Background: Multiple sclerosis (MS) is increasingly prevalent among older adults, and this results in the cumulative effects of aging and MS on mobility disability. The Patient-Determined Disease Steps (PDDS) is a patient-reported outcome measure of mobility disability in adults with MS, but its validity has not been established in older adults. This study validated the PDDS in older adults with MS by examining correlations with conceptually-relevant objective and subjective measures, including neuroimaging markers.

Methods: The sample included older adults with MS (N = 87, mean age = 64.67 ± 4.24yrs, percent female = 65.5). Primary outcome measures for validation included the Timed 25-foot Walk (T25FW), Short Physical Performance Battery (SPPB), University of Alabama at Birmingham Life-Space-Assessment scale (UAB-LSA), Nine-Hole Peg Test (9HPT), oral Symbol-Digit Modalities Test (Oral SDMT), and Fatigue Severity Scale (FSS). Structural measures of brain integrity, evaluated via 3T MRI, included grey matter volumes (thalamus, caudate, putamen, globus pallidus, hippocampus), and total white matter lesion load (WMLL). Spearman correlations were used for analyses based on non-normality of the data.

Results: Higher PDDS scores were significantly correlated with slower walking speed (T25FW time: ρ= 0.664, p < .001), worse lower extremity functioning (SPPB: ρ= -0.540, p < .001), poor fine motor dexterity (9HPT time) bilaterally (dominant hand: ρ= 0.367, p < .001; non-dominant hand: ρ= 0.263, p= .014), worse fatigue (FSS: ρ= 0.383, p < .001), and lower community mobility (UAB-LSA: ρ= -0.586, p < .001). Higher PDDS scores were also associated with lower grey matter volume in the caudate (ρ= -0.218, p= .042), putamen (ρ= -0.226, p= .036), and hippocampus (ρ= -0.213, p= .047). There were no significant correlations with WMLL, Oral SDMT, or socio-demographic covariates.

Conclusions: The PDDS is a valid self-report measure of MS-related disability in ambulatory older adults with MS.