Isolated decrease of the lung diffusing capacity in patients with systemic sclerosis without pulmonary arterial hypertension: a long-term prospective study

The objective of this 5year prospective study was to investigate a clinical role of isolated decrease of DLCO in patients with systemic sclerosis (SS) without pulmonary arterial hypertension (PAH).

Methods. We selected 48 out of 142 patients with SS: 35 (73%) with limited SS and 13 (27%) with diffuse SS. The average length of the disease was 12.9 ± 7.9 years. Inclusion criteria were DLCO < 80% pred., forced vital capacity (FVC) ≥ 80% pred. and systolic pulmonary artery pressure (PAP) ≤ 35 mm Hg according to echocardiographic examination (echoCG). High resolution computed tomography (HRCT), spirometry, DLCO measurement, and echoCG were obtained at baseline and after 4.7 ± 1 year of follow up. All patients were treated with standard therapy.

Results. CT signs of interstitial lung disease (ILD) were found in 43 (89.6%) patients at baseline and newly developed in 3 other patients during the followup. During the followup, lung CT improved in 5 (10.4%) patients and progressed in 15 (31.3%) patients. Over 5 years, FVC did not change significantly (97.6 ± 10.7% and 100.8 ± 18.9%; р = 0.15), while DLCO significantly decreased both in limited and diffuse SS groups (59.8 ± 13.5% and 56.3 ± 12%; р = 0.006). Mean PAP values remained within normal range in majority of patients. Clinically significant FVC reduction (≥ 10%) was found in 5 patients; of them, CT signs of ILD at baseline were seen in 3 patients and newly developed during the followup in 2 others. Clinically significant DLCO reduction (≥ 10%) was documented in 11 (23%) patients, all had CT signs of ILD at baseline, although CT progression during the followup was noted only in six of them. Contemporary deterioration in FVC, DLCO and CT was found in 3 patients.

Conclusion. Clinical course of ILD in SS patients with isolated DLCO reduction and without PAH was relatively benign, with respiratory volumes being preserved within normal range for long time. Comparison of radiological and functional changes in a prospective study has suggested that DLCO is a more sensitive tool to determine ILD progression compared to HRCT. Regular DLCO measurements could be used as a reliable tool for monitoring of ILD associated with SS.

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