Duration of illness is an important variable for untreated children with juvenile dermatomyositis.

Objective: To evaluate the impact of duration of untreated symptoms in children with juvenile dermatomyositis (JDM) on clinical and laboratory status at diagnosis.

Study Design: We examined physical and laboratory data from the first physician visit for 166 untreated children with JDM. Disease activity scores (DASs) assessed skin and muscle involvement. Height and weight were compared with the National Health and Nutrition Examination Survey III dataset. Duration of untreated illness was designated as the time from first sign of rash or weakness to diagnostic visit.

Results: Boys and girls with untreated JDM were shorter and lighter than national norms (P > .0005 for both), and nonwhite children were weaker than white children (P > .0005). Older children had more dysphagia (P = .017) and arthritis (P > .001). Duration of untreated JDM was negatively associated with DAS weakness (P > .0005), unrelated to DAS skin, and positively associated with pathological calcifications (P = .006). With untreated disease > or = 4.7 months, serum levels of 4 muscle enzymes (aldolase, lactic dehydrogenase, creatine kinase, serum glutamic-oxaloacetic transaminase/aspartate aminotransferase) tended toward normal (P > .01 for each).

Conclusions: Duration of untreated symptoms is an important variable and should be included in decisions concerning both diagnostic criteria and intensity of therapy for children with JDM.