Fig. 5: Fibrotic hypersensitivity pneumonitis (HP).

A Relationship between percent confidence in a diagnosis of fibrotic hypersensitivity pneumonitis (HP) vs usual interstitial pneumonia/idiopathic pulmonary fibrosis (UIP/IPF) and fraction of bronchioles showing peribronchiolar metaplasia. A 50% or greater fraction of bronchioles with peribronchiolar metaplasia was only seen in cases with a 60% or greater probability of fibrotic HP as determined at a special multidisciplinary discussion (see ref [20]). Note that peribronchiolar fibrosis was present in small numbers in both the fibrotic HP cases (right side of graph) and the UIP/IPF cases (left side of graph); finding only a few foci of peribronchiolar metaplasia is not helpful diagnostically. B A case that is difficult to classify. The basic pattern is that of UIP/IPF, but large blocks of fibrosis extend around bronchioles. This pattern can be seen in both UIP/IPF and fibrotic HP. C Connective tissue disease-associated interstitial lung disease (ILD). There is peribronchiolar fibrosis with almost no subpleural fibrosis. This pattern is strongly against a diagnosis of UIP/IPF but can be seen with both fibrotic HP and connective tissue disease-associated ILD. Here the numerous lymphoid aggregates (arrows), including aggregates with germinal centers (inset) strong favor a diagnosis of connective tissue disease-associated ILD. D Sarcoid. An example of sarcoid with extensive linear scarring somewhat mimicking the peribronchiolar fibrosis of fibrotic HP. However, there are numerous well defined granulomas, some with concentric fibrosis (not visible at this magnification); fibrotic HP cases do not show these features.