Diffusing capacity (DLCO) as a potential surrogate marker for scleroderma related lung disease–data from the german network for systemic sclerosis

Background: Interstitial lung disease (ILD) is common in patients with systemic sclerosis (SSc), significantly limiting quality of life and survival. Data on clinical correlations between lung function, SSc phenotypes and early diagnosis of pulmonary involvement are sparse. Methods: SSc patients within the German Network for Systemic Scleroderma were analyzed for the relationship of DLCO and clinical characteristics at baseline and follow up. Results: DLCO measurements were available for 1917 SSc patients with a total of 5597 clinical visits. At baseline, 64% of the patients had DLCO levels <75% predicted. Impaired DLCO levels were observed in 74% of dcSSc patients, in 64% of SSc-Overlap patients and in 57% of lcSSc patients (p<0.0001). Furthermore, ILD patients (80%), males (62%), patients with PH (80%), dyspnea (78%), and those with anti-topoisomerase I antibodies (71%) exhibited significantly more often DLCO levels <75% (p<0.01). Patients suffering from dcSSc had the lowest DLCO levels (mean 62%), followed by patients with SSc-Overlap syndromes (mean 67%) and lcSSc patients (mean 70%). Long-term follow-up evaluation (mean follow up, 6.0 years) showed that in comparison to lcSSc patients, dcSSc patients (OR 2.1; p<0.0001; 95% CI 1.7-2.5) and SSc-Overlap patients (OR, 1.55; p<0.0001; 95% CI, 1.2-2.0) had a significantly increased risk to decline in DLCO levels < 75%. Conclusions: Impairment of DLCO is more common and more pronounced in patients with dcSSc and SSc-Overlap Syndrome compared to lcSSc. DLCO alone may be useful for diagnosing and monitoring pulmonary involvement in SSc.