Wrist-worn accelerometer as innovative tool for longitudinal follow-up of idiopathic inflammatory myopathy patients: A pilot study

Idiopathic inflammatory myopathies (IIM) are disabling diseases. Disabilities may be due to muscular manifestations and/or to extra-muscular manifestations. Clinical tools for strength evaluation lack of reproducibility, and global extra-muscular assessment implies complex scores. In addition their ability to reflect the impact of the disease in the daily life remains elusive. An objective, simple and reliable tool is needed, especially regarding future clinical trials. Accelerometry provides the opportunity to objectively monitor motor activity over days during daily-life of patients. We aimed at testing accelerometer measurements to assess the changes in global physical activity of patients after treatment initiation. We have initiated a pilot study including five patients recently diagnosed for IIM. A wrist-worn accelerometer recording 15 days per month (study duration 6 months) was used after the initiation of treatment. The global movement quantity was obtained by computing the norm of the acceleration vector over recording days. Mean age of the patients was 47.7 years (Dermatomyositis = 1; Necrotizing myopathy = 3; Anti-synthetasis syndrome n = 1). The mean manual muscle testing score (8 muscle groups: MMT8) was 117/150. CK level was 3689 UI/L. At baseline, global movement quantity was significantly lower by 75% in IIM patients compared to age and sex matched control groups. After one month of treatment, the global movement quantity increased by 15.6% on average,whereasMMT8score increased by 6.4% and CK level decreased by 76.4%. These preliminary results showed that severe impairment of activity occurs in IIM patients, revealing more disabilities than MMT8 could suggest. Early important improvement of activity is detected after only one month of treatment whereas MMT changes are low. Together these results suggest that wrist-worn accelerometry is a promising objective and robust tool for home-monitoring of physical activity in patients with myositis.