Nonspecific interstitial pneumonia: clinical associations and outcomes.

BACKGROUND: Studies have shown that nonspecific interstitial pneumonitis (NSIP), even when initially diagnosed as an idiopathic form of the disease, might be associated with an autoimmune background that later reveals itself as an organ-specific or a systemic autoimmune disease.

METHODS: NSIP patients were divided into three groups. The NSIP patients who met the criteria for having a systemic autoimmune disease (SAD) were defined as the systemic autoimmune disease-associated NSIP (SAD-NSIP) group. The NSIP patients who did not meet the criteria for a systemic autoimmune disease were defined as an antibody-positive group (i-NSIP-Ab + group) if their sera were positive for autoantibodies. The NSIP patients with negative serologic tests for auto-antibodies were defined as the antibody-negative group (i-NSIP-Ab- group). The clinical characteristics were analyzed and compared among the three groups.

RESULTS: Ninety-seven NSIP patients were included. The mean age of the study population was 48 ± 11 years. The mean follow-up time was 54 ± 34 months. At the time of the surgical lung biopsies, 23/97 (23.7%) of the patients were classified as SAD-NSIP; 30/97 (30.9%) were in the i-NSIP-Ab + group; and 44/97 (45.4%) were in the i-NSIP-Ab- group. At the end of the follow-up period, three cases were diagnosed with polymyositis (one case from the i-NSIP-Ab + group, two cases from the i-NSIP-Ab- group), one with scleroderma (from the i-NSIP-Ab + group, scl-70 positive and skin biopsy) and another one with microscopic polyarteritis (from the i-NSIP-AB-group, p-ANCA and MPO positive, renal biopsy). Three cases in the i-NSIP-Ab- group were later found to be positive for autoantibodies. Due to these changes in classification, at the end of the follow-up period, the SAD-NSIP group consisted of 28/97 patients (28.9%), the i-NSIP-Ab + group of 31/97 (32.0%) and the i-NSIP-Ab- group of 38/97(39.1%). There were no significant differences in clinical manifestations, radiographic findings or pulmonary function tests among the three groups at the time of surgical lung biopsy or after reclassification after the follow-up period. SAD was an independent risk factor for the survival of the patients with NSIP after follow-up.

CONCLUSION: Follow-up is recommended because idiopathic NSIP may be the first manifestation of a systemic autoimmune disease.