Is MCTD a distinct entity? Comparison of clinical and laboratory findings in MCTD, SLE, PSS, and RA patients.

Eighteen patients diagnosed as suffering from MCTD were reexamined during follow-up (mean duration 4.6 years). The clinical features of these patients were compared with those of 19 patients with systemic lupus erythematosus (SLE), 11 with progressive systemic sclerosis (PSS) and 22 with rheumatoid arthritis (RA). Considerable overlapping of abnormal features was found between MCTD and the other syndromes. At the end of the follow-up period, 70 per cent of the cases initially diagnosed as MCTD evolved to a more classical connective tissue disease, i.e., either PSS or SLE. Generally, however, the clinical evolution of the individual MCTD patient was not predictable. Abnormal aortic valve calcifications were found in the MCTD group. Four of the 18 MCTD patients were anti-RNP negative at reexamination. There was a tendency for HLA antigens B7 and B8 to be increased in the MCTD group, but this difference was not statistically significant. Three MCTD patients died before they could be reexamined (two of them from pulmonary hypertension with proliferative endarteritis of the lung vessels and one from septicaemia and multiple cerebral infarctions.