Exploring the construct validity and reliability of sensor-based measurements derived from active motor assessments in adult walkers with SMA

The DigiNOA study [NCT05109637] is designed to test whether sensor-derived measurements (SDMs) from active motor assessments (AMAs) using smartphone technology have the potential to provide relevant information about disease state in adult people with Spinal Muscular Atrophy (SMA). We analyzed the test-retest reliability, and construct validity of upper limb and lower limb SDMs collected during a period of ∼30 days in 13 adult ambulatory people with SMA (aaPwSMA) (mean age: 40.5 years, 53.8% female). Test-retest reliability was assessed by the intraclass correlation coefficients (ICCs) from SDMs captured in remote-unsupervised AMAs. We observed ICCs ranging from .64 - .95 from both upper limb (ULF) and lower limb (LLF) function SDMs. Among the highest observed ICCs, we found a) the inter-typing interval (ITI) and reaction time (RT) from the Typing Test (.95 & .94) for ULF; and b) the stride duration (SD) and step power (SP) from the digital six-minutes’ walk test (d6MWT) (.81 & .89, respectively) for LLF. We evaluated construct validity by calculating the correlation coefficient's (CCs) between scores of in-clinic standard assessments and SDMs captured in AMAs at the same day in clinic. For the Typing Test SDMs, the CCs for ITI and RT were - .59 and - .62 against the Hammersmith Functional Motor Scale Expanded (HFMSE), respectively. For the d6MWT SDMs, the CCs for SD and SP were - .72 and .60 against the HFMSE respectively; and - .92 and .69 against the standard 6MWT, respectively. In a small, but homogenous, aaPwSMA group, different SDMs from AMA displayed high reliability for remote-unsupervised assessments, and moderate to good associations with in-clinic standard assessments. Given the promising results, further exploration of these tools in different functional subtypes of adult people with SMA may allow to expand our repertoire of available measurements, thus, to enrich our understanding of the heterogenous SMA disease trajectories in adulthood. The DigiNOA study [NCT05109637] is designed to test whether sensor-derived measurements (SDMs) from active motor assessments (AMAs) using smartphone technology have the potential to provide relevant information about disease state in adult people with Spinal Muscular Atrophy (SMA). We analyzed the test-retest reliability, and construct validity of upper limb and lower limb SDMs collected during a period of ∼30 days in 13 adult ambulatory people with SMA (aaPwSMA) (mean age: 40.5 years, 53.8% female). Test-retest reliability was assessed by the intraclass correlation coefficients (ICCs) from SDMs captured in remote-unsupervised AMAs. We observed ICCs ranging from .64 - .95 from both upper limb (ULF) and lower limb (LLF) function SDMs. Among the highest observed ICCs, we found a) the inter-typing interval (ITI) and reaction time (RT) from the Typing Test (.95 & .94) for ULF; and b) the stride duration (SD) and step power (SP) from the digital six-minutes’ walk test (d6MWT) (.81 & .89, respectively) for LLF. We evaluated construct validity by calculating the correlation coefficient's (CCs) between scores of in-clinic standard assessments and SDMs captured in AMAs at the same day in clinic. For the Typing Test SDMs, the CCs for ITI and RT were - .59 and - .62 against the Hammersmith Functional Motor Scale Expanded (HFMSE), respectively. For the d6MWT SDMs, the CCs for SD and SP were - .72 and .60 against the HFMSE respectively; and - .92 and .69 against the standard 6MWT, respectively. In a small, but homogenous, aaPwSMA group, different SDMs from AMA displayed high reliability for remote-unsupervised assessments, and moderate to good associations with in-clinic standard assessments. Given the promising results, further exploration of these tools in different functional subtypes of adult people with SMA may allow to expand our repertoire of available measurements, thus, to enrich our understanding of the heterogenous SMA disease trajectories in adulthood.