Mixed (Neutrophil-Rich) Interstitial Pneumonitis in Biopsy Specimens of Lung Allografts

Study objectives: Mixed interstitial pneumonitis (MIP), defined herein as a diffuse neutrophil-rich inflammatory infiltrate within the interstitial tissues, is an uncommon finding that is not a standard manifestation of acute or chronic rejection. This study examines the clinical significance of MIP in lung allograft recipients at St. Louis University Hospital. We retrospectively reviewed surgical pathology reports from a selected 50-month period, and identified MIP reported in 13 transbronchial biopsy specimens in lung transplant recipients, representing 4.7% of all lung allograft biopsy specimens seen during this 4-year period. Biopsy specimens with MIP were examined to confirm the presence of a neutrophil-rich interstitial infiltrate and other associated histopathologic findings. The culture results, eytopathologic findings, and clinical charts of the affected patients were also reviewed. The detection of MIP at some point in a patient's posttransplant course was found to be associated with a significantly shorter (p