Mixed connective tissue disease - a subset with sequential clinical and laboratory features.

Twenty-three patients who lacked the full picture of mixed connective tissue disease (MCTD) initially, developed new findings or experienced regression of initial features with time. Each patient had at least 1 extractable nuclear antigen (ENA) antibody titer greater than or equal to 1:10,000 composed exclusively of ribonucleoprotein; but variation in titer occurred in 9 and Sm antibody was transiently found in 3 patients. Four initially had other diagnoses and negative antinuclear antibody tests (ANA) before developing speckled ANAs. Eleven patients had consistently speckled ANAs. As suggested by earlier clinical observations, MCTD can change clinically and serologically. This study demonstrates the sequential development of the features of SLE, polymyositis, rheumatoid arthritis and in addition emphasizes the serologic studies may also vary over time in these patients.