Evaluating Disease Activity Outcome Variables in Juvenile Dermatomyositis

The results of a large multicenter study published in Arthritis Research & Therapy demonstrated that the signs and symptoms of juvenile dermatomyositis can be used to stratify patients and establish treatment plans that correlate with disease activity. Furthermore, the study found that information provided by the physician’s global assessment of disease activity (PGA) remains an important outcome variable, while the childhood myositis assessment score (CMAS) and manual muscle testing of 8 muscle groups (MMT8) could be simplified.

Juvenile dermatomyositis is a heterogeneous disorder with varying degrees of disease severity and patterns of muscle, skin, and internal organ involvement. Between 24% and 40% of patients have a single-cycle disease course, while 50% to 60% have chronic disease activity. The mortality rate is between 2% and 3%. Given the possible long-term consequences and complications, effective management of juvenile dermatomyositis is essential. Patients with high disease activity and potentially serious complications should be treated early and aggressively, whereas patients with less severe forms of the disease should receive less aggressive therapy. Therefore, determining clinical signs and symptoms associated with more aggressive disease is crucial.

Researchers conducted a cohort study of 340 patients with juvenile dermatomyositis in order to develop a Bayesian model of disease activity using creatine kinase (CK), CMAS, MMT8, and PGA. They found that myalgia and dysphonia were associated with higher levels of disease activity on all outcome variables. Signs associated with higher PGA included periorbital rash, rash on the trunk, rash over large joints, nail fold changes, and facial swelling. They noted an association between periorbital rash, higher CK and lower CMAS and nail fold changes with lower CMAS. They also found an association between contractures with lower CMAS and MMT8 and higher PGA scores. Scores for CMAS and MMT8 correlated, while PGA was the most likely to be abnormal even when the other 3 variables were normal.

According to the authors, the correlation between higher CK values and periorbital rash and nail fold changes suggests that ongoing skin disease, accounted for only in the PGA, reflects ongoing systemic disease activity. The finding that at some patient visits the CMAS, CK, and MMT8 were normal while the PGA was abnormal suggests that the PGA measures features of juvenile dermatomyositis not captured by the other 3 assessment tools. In contrast, CMAS and MMT8 demonstrated a substantial degree of overlap in signs and symptoms measured, suggesting that these tools could be shortened, or as the authors suggest, summarized into a single instrument. In contrast, the PGA should assume greater importance in the evaluation of disease remission.

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Reference

Dijkuizen EHP, De Iorio M, Wedderbum LR, Deakin CT, on behalf of the JDRG. Clinical signs and symptoms in a joint model of four disease activity parameters in juvenile dermatomyositis: a prospective, longitudinal, multicenter cohort study.  Arthritis Res Ther. 2018;20:180.