Increased serum COMP predicts mortality in SSc: results from a longitudinal study of interstitial lung disease

Objectives. COMP is a regulator of assembly and maintenance of the fibrillar collagen I and II networks. Serum COMP reflects skin fibrosis in SSc. The purpose of this study was to examine whether serum COMP reflects fibrotic lung involvement in SSc patients and to study if serum COMP predicts mortality. Methods. Three overlapping cohorts of 244 SSc patients were studied. Two hundred and eighteen patients were included to study survival, 80 patients to study longitudinal changes of pulmonary function tests and 64 to study pulmonary involvement assessed by high-resolution CT (HRCT). Serum COMP was measured by ELISA. Skin involvement was assessed with the modified Rodnan skin score (mRSS). Data about survival were obtained from the central population registry. Results. Serum COMP measured within 5 years after the first non-Raynaud's manifestation was a predictor of death, and crude mortality increased by 6% for each COMP unit elevation. Serum COMP levels > 15 U/l were associated with a 3.13-fold (95% CI 1.73, 5.64; P < 0.001) increased risk of death. During the first year of follow-up serum COMP and vital capacity (VC) changed inversely (r(s) = -0.32; P = 0.005), but there were no correlations between baseline serum COMP and concurrent findings by spirometry or HRCT. Conclusion. Serum COMP early in disease is a predictor of mortality in SSc patients. Serum COMP changes in parallel with lung fibrosis as measured by VC, but the release from fibrotic skin possibly obscures the influx from the lungs and therefore serum COMP seems to have little utility as a marker of lung fibrosis.