Clinical significance of serum surfactant protein D (SP-D) in patients with polymyositis/dermatomyositis: correlation with interstitial lung disease

Objective. To determine the clinical significance of serum surfactant protein D (SP-D) levels in patients with polymyositis/dermatomyositis (PM/DM). Methods. Serum SP-D levels were assayed using a sensitive enzyme-linked immunosorbent assay in 59 patients with PM/DM and in 29 healthy controls. Results. The serum level of SP-D was significantly higher in patients with PM/DM than in healthy controls (mean+/-s.d. 61.7+/-122.6 vs 31.0+/-12.4 ng/ml, P < 0.01). The serum SP-D level in patients with interstitial lung disease (ILD) was significantly higher than in those without ILD (118.7+/-220.2 vs 38.7+/-21.0 ng/ml, P < 0.001). Serum level of SP-D was correlated with the presence of ILD. The incidences of decreased vital capacity (%VC) and of decreased diffusing capacity of carbon monoxidase (%DLCO) were also significantly greater in patients with an elevated SP-D level than in those with a normal level (64 vs 7%, P < 0.02; 73 vs 27%, P < 0.01). Moreover, the serum SP-D level was inversely correlated with %VC (r=-0.452, P < 0.01) and %DLCO (r=-0.349, P < 0.05). Conclusion. The serum SP-D level may be a useful marker for ILD in patients with PM/DM.