Background/Purpose: Inclusion body myositis (IBM) is a progressive and severe inflammatory muscle disease that primarily affects adults over 50 years of age. It presents with asymmetric weakness, particularly in the quadriceps and finger flexors, and leads to significant disability over time. Standard clinical measures may not fully capture real-world activity and function. Actigraphy, a non-invasive tool for monitoring continuous physical activity, has been utilized in other myopathy subtypes but remains understudied in IBM, where it may offer valuable additional insights. This study examined the relationship between clinical assessments and actigraphy-derived activity metrics in individuals with IBM.

Methods: We conducted a pilot prospective cohort study at an academic center. Participants met the European Neuromuscular Center Classification (2024) and the ACR classification criteria (2017) for IBM. Assessments included the IBM Functional Rating Scale (IBMFRS), Timed Up and Go (TUG), and wrist-worn actigraphy (24/7 for seven consecutive days). Using Spearman’s rank-order correlation, we assessed relationships between the clinical assessments (IBMFRS and TUG) and four actigraphy-derived metrics: percentage of time in moderate-to-vigorous physical activity (%MVPA), vector magnitude counts per minute (VM), average daily steps per minute, and peak 1-minute cadence.

Results: Fifteen participants (60% male, mean age 72.5 ± 5.9 years) completed the study. The mean age of symptom onset was 65.1 years, and the mean age at diagnosis was 68.9 years, indicating a diagnostic delay of ~3.8 years. The average disease duration at enrollment was 8.6 years. Participants’ IBMFRS scores averaged 27.3 ± 5.6, and mean TUG time was 21.0 ± 12.0 seconds, indicating moderate impairment. Actigraphy revealed substantial limitations in daily activities, with a mean MVPA of 19.7%, VM of 1436.2 counts/min, average daily steps of 6.9/min, and peak 1-minute cadence of 69.8 steps/min (Table 1). IBMFRS was moderately correlated with peak 1-minute cadence (ρ = 0.41, p = 0.13) and average daily steps per minute (ρ = 0.29, p = 0.30). TUG duration was inversely correlated with VM (ρ = −0.36, p = 0.20) and steps per minute (ρ = −0.32, p = 0.26), suggesting that higher physical activity is associated with better mobility (Table 2).

Conclusion: Actigraphy metrics, particularly peak 1-minute cadence and steps per minute, demonstrated promising correlations with functional outcomes in IBM. These findings support the potential of accelerometry to capture real-world physical function and highlight the need for validation in larger, diverse myositis cohorts to establish clinical relevance and utility.

Correlation Graphs

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/from-movement-to-meaning-exploring-physical-function-in-ibm-with-actigraphy/