MS. Subject characteristics including disease subtype and EDSS level (in four bands: 0–4, 4.5–6.5, 7.0–7.5, 8.0–9.5) were determined by a physician at study enrolment. Summed raw scale scores were converted to interval level data by application of the Rasch measurement model. Relationships were visualised by box plot with appropriate statistics for detecting group difference.
Records from 5907 subjects were available for analysis. Mean age was 50.2 years, median disease duration 11.2 years. 73% were female, 66% had relapsing, 11% primary progressive and 23% secondary progressive disease. 51% were fully ambulatory (EDSS 0–4), 37% EDSS 4.5–6.5, 7% EDSS 7.0–7.5, 5% 8.0–9.5. There were significant differences in expected gradients against the WHODAS 2.0 for all of the factors measured. The relationships were preserved for all disease subtypes.
The WHODAS 2.0 not only measures physical disability as expected but also performs well to capture non-motor and psychological aspects of disability. It might be considered superior to the EDSS which, in a previous similar analysis, failed to distinguish many non-motor aspects of disability, especially in progressive disease subtypes. Prior work has shown that the WHODAS fits the Rasch measurement model and so if satisfactory minimum clinical important change and sensitivity to change can be demonstrated in MS then it could be recommended as an excellent outcome to detect disability in MS.