Follow-up of 151 patients with high-titer U1RNP antibodies.

We performed a longitudinal follow-up study of clinical findings in 151 patients with high-titer antibodies against U1 ribonucleoprotein (U1RNP) as measured by haemagglutination. Formal connective tissue disease (CTD) diagnoses were assigned and diagnostic transitions analysed. One-hundred eighteen females and 33 males entered the study; the mean duration of follow-up was 7.1 years. Mean age at entry was 34.7 years; 73% of the patients had early disease (duration < 2 years). Fifty-six patients (37%) presented with a definite diagnosis, most often mixed connective tissue disease (MCTD, n = 40), followed by systemic lupus erythematosus (SLE, n = 11) and systemic sclerosis (SSc, n = 5). Of 84 patients (56%) presenting with nonspecific symptoms of possible, "undifferentiated" CTD, 58 developed MCTD, 4 SSc and 2 SLE. By the end of the follow-up period. 127 patients had developed a well-defined CTD; final diagnoses were: MCTD (n = 97), SLE (n = 18), SSc (n = 12). We conclude that CTD in the context of high-titer anti-U1RNP antibodies may be transitive and sequential in nature, although the diagnostic criteria for MCTD previously proposed by our group seem to delimit a clinically stable condition in most patients in this subgroup.