Cryptogenic organizing pneumonia

Cryptogenic organizing pneumonia
Other names	Bronchiolitis obliterans with organizing pneumonia, idiopathic interstitial pneumonia[1]
Micrograph showing a Masson body (off center left/bottom of the image – pale circular and paucicellular), as may be seen in cryptogenic organizing pneumonia. The Masson body plugs the airway. The artery associated with the obliterated airway is also seen (far left of the image). H&E stain.
Specialty	Pulmonology
Symptoms	cough, labored breathing, fever, fatigue, unexpected weight loss[1]

Cryptogenic organizing pneumonia (COP), formerly known as bronchiolitis obliterans organizing pneumonia (BOOP), is an inflammation of the bronchioles (bronchiolitis) and surrounding tissue in the lungs.^[2][3] It is a form of idiopathic interstitial pneumonia.^[4]

It is often a complication of an existing chronic inflammatory disease such as

The clinical features and radiological imaging resemble infectious pneumonia. However, diagnosis is suspected after there is no response to multiple antibiotics, and blood and sputum cultures are negative for organisms.

Terminology

"Organizing" refers to unresolved pneumonia (in which the alveolar exudate persists and eventually undergoes fibrosis) in which fibrous tissue forms in the alveoli. The phase of resolution and/or remodeling following bacterial infections is commonly referred to as organizing pneumonia, both clinically and pathologically.

The American Thoracic Society and the European Respiratory Society hold that "cryptogenic organizing pneumonia" is the preferred clinical term for this disease for multiple reasons:^[6][7]

• Avoid confusion with bronchiolitis obliterans, which may not be visualized in every case of this disease.
• Avoid confusion with
  constrictive bronchiolitis
• Emphasize the
  cryptogenic
  nature of the disease

Signs and symptoms

The classic presentation of COP is the development of nonspecific systemic (e.g.,

• parasites
• antineoplastic drugs, erlotinib, amiodarone
• Chemical exposure, most notably to diacetyl^[10]
  • Vaping: On October 17, 2019, the American Journal of Clinical Pathology reported that lung biopsies from patients with vaping-associated pulmonary illness show acute lung injury patterns, including organizing pneumonia.^[11]
• Ionizing radiations^[12][13]
• Inflammatory diseases
  • Systemic lupus
  • Rheumatoid arthritis (RA-associated COP)
  • Scleroderma
• Bronchial obstruction
  • Proximal
    bronchial squamous cell carcinoma^[14]
• SARS-CoV-2
  • Analysis of COVID-19 CT imaging along with postmortem lung biopsies and autopsies suggest that the majority of patients with COVID-19 pulmonary involvement also have secondary organizing pneumonia (OP) or its histological variant, acute fibrinous and organizing pneumonia, which are both well-known complications of viral infections. [15]

It was identified in 1985, although its symptoms had been noted before but not recognised as a separate lung disease. The risk of COP is higher for people with inflammatory diseases like

Pulmonary function testing in people with organizing pneumonia, either cryptogenic or due to secondary causes, shows a restrictive defect with a decrease in the gas absorptive capacity of the lungs (seen as a decrease in the diffusion capacity of carbon monoxide).^[9] Airflow obstruction is usually not seen on pulmonary function testing.^[9]

Biopsy findings in patients with organizing pneumonia consist of loose connective tissue plugs involving the alveoli, alveolar ducts and bronchioles. The loose connective tissue plugs occupying the alveolar spaces often connect to other connective tissue plugs in nearby alveoli via the pores of Kohn creating a characteristic butterfly pattern on histology.^[9] There is usually minimal to no interstitial inflammatory changes in biopsies of organizing pneumonia.^[9]

Imaging

The chest x-ray is distinctive with features that appear similar to an extensive pneumonia, with both lungs showing widespread white patches. The white patches may seem to migrate from one area of the lung to another as the disease persists or progresses. Computed tomography (CT) may be used to confirm the diagnosis. Often the findings are typical enough to allow the doctor to make a diagnosis without ordering additional tests.^[19] To confirm the diagnosis, a doctor may perform a lung biopsy using a bronchoscope. Many times, a larger specimen is needed and must be removed surgically.

Plain

While patchy bilateral disease is typical, there are unusual variants of organizing pneumonia where it may appear as multiple nodules or masses. One rare presentation, focal organizing pneumonia, may be indistinguishable from lung cancer based on imaging alone, requiring biopsy or surgical resection to make the diagnosis.[20]

Complications

Rare cases of COP have induced with lobar cicatricial atelectasis.^[21]

Treatment

Systemic steroids are considered the first line treatment for organizing pneumonia, with patient's often having clinical improvement within 72 hours of steroid initiation and most patient's achieving recovery.^[22][9] A prolonged treatment course is indicated, with patients usually requiring at least 4-6 months of treatment.^[9] Patient's who are treated with larger doses of steroids require prophylaxis against pneumocystis jirovecii.^[9] Relapses may occur and are more likely to occur in severe disease or when steroids are tapered too soon or too quickly.^[9] Alternative or adjunct treatment options include macrolide antibiotics (due to anti-inflammatory properties), azathioprine and cyclophosphamide.^[9]

References