[Clinical significance of serum KL-6 and SP-D for the diagnosis and treatment of interstitial lung disease in patients with diffuse connective tissue disorders].

Objective: To elucidate the clinical significance of serum KL-6 and SP-D for the diagnosis and treatment of interstitial lung disease in connective tissue disorders.

Methods: 139 patients with various connective tissue disorders were subjected for the study, which included 46 cases of rheumatoid arthritis, 43 cases of Sjögren's syndrome, 16 cases of SLE, 10 cases of systemic sclerosis, 9 cases of polymyositis/dermatomyositis, 6 cases of vasculitis syndrome, 5 cases of Behçet's disease and 4 cases of MCTD. Serum levels of KL-6 and SP-D were determined by enzyme-immunoassay. The sensitivity, specificity and accuracy of serum KL-6 and SP-D for the diagnosis of interstitial lung disease were compared with serum LDH. The relationship of serum KL-6 and SP-D levels with high resolution CT (HRCT) of the lung and Gallium scintigraphy findings was analyzed. In some cases, serum levels of the two markers were determined monthly in the course of the disease.

Results: When the serum levels of KL-6 and SP-D were measured simultaneously, the sensitivity to diagnose interstitial lung disease was 67.7%, the specificity was 98.1%, and the accuracy was 91.4%, while those of serum LDH were 45.2%, 88.9%, 79.1% respectively. In the patients with interstitial lung disease, those who had elevated serum levels of both KL-6 and SP-D showed parenchymal collapse opacity-dominant pattern in HRCT. On the other hand, the patients with interstitial lung disease who had normal levels of serum KL-6 and SP-D or had elevation either in KL-6 or SP-D levels showed ground glass opacity-dominant pattern in HRCT. There was no significant correlation between serum marker levels and Gallium scintigraphy findings. When serum KL-6 and SP-D were measured monthly, the levels of both markers changed more specifically and sensitively to the lung disease activity compared with serum LDH.

Conclusions: Serum KL-6 and SP-D are more specific and useful markers for the diagnosis and evaluation of interstitial lung disease compared with serum LDH in connective tissue disorders.