Figures
- FIGURE 1
Algorithm for the diagnosis of hypersensitivity pneumonitis (HP). Reproduced from [1] with permission. #: exposure assessment includes a thorough clinical history and/or serum immunoglobulin G testing against potential antigens associated with HP and/or, in centres with the appropriate expertise and experience, specific inhalational challenge testing. ¶: high-resolution computed tomography (HRCT) should be performed using the technique described in the guidelines and then reviewed with a thoracic radiologist. +: transbronchial lung biopsy (TBLB) is suggested for patients with potential non-fibrotic HP. §: transbronchial lung cryobiopsy (TBLC) is suggested for patients with potential non-fibrotic HP, depending on local expertise. ##: surgical lung biopsy (SLB) is infrequently considered in patients with non-fibrotic HP. BAL: bronchoalveolar lavage.
- FIGURE 2
High-resolution computed tomography (HRCT) findings in hypersensitivity pneumonitis (HP). a) The reaction to inhaled antigens leads to bronchiolocentric inflammation, which on computed tomography can be seen as ill-defined centrilobular ground-glass nodules. b) Narrowing of the involved small airways by the inflammatory process may lead to retained air in the involved lobules on expiratory scans (air-trapping). The involved lobules appear darker on the expiratory scan (*). c) Diffuse interstitial inflammation leads to an increase in lung density with visibility of vessels and bronchial walls and is called ground glass. d) In HP, lobular areas with ground glass are frequently intermixed with lobules of normal appearance, leading to a patchwork of lobules with differing density, which is called mosaic attenuation. e) A patchwork of lung lobules with normal density, with lobules with ground-glass attenuation and lobules with decreased density and decreased vessel size due to air-trapping is called the “three-density pattern” and is the most specific sign for HP on HRCT. This pattern is more accentuated on expiratory scans.
- FIGURE 3
Typical fibrotic hypersensitivity pneumonitis on high-resolution computed tomography. Computed tomography (CT) scan of a 64-year-old male patient. a) Axial CT scan. b) Coronal CT scan. Mosaic attenuation at inspiration affecting all lung zones with signs of fibrosis (traction bronchiectasis) with no features suggesting an alternative diagnosis.
- FIGURE 4
Diagnostic algorithm for hypersensitivity pneumonitis (HP) in patients with no indication for lung biopsy based on the CHEST guidelines. Reproduced and modified from [2] with permission. BAL: bronchoalveolar lavage; HRCT: high-resolution computed tomography; MDD: multidisciplinary discussion.
Tables
- TABLE 1
Factors associated with mortality in patients with HP
Intrinsic factors Older age Male sex Genetic predisposition Exposures Unidentifiable inciting antigen Duration of exposure to inciting antigen History of smoking Physiology Low FVC Low DLCO Decline in FVC Lower BAL lymphocytosis Radiology Presence of fibrosis on HRCT Extent of fibrosis on HRCT UIP pattern on HRCT Histology UIP pattern Fibrotic NSIP pattern BAL: bronchoalveolar lavage; DLCO: diffusing capacity of the lungs for carbon monoxide; FVC: forced vital capacity; HRCT: high-resolution computed tomography; NSIP: non-specific interstitial pneumonia; UIP: usual interstitial pneumonia.
