Organizing pneumonia

Organizing pneumonia (OP) is an inflammatory disorder involving both the peripheral bronchioles and alveoli simultaneously. It has distinctive radiographic findings, histologic features, and response to corticosteroids (unlike usual interstitial pneumonia).

OP may be caused by multiple insults such as medication, infection, rheumatologic disease, autoimmune disease, post transplantation, radiation, and environmental causes. In cryptogenic organizing pneumonia, a cause cannot be elicited after a careful history, examination and pertinent laboratory studies.

High-resolution chest computed tomography scan shows bilateral patchy triangular ground-glass opacities with air bronchograms usually located peripherally.

Most often, diagnosis is made using clinico-radiologic criteria and usually in the setting of a multidisciplinary team. However, lung biopsy may be required to establish the definitive diagnosis in patients with unusual findings.

Cryptogenic OP may require treatment, and prednisone is the most commonly used drug.

For patients with secondary OP, primary management is removal of the inciting cause or treatment of the underlying disease. In some patients, corticosteroids may be indicated.

Organizing pneumonia (OP) is defined as organized polypoid granulation tissue in the terminal bronchioles, alveolar ducts and alveoli; it has distinctive radiographic findings, histologic features, and response to therapy.[1]Epler GR, Colby TV. The spectrum of bronchiolitis obliterans. Chest. 1983 Feb;83(2):161-2. https://www.sciencedirect.com/science/article/pii/S0012369215399633?via%3Dihub http://www.ncbi.nlm.nih.gov/pubmed/6822090?tool=bestpractice.com [2]Epler GR, Colby TV, McLoud TC, et al. Bronchiolitis obliterans organizing pneumonia. N Engl J Med. 1985 Jan 17;312(3):152-8. http://www.ncbi.nlm.nih.gov/pubmed/3965933?tool=bestpractice.com [3]Epler GR. Bronchiolitis obliterans organizing pneumonia, 25 years: a variety of causes, but what are the treatment options? Expert Rev Respir Med. 2011 Jun;5(3):353-61. http://www.ncbi.nlm.nih.gov/pubmed/21702658?tool=bestpractice.com The term cryptogenic is applied when a causative factor cannot be found.[Figure caption and citation for the preceding image starts]: Medium-powered pathology slide showing circular and branching bronchioles filled with polypoid plugs of granulation tissue and alveoli filled with organizing pneumoniaFrom the collection of Gary R. Epler, MD [Citation ends].

OP was previously called bronchiolitis obliterans with organizing pneumonia (BOOP) but this led to some confusion with the entirely separate disease bronchiolitis obliterans.[4]Bradley B, Branley HM, Egan JJ, et al; British Thoracic Society Interstitial Lung Disease Guideline Group, British Thoracic Society Standards of Care Committee; Thoracic Society of Australia; New Zealand Thoracic Society; Irish Thoracic Society. Interstitial lung disease guideline. Thorax. 2008 Sep;63 Suppl 5:v1-58. https://thorax.bmj.com/content/63/Suppl_5/v1.long http://www.ncbi.nlm.nih.gov/pubmed/18757459?tool=bestpractice.com Hence, a revision of the nomenclature to organizing pneumonia, cryptogenic and secondary. Some clinicians still adhere to the earlier nomenclature. The term cryptogenic organizing pneumonia (COP) is a general term referring to organized inflammatory process in the alveoli from an unknown cause.[5]Travis WD, Costabel U, Hansell DM, et al. An official American Thoracic Society/European Respiratory Society statement: Update of the international multidisciplinary classification of the idiopathic interstitial pneumonias. Am J Respir Crit Care Med. 2013 Sep 15;188(6):733-48. https://www.atsjournals.org/doi/10.1164/rccm.201308-1483ST http://www.ncbi.nlm.nih.gov/pubmed/24032382?tool=bestpractice.com COP is the preferred term because it captures an "acinar" rather than an airway disease, and BOOP may be confused with obliterative bronchiolitis.[4]Bradley B, Branley HM, Egan JJ, et al; British Thoracic Society Interstitial Lung Disease Guideline Group, British Thoracic Society Standards of Care Committee; Thoracic Society of Australia; New Zealand Thoracic Society; Irish Thoracic Society. Interstitial lung disease guideline. Thorax. 2008 Sep;63 Suppl 5:v1-58. https://thorax.bmj.com/content/63/Suppl_5/v1.long http://www.ncbi.nlm.nih.gov/pubmed/18757459?tool=bestpractice.com

The following are a few differences between obliterative bronchiolitis, where there is obstruction of the bronchioles due to inflammation, and organizing pneumonia. Wheezing is not a common symptom of OP; crackles, and not wheezes, are heard by auscultation in OP. The FEV1/FVC ratio is normal or slightly increased in OP, not decreased as in airway obstructive diseases and the radiographic findings show bilateral patchy infiltrates, not normal or hyperinflation seen in airflow obstructive diseases.