Serum concentration of surfactant protein D in patients with systemic sclerosis: The potential marker of the interstitial lung disease severity.

Pulmonary involvement is a severe manifestation of systemic sclerosis (SSc). The study was designed to determine the serum level of surfactant protein D (SP-D) in patients with SSc in relation to clinical and laboratory parameters as well as to analyze dynamics of changes of these indices within one year of observation. SP-D was assayed in 41 patients with SSc and 15 healthy controls. Additionally, pulmonary function tests, chest high-resolution computed tomography (HRCT), and inflammatory markers were assessed. All tests were performed twice: at entry and repeated after one year of observation. The serum level of SP-D was significantly higher in patients with SSc than in healthy controls. Serum concentration of SP-D was significantly higher in patients with systemic sclerosis-related interstitial lung disease (SSc-ILD) than in those without SSc-ILD. SP-D was found to correlate with lung involvement evaluated with the Medsger score (diffusing capacity of the lung for carbon monoxide (DLCO), forced vital capacity, radiological changes, and estimated pressure in the pulmonary artery in echocardiography). SP-D correlated with the honeycombing and/or reticular pattern in HRCT and ground glass opacification pattern. Serum concentration of SP-D was elevated in patients with a decreased DLCO. Furthermore, SP-D was higher in patients with diffuse cutaneous type (dcSSc) of the disease than in those with SSc limited type (lcSSc). Because of the small size of the group, it was not possible to perform a statistical analysis for patients who had different results in HRCT, VC, and Medsger score between the first and the second evaluation. SP-D seems to be an index for assessing lung involvement. It reflects the state of pulmonary fibrosis but not the dynamics of the pulmonary fibrosis progression. Further studies are needed to evaluate clinical application of the index, and currently, there is no evidence for the recommendation of the application of SP-D in routine evaluation of patients with SSc.