There is need to respond to the challenges of developing a robust measurement technique for self-reporting of the level of physical functioning by patients with multiple sclerosis (MS) to help with identifying strategies for improving such outcome. The emergence of the NIH PROMIS item banks has opened new possibilities for developing instruments that are brief, optimally targeted and, potentially, have high precision. This holds promise for addressing unmet measurement needs in MS populations e.g. subtle physical disability changes.
To describe the development, validity and applicability of a multiple sclerosis (MS)-specific PROMIS short form for use in relapsing and progressive MS types, the PROMIS SF v2.1 – Physical Function (MS) 15a.
A mixed-methods sequential design was followed in this research. Step (1) Concept elicitation (CE) interviews were carried out with MS patients (n=14). Step (2) results from the interviews were mapped to the PROMIS physical function item bank, to identify items relevant for MS patients. Subsequently, neurologists (n=6) rated the relevance of the item pool. Step (3) cognitive debriefing (CD) interviews were performed with MS patients to confirm the comprehensiveness, relevance and language clarity of the draft short form (n=48). Step (4) Further item reduction and psychometric evaluation was performed in two observational studies [cross-sectional study at two MS tertiary centers, n=296 (US); 96-week longitudinal study in UK MS Register cohort, n=558 (UK)].
The initial item shortlist (48 items) from the NIH PROMIS item bank was revised in sequential steps, considering 1) optimization of coverage of the underlying concept, 2) results from CD interviews and 3) results from psychometric item-level analysis. Fifteen items were retained in the final short form.
Cronbach’s alpha (> 0.9) and ICC of test-retest scores (5 to 27 days) (> 0.9) indicated the short form’s strong reliability. Convergence validity was demonstrated by moderate-to-strong correlations with related PRO measures as well the EDSS (rho = ± 0.5 to 0.9). The short form discriminated between groups of patients according to levels of physical health and other criteria. A score banding system referencing responses on the individual items as anchors, was generated, to facilitate meaningful score interpretation.
The PROMIS PF (MS) 15a is a reliable and valid short form for assessing physical function with self-report in people living with MS. The inclusion of input from MS patients and neurologists during its qualitative phase of development, ensured comprehensiveness and relevance for both relapsing and progressive MS types.