Monitoring disease activity in juvenile dermatomyositis: the role of von Willebrand factor and muscle enzymes.

OBJECTIVE: To assess the usefulness of serial measurement of plasma von Willebrand factor (vWF) and serum levels of muscle enzymes in the detection and prediction of flares of disease activity in children with juvenile dermatomyositis (JDM).
METHODS: Retrospective study of serial measurements of vWF and muscle enzymes in 16 patients with JDM followed for 540 patient-months. Charts were reviewed by an investigator blinded to laboratory results, and disease flare was defined as 2 of worsening function, increasing weakness, increasing muscle enzymes, increasing medication requirements.
RESULTS: vWF was increased on at least one occasion in all but 2 patients with levels up to 4.9 IU/ml (normal 0.5 to 1.5). Laboratory evaluations were available in 23/29 disease flares. The sensitivity (0.85) and specificity (0.45) of vWF to detect disease flare were not better than that of LDH or AST even when muscle enzyme levels were excluded from flare definition. CK and ALT were not significantly associated with disease flare. The risk of flare increased 3-fold after a > 20% increase in AST levels, but vWF did not reliably predict disease flare.
CONCLUSION: Although vWF is associated with disease flares, it does not seem to offer more information than enzyme measurements. LDH and AST were most useful in the detection of a flare, while AST was the only test capable of predicting it.