Background Chronic cutaneous lupus (CCLE) is a group of distinctive cutaneous lupus erythematosus (CLE) subtypes that includes discoid lupus (DLE), lupus profundus (LEP), chilblain lupus (CLE), and lupus tumidus (LET). While CCLE phenotypes can be seen in individuals with systemic lupus (SLE), patients with a diagnosis of primary CCLE can potentially fulfil the American College of Rheumatology (ACR) classification criteria of SLE without having prominent systemic manifestations. The Systemic Lupus International Collaborating Clinics (SLICC) have expanded upon the ACR criteria to address several concerns including clinical relevance. We examined the accuracy of these two sets of criteria in classifying SLE in a cohort of patients with CCLE.
Materials and methods We studied a subset of patients with CCLE enrolled in the Georgians Organised Against Lupus (GOAL) study. GOAL is a population-based cohort of people with lupus. Medical records of 90 participants who had a dermatologist-documented diagnosis of one of the CCLE subtypes and a clinical assessment by an experienced rheumatologist were reviewed to apply ACR and SLICC criteria. We examined the sensitivity and specificity for each set of criteria, using the clinical diagnosis by the attending rheumatologist as the reference standard of SLE.
Results There were 85 patients with DLE (7 with overlapping LEP), 3 with LEP, and 2 with LET. Overall, 56 patients had a diagnosis of primary CCLE and 34 CCLE with SLE. Sensitivity was 88.2% and 97.1% for ACR and SLICC, respectively; specificity was 87.5% and 80.4% for ACR and SLICC, respectively. Among 7 ACR criteria false positive cases, all had DLE and (+) ANA, 6 had photosensitivity, 4 had leukopenia, and 1 had (+) anti-Sm and (+) aPL autoantibodies. Among 11 SLICC false positives, all had DLE, 10 had (+) ANA, 7 had photosensitivity, 6 had leukopenia and 1 had anti-dsDNA, anti-Sm and anti-aPL autoantibodies. Receiving operating curves (ROC) are shown in Figure 1.
Conclusions Among individuals with a diagnosis of CCLE, SLICC and ACR criteria have excellent (97.1%) and very good (88.2%) sensitivity to classify SLE, respectively. Specificity, however, was superior for the ACR criteria. Our data indicate that nearly 20% and 13% of patients with primary CCLE would be misclassified as SLE if SLICC and ACR criteria were applied, respectively. Positive ANA, photosensitivity, leukopenia, and CCLE diagnosis are predominant manifestations in false positive cases. These findings are helpful to determine potential biases associated with the definition of CCLE in clinical and epidemiological studies.
Acknowledgements This study is supported by CDC (U01DP005119.
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