Imaging of Hypersensitivity Pneumonitis

Abstract

The management of hypersensitivity pneumonitis (HP) depends on early identification of the disease process, which is complicated by its nonspecific clinical presentation in addition to variable and diverse laboratory and radiologic findings. HP is the result of exposure and sensitization to myriad aerosolized antigens. HP develops in the minority of antigenic exposures, and conversely has been documented in patients with no identifiable exposure, complicating the diagnostic algorithm significantly. Prompt diagnosis and early intervention are critical in slowing the progression of irreversible parenchymal damage, and additionally in preserving the quality of life of affected patients.

When pneumonia is not COVID-19

“…Hypersensitivity pneumonitis exhibits variable clinical and radiological signs. 66 In its acute or subacute presentation, centrilobular nodules with ground-glass attenuation and a mosaic or hog's head cheese pattern are characteristic findings of the disease. 67 Of these, the latter, with normal pulmonary lobules alternating with others of less attenuation due to air trapping as well as areas of greater ground-glass attenuation, is the one that could more often simulate SARS-CoV-2 pneumonia.…”

Practical guide for pediatric pulmonologists on imaging management of pediatric patients with COVID‐19

“…CXR is less sensitive than CT for the detection of HP. On chest CT, acute HP presents with bilateral upper lung predominant ground-glass opacities and/or poorly defined centrilobular nodules 50,51 (Figure 9).…”

“…[16][17][18]30,31 Areas of lobular air-trapping may also be observed in the sub-acute form. 51 In fever, weight loss). 54 The most frequent pattern of imaging abnormality is bilateral symmetric ground-glass opacities and/or consolidation in a lower-lobe distribution with relative subpleural sparing.…”

“…CXR is less sensitive than CT for the detection of HP. On chest CT, acute HP presents with bilateral upper lung predominant ground‐glass opacities and/or poorly defined centrilobular nodules 50,51 (Figure 9). Such ground‐glass opacities are one of the most frequently observed imaging findings in pediatric patients with COVID‐19 pneumonia and can be an overlapping imaging finding with acute HP 16‐18,30,31 .…”

A Pathophysiological Perspective on COVID-19's Lethal Complication: From Viremia to Hypersensitivity Pneumonitis-like Immune Dysregulation

“…Acute HP symptoms such as fever and cough often resemble influenza, and continued exposure to an allergen can drive progression toward chronic disease [ 14 ]. Subacute HP displays similar symptoms as acute forms, except that the lung pathology escalates toward intersitial infiltrates with bronchiolitis and GGO exhibiting centriobular nodules [ 13 15 ]. Chronic HP shows escalated symptoms with increased lymphocyte, mast cell, and eosinophil infiltration into the lungs with neutrophil activity.…”