Diagnosis of interstitial lung disease in patients with connective tissue disease by the diffusing capacity of carbon monoxide

To evaluate the value of diffusing capacity of carbon monoxide (CO) as a sensitive and effective test for the diagnosis of early interstitial lung disease (ILD) associated with connective tissue disease (CTD).

Ninety-three patients with CTD, which included 48 patients with systemic lupus erythematosus (SLE), 18 patients with dermatomyositis (DM), 21 patients with progressive systemic sclerosis (PSS), and 6 patients with sjogren's syndrome (SS), were studied by chest radiography, HRCT and diffusion capacity of carbon monoxide. Fifty healthy individuals were included as the control group.

Seven of the 48 (15%) patients with SLE, 3 of the 18 (17%) with DM, 8 of the 21 (38%) with PSS, and 2 of the 6 (33%) with SS were found to have ILD by chest radiography. HRCT abnormalities for ILD were noted in 5/14 (36%) of the patients with SLE, 4/11 (36%) with DM, 5/12 (42%) with PSS, and 2/3 (67%) with SS. Alternation in D(L)CO was present in 20 (42%) patients with SLE, 7 (39%) with DM, 11 (52%) with PSS and 3 (50%) with SS. The means of D(L)CO were (81 +/- 26)% in SLE, (79 +/- 19)% in DM, (76 +/- 25)% in PSS and (76 +/- 11)% in SS, which were significantly different from that in the healthy controls [D(L)CO = (103 +/- 9)%] (P < 0.01).

For the diagnosis of ILD in CTD, chest radiography was less sensitive than HRCT and D(L)CO. D(L)CO, which is highly sensitive, without radioactivity and favorably accepted by patients, may be considered as the method of choice in the early diagnosis of ILD in patients with CTD.