Objective: To evaluate the performances of 4 sets of criteria proposed to define mixed connective tissue disease (MCTD): the criteria of Sharp, Alarcón-Segovia, Kasukawa, and Kahn. As anti-U1-RNP antibodies appear indispensable to establish the diagnosis of MCTD, we wished to reevaluate these sets of criteria in patients who all had anti-U1-RNP antibodies.
Methods: We analyzed clinical and biological data to find which diagnostic criteria were met by 45 patients with anti-U1-RNP antibodies. We tested criteria for rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, polymyositis, Sjögren's syndrome, and 4 sets of criteria for MCTD.
Results: The criteria that best identified patients with MCTD were those proposed by Alarcón-Segovia, with 62.5% sensitivity and 86.2% specificity, comparable to Kahn's criteria. The overlap with other connective tissue diseases was found to be 16%. These results could be improved by using the term "myalgia" instead of "myositis" in the definition. This increased sensitivity to 81.3%, with no decrease in specificity.
Conclusion: Alarcón-Segovia's and Kahn's criteria are the best classification criteria to define MCTD.