Editor's Comment

In this article, Pelle and Callen report a strong association between the development of rash in patients with dermatomyositis who take hydroxychloroquine compared with similarly exposed patients with lupus. The criteria to appraise the validity of such a study about harm include similarity of the comparison groups with respect to important determinants of outcome; similar measurement of outcome and exposure in the groups; sufficient length of follow-up; and correct temporal relationship between exposure and adverse events (Levine M, Walter S, Lee H, Haines T, Holbrook A, Moyer V, for the Evidence-Based Medicine Working Group. Users' guides to the medical literature, IV: how to use an article about harm. JAMA. 1994;271:1615-1619). This study meets these quality criteria quite well. The strength of association in case-control studies is typically expressed as the odds ratio and its 95% confidence interval (12 [1.8 to 525] in this study). Pelle and Callen provide reasonable advice as to how the data should be applied to patient management. The study represents level 3B evidence (http://minerva.minervation.com/cebm/docs/levels.html) and should be confirmed by others.