A Rasch analysis for classification of systemic lupus erythematosus and mixed connective tissue disease.

The classification of rheumatic diseases is challenging because these diseases have protean and frequently overlapping clinical and laboratory manifestations. This problem is typified by the difficulty of classification and differentiation of two prototypic multi-system autoimmune diseases, Systemic Lupus Erythematosus (SLE) and Mixed Connective Tissue Disease (MCTD). The researchers submitted medical risk factor data represented by instrument or laboratory measures and physician judgments (12 key features for SLE) from 43 patients diagnosed with SLE and 12 key features for MCTD from 51 patients diagnosed with MCTD to the WINSTEPS Rasch analysis program. Using Rasch model parameterization, and fit and residuals analyses, the researchers identified separate dimensions for MCTD and SLE, thereby lending support to the position that MCTD is its own separate disease, distinct from SLE.