ObjectiveTo compare the clinical characteristics,high-resolution computed tomography (HRCT) manifestations,pulmonary function results,serum autoantibodies and treatment modality of connective tissue diseases related interstitial lung diseases (CTD-ILDs) and idiopathic interstitial pneumonias (ⅡPs). MethodsPatients explicitly diagnosed with CTD-ILDs and ⅡPs were retrospectively selected from Nanjing Drum Tower Hospital between January 2004 and December 2012.The clinical features were abstracted,including age,gender,symptoms,signs,serum autoantibody results,HRCT findings,and treatment.Patient characteristics were compared between CTD-ILDs and ⅡPs using a Pearson's χ2 test for categorical variables,and a Student's t test for continuous variables. ResultsA total of 692 patients with complete data were included in this study,with 240 CTD-ILDs cases and 452 ⅡP cases.CTD-ILDs could exist in different types of CTDs,which were mainly shown in Sjogren's syndrome,rheumatoid arthritis,and dermatomyositis/polymyositis.Age,gender,connective tissue diseases related characteristics such as dry eyes,dry mouth,and arthralgia,and several autoantibodies such as ANA,SSA,SSB all showed significantly difference between CTD-ILDs and ⅡPs (P<0.05).However there were no significant differences in cough,dyspnea after exertion,velcro crackles on auscultation,or finger clubbing between two groups (P>0.05). The HRCT manifestations of CTD-ILDs were reticular opacities,patchy consolidation,band-like shadows,and pleural thickening.Pulmonary function tests commonly showed restrictive lung function and decreased diffusing capacity.The histopathologic findings of lung biopsies of CTD-ILDs were mostly chronic inflammatory cell infiltration,as well as hyperplasia of fibrous tissue and septal thickness.The finding of chronic inflammatory cell infiltration showed significant difference between CTD-ILDs and ⅡPs (P<0.05),while the HRCT manifestations,pulmonary function results or other histopathologic findings did not(P>0.05).The current treatment modality was corticosteroids plus immunosuppressants. ConclusionDespite the similarities,CTD-ILDs show distinct clinical,laboratory and imaging features from from ⅡPs in clinical practice.