Nonspecific interstitial pneumonitis (NSIP) is most likely to be confused with usual interstitial pneumonitis (UIP). Unlike patients with UIP, the majority of patients with NSIP have a good prognosis, with most patients improving after treatment with corticosteroids. Therefore it is clinically important to differentiate NSIP from UIP. UP to now, the only means of differentiating these two diseases was by means of surgical lung biopsy. American Thoracic Society (ATS) proposed a clinical diagnostic criterial for UIP to provide assistance to clinicians in its diagnosis without surgical lung biopsy. This study is aimed to investigate whether there were clinical and radiological differences between NSIP and UIP, and the usefulness of ATS clinical diagnostic criteria for UIP in Korea.

we studied 60 patients with UIP and NSIP confirmed by surgical lung biopsy. Clinical manifestations, pulmonary function test, arterial blood gas analysis, bronchoalveolar lavage (BAL), and high resolution computed tomography (HRCT) were evaluated and analyzed by Chi-square test or t-test. The clinical criteria for UIP proposed by ATS were applied to all patients with idiopathic interstitial pneumonia.

Forty-two patients with UIP and 18 with NSIP were pathologically identified. Among the 18 patients with NSIP (M : F = 1 : 17), the mean age was 55.2± 8.4 (44~73)yr. Among the 42 patients with UIP (M : F = 33 : 9), the mean age was 59.5±7.1 (45~74) yr (p=0.0460. Fever was more frequent in NSIP (39%) (p=0.034), but clubbing was frequently observed in UIP (33%) (p=0.023). BAL lymphocytosis was more frequent (23%) (p=0.0001) and CD4/CD8 ratio was lower in NSIP (p=0.045). On HRCT, UIP frequently showed honeycomb appearance (36 of 42 patients) through not in NSIP (p=0.0001). Six of 42 UIP patients (14.3%) met the ATS clinical criteria for IPF, and 3 of 16 NSIP patients (18.8%) met the diagnostic criteria.

Being a relatively young female and having short duration of illness, fever, BAL lymphocytosis, low CD4/CD8 ratio with the absence of clubbing and honeycomb appearance in HRCT increase the likelihood of the illness being NSIP. The usefulness of ATS clinical diagnostic criteria for UIP may be low in Korea.