Clinicopathologic features of usual interstitial pneumonia and its differential diagnosis from idiopathic nonspecific interstitial pneumonia

Abstract

To investigate the clinicopathologic features of usual interstitial pneumonia (UIP) and its differential diagnosis from idiopathic nonspecific interstitial pneumonia (INSIP). The clinical and pathological features of 15 UIP and 11 cases of INSIP, having received open or video-assisted thoracoscopic lung biopsies and having follow-up information were reviewed. UIP occurred more often in males over 50 years of age. Clinical findings included progressive shortness of breath, cough, sputum and crackles over both lung fields. High resolution computerized tomography (HRCT) showed patchy attenuation, especially over both lower lobes. Honeycombing was found in 8 cases. Histologically, UIP was characterized by scattered fibrotic foci, fibrosis (often associated with honeycombing) and pulmonary architectural destruction. It had a heterogeneous appearance, with alternating areas of normal lung, interstitial inflammation, fibrosis and honeycomb changes. The frequencies of fibroblastic foci, muscle sclerosis, honeycomb changes, diffuse fibrosis and pulmonary architectural destruction in UIP and INSIP were 100% and 27.3% (P<0.001), 80.0% and 36.4% (P<0.05), 86.7% and 27.3% (P<0.001), 100% and 54.5% (P<0.01) and 100% and 45.5% (P<0.05), respectively. The response rate to glucocorticoid was 26.7% and 72.7% (P<0.05) in UIP and INSIP respectively. The distinction between UIP and INSIP is difficult if based on clinical examination alone. HRCT is helpful for differential diagnosis in some difficult cases. Definite diagnosis depends mainly on open lung biopsies. Key histologic features of UIP include heterogeneous appearance with interstitial inflammation, fibroblastic foci, scar formation and honeycomb changes.