['Muscle enzyme levels are insensitive markers of disease activity in juvenile and adult dermatomyositis (DM), especially during the active treatment phase. To improve our ability to monitor DM disease activity longitudinally, especially in the presence of immunomodulating agents, we prospectively evaluated whether interferon (IFN)-dependent peripheral blood gene and chemokine signatures could serve as sensitive and responsive biomarkers for change in disease activity in adult and juvenile DM.', 'Peripheral blood and clinical data were collected from 51 patients with juvenile or adult DM prospectively over 2 study visits. We performed disease activity measurements and calculated whole-blood type I IFN gene and chemokine scores. We also measured serum levels of other proinflammatory cytokines, including interleukin-6 (IL-6).', 'Changes in juvenile and adult DM global disease activity correlated positively and significantly with changes in the type I IFN gene score before adjustment for medication use (r = 0.33, P = 0.023) and with changes in the IFN chemokine score before and after adjustment for medication use (r = 0.53, P < 0.001 and r = 0.50, P < 0.001, respectively). Changes in muscle and extramuscular visual analog scale (VAS) scores correlated positively with changes in IFN gene and chemokine scores (P = 0.002, P < 0.001, P = 0.095, P < 0.001). Serum levels of IL-6, IL-8, and tumor necrosis factor α (TNFα) correlated positively with changes in global, muscle, and extramuscular VAS scores (P < 0.05).'] Are changes in novel biomarkers of disease activity in juvenile and adult dermatomyositis sensitive biomarkers of disease course?