Classification criteria for systemic sclerosis (SSc) are being updated jointly by ACR and EULAR. Potential items for classification were reduced to 23 using Delphi and Nominal Group Techniques. We evaluated the face, discriminant and construct validity of the items to be further studied as potential criteria.
Face validity was evaluated using the frequency of items in patients sampled from the Canadian Scleroderma Research Group, 1000 Faces of Lupus, the Pittsburgh, Toronto, Madrid and Berlin CTD databases. SSc (n=783) were compared to 1071 patients with diseases similar to SSc (mimickers): SLE (n=499), myositis (n=171), Sjögren’s syndrome (n=95), Raynaud’s phenomenon (RP) (n=228), MCTD (n=29), and idiopathic PAH (n=49). Discriminant validity was evaluated using odds ratios (OR). For construct validity, empiric ranking was compared to expert ranking.
Compared to mimickers, SSc are more likely to have skin thickening (OR=427), telangiectasias (OR=91), anti-RNA polymerase III antibody (OR=75), puffy fingers (OR=35), finger flexion contractures (OR=29), tendon/bursal friction rubs (OR=27), anti-topoisomerase-I antibody (OR=25), RP (OR=24), finger tip ulcers/pitting scars (OR=19), anti-centromere antibody(OR=14), abnormal nailfold capillaries (OR=10), GERD symptoms (OR=8), and ANA, calcinosis, dysphagia, esophageal dilation (all OR=6), interstitial lung disease/pulmonary fibrosis (OR=5) and anti-PM-Scl antibody (OR=2). Reduced DLCO, PAH, and reduced FVC had OR<2. Renal crisis and digital pulp loss/acro-osteolysis did not occur in SSc mimickers (OR not estimated). Empiric and expert ranking were correlated (Spearman rho 0.53, p=0.01).
The candidate items have good face, discriminant and construct validity. Further item reduction will be evaluated in prospective SSc and mimicker cases.