Neutrophil lymphocyte ratio as a marker of skin disease activity in older children with juvenile dermatomyositis

Neutrophils contribute to the pathogenesis of many autoimmune diseases. While the neutrophil to lymphocyte ratio (NLR) is associated with disease activity in adult dermatomyositis, its clinical utility in juvenile dermatomyositis (JDM) is unknown. Demographic, medication use, autoantibody profile, disease activity markers, and laboratory data from 97 JDM patients was collected using retrospective chart review. Patients were age-stratified (0–9 vs. 9–21 years of age), as white blood cell count stabilizes at 9 years. The relationships between NLR with JDM disease activity measures were analyzed using spearman’s correlation. Patients were primarily white (56.7%) and female (71.1%). Older children had lower physician global assessment (PGA) (2.0 vs. 4.0, p = 0.015) and lymphocyte count (1700 vs. 2320, p = 0.01), and higher manual muscle testing (MMT-8) (80 vs. 73, p < 0.001) and childhood myositis assessment score (CMAS) (49 vs. 45, p = 0.012). Cutaneous dermatomyositis disease area and severity index (CDASI) (r = 0.39, p = 0.007) and PGA skin (r = 0.52, p = 0.004) were associated with NLR in older children, independent on prednisone use. In younger children, skin involvement was negatively associated with NLR (r=-0.41, p = 0.024). No associations with muscle activity, including CMAS (r = 0.021, p = 0.91 vs. r = 0.25, p = 0.22), CK levels (r = 0.23, p = 0.11 vs. r=-0.041, p = 0.79), and MMT-8 (r = 0.152, p = 0.31 vs. r=-0.132, p = 0.377) were seen in older or younger children respectively. Age-related variability in lymphocytes may complicate the interpretation and assessment of NLR in young children. NLR may serve as a cutaneous disease activity marker in older JDM patients. Larger multi-center cohorts are necessary to validate these findings and assess the role of treatment on NLR.