The arthropathy of systemic sclerosis (scleroderma); comparison with mixed connective tissue disease

Arthritis in systemic sclerosis (PSS) can be prominent and an overlap with rheumatoid arthritis (RA) has sometimes been queried. We therefore analysed the pattern of joint involvement of hands and wrists in 34 patients (1 male) with PSS and compared it with that of 9 patients with mixed connective tissue disease (MCTD), a condition with distinct overlap features. Although MCTD patients were younger, disease duration was similar in both groups. Extra-articular radiological findings such as calcinosis, pulp atrophy and tuft resorption were present in over half the patients with PSS but were less frequent in MCTD. Marginal erosions occurred in over 50% and ulnar styloid erosions in 35% of the PSS patients. Erosions of the 1st CMC joint were seen in one-third of them and were unrelated to age. Erosions did not correlate with clinical synovitis, the presence of rheumatoid factor which was present in 26% of PSS patients or the presence of anti-centromere or anti-Scl-70 antibodies. Erosions in MCTD patients occurred frequently and were more destructive and rapidly progressive. Correlation between erosions, rheumatoid factor and clinical arthritis was high. We conclude that erosions in PSS are frequent. Their pattern is varied but usually discrete and seldom destructive. They are not related to arthritis or serological abnormalities and may be due to several mechanisms aside from synovitis. In contrast, erosions in MCTD are more frequently destructive and related to arthritis and rheumatoid factor, suggesting a true overlap.