Cryptogenic organizing pneumonia overview

# Overview
Cryptogenic organizing pneumonia is an idiopathic diffuse interstitial lung disease that affects the distal bronchioles, respiratory bronchioles, alveolar ducts, and alveolar walls. The injury occurs within the alveolar wall. Cryptogenic organizing pneumonia has no identifiable etiology. Some of the causes of organizing pneumonia include infectious agents, drugs, inflammatory diseases, and toxic exposures. The symptoms of cryptogenic organizing pneumonia usually develop in the fifth or sixth decade of life and start with symptoms such as a cough, dyspnea, and weight loss. Cryptogenic organizing pneumonia patients have the good prognosis after the course of corticosteroids. Fatal outcome of cryptogenic organizing pneumonia is very rare. Patients with cryptogenic organizing pneumonia usually appear in mild distress. On examination, the patient is usually febrile, in tachypnea, tachycardia with the regular pulse. On lung auscultation there are bilateral vesicular breath sounds, fine crackles and wheezing is heard. On a chest X-ray in cryptogenic organizing pneumonia  findings like  consolidation, which may be  unilateral/ bilateral, migratory and affects all lung zone and foci of granulation tissue can also be seen. On CT scan findings  are subpleural and peribronchovascularconsolidation, ground-glass attenuation and nodules, irregular linear opacities, bronchial wall thickening and dilatation and reverse halo sign (atoll sign). On pulmonary function testing, the restrictive pattern is seen mostly. Corticosteroids are used as first-line treatment for patients with the symptomatic and progressive disease. Treatment is planned according to the severity of the disease. For treatment of mild disease is close monitoring is required, if there is worsening of symptoms or pulmonary function, then macrolides are used in the treatment of mild disease.For persistent or gradually worsening disease, corticosteroids are used for treatment and for severe disease cytotoxic agents are added. Relapses are common with corticosteriods therapy, azathioprine is used. Surgical treatment is preferred for focal organizing pneumonia. For preventive measures, the patient should be educated about the risk factors and signs of worsening of the disease.

# Historical Perspective
Initial descriptions of organizing pneumonia can be traced back to 1877 Paris, in the lectures of J.M. Charcot. The first report of non-infectious organizing pneumonia without an identifiable underlying etiology was published in 1983. Soon after, the term "bronchiolitis obliterans organizing pneumonia (BOOP)" was introduced. This nomenclature was abandoned in 2002 by the American Thoracic Society/European Respiratory Society International Consensus Panel and the term cryptogenic organizing pneumonia was adopted.

# Classification
There is no established system for the classification of cryptogenic organizing pneumonia.

# Pathophysiology
Cryptogenic organizing pneumonia is an idiopathic diffuse interstitial lung disease that affects the distal bronchioles, respiratory bronchioles, alveolar ducts, and alveolar walls. The injury occurs within the alveolar wall. There is proliferation of granulation tissue which involves alveolar ducts and alveoli. There are 4 phases lead to the formation of mature fibrotic bud. There are no specific laboratory findings associated with cryptogenic organizing pneumonia. If there are symptoms of fever, cough and dyspnea, then tests like CBC, creatinine, urinalysis, ESR, CRP should be done. Further tests are done to rule out the etiology of the cryptogenic organizing pneumonia.

# Causes
Cryptogenic organizing pneumonia has no identifiable etiology. Some of the causes of organizing pneumonia include infectious agents, drugs, inflammatory diseases, and toxic exposures.

# Differentiating Cryptogenic organizing pneumonia from Other Diseases

# Epidemiology and Demographics
Cryptogenic organizing pneumonia is approximately accounting to 5 to 10% of the chronic infiltrative lung disease in the United States. The incidence of cryptogenic organizing pneumonia is approximately 1.1 per 100,000 individuals in Iceland and 6-7 cases per 100,000 individuals in Canada. Cryptogenic organizing pneumonia commonly affects people of 50-60 years of age and rarely affects children. It affects men and women equally.

# Risk Factors
Common risk factors in the development of cryptogenic organizing pneumonia include infectious pneumonia, connective tissue diseases, immunologic diseases and inflammatory bowel disease, organ transplantation, medication use, breast radiation therapy and exposure to the toxin.

# Screening
There is no screening for  cryptogenic organizing pneumonia.

# Natural History, Complications, and Prognosis
The symptoms of cryptogenic organizing pneumonia usually develop in the fifth or sixth decade of life and start with symptoms such as a cough, dyspnea, and weight loss.Cryptogenic organizing pneumonia patients have the good prognosis after the course of corticosteroids. Fatal outcome of cryptogenic organizing pneumonia is very rare.

# Diagnostic study of choice
There is no diagnostic study of choice for cryptogenic organizing pneumonia.

## History and Symptoms
Patients with cryptogenic organizing pneumonia may have a positive history of connective tissue diseases, drug intake, malignancy and another interstitial lung disease. Common symptoms are a dry cough, shortness of breath, fever, fatigue and weight loss. Less common symptoms are hemoptysis, chest pain, and night sweats.

## Physical Examination
Patients with cryptogenic organizing pneumonia usually appear in mild distress. On examination, the patient is usually febrile, in tachypnea, tachycardia with the regular pulse. On lung auscultation there are bilateral vesicular breath sounds, fine crackles and wheezing is heard.

## Laboratory Findings
There are no specific laboratory findings associated with cryptogenic organizing pneumonia. If there are symptoms of fever, cough and dyspnea, then tests like CBC, creatinine, urinalysis, ESR, CRP. Further tests are done to rule out the etiology of the cryptogenic organizing pneumonia.

## Chest X Ray
Findings on a chest X-ray in cryptogenic organizing pneumonia are consolidation, which may be  unilateral/ bilateral, migratory and affects all lung zone.Foci of granulation tissue can also be seen.

## Electrocardiogram
There are no ECG findings associated with cryptogenic organizing pneumonia.

## CT
CT scan is used to diagnose cryptogenic organizing pneumonia. Various findings seen on CT scan are subpleural and 
peribronchovascularconsolidation, ground-glass attenuation and nodules, irregular linear opacities, bronchial wall thickening and dilatation and reverse halo sign (atoll sign).

## Ultrasound
There are no ultrasound associated with cryptogenic organizing pneumonia.

## Other Imaging Findings
There are no other imaging findings associated with cryptogenic organizing pneumonia.

## Other Diagnostic Studies
Pulmonary function test may be helpful in the diagnosis of cryptogenic organizing pneumonia. The most common finding in cryptogenic organizing pneumonia is mild to moderate restrictive ventilatory defect and DLCO is reduced. Flexible bronchoscopy is performed to obtain bronchoalveolar lavage sample (BAL) and transbronchial biopsy.

# Treatment

## Medical Therapy
The mainstay of the therapy is pharmacotherapy. Corticosteroids are used as first-line treatment for patients with the symptomatic and progressive disease. Treatment is planned according to the severity of the disease. For treatment of mild disease close monitoring is required, if there is  worsening of symptoms or pulmonary function, macrolides are used in the treatment of mild disease.For persistent or gradually worsening disease, corticosteroids are used for treatment and for severe disease cytotoxic agents are added. Relapses are common with corticosteriods therapy, azathioprine is used.

## Surgery
Surgical intervention is not recommended for the management of cryptogenic organizing pneumonia. Resection of the solitary nodule is the treatment for focal organizing pneumonia.

## Primary Prevention
Effective measures for the primary prevention of cryptogenic organizing pneumonia is the elimination of the cause and appropriate treatment.

## Secondary Prevention
Effective measures for the secondary prevention of cryptogenic organizing pneumonia include educating the patient about the need for early treatment to prevent long term disabling bronchiolitis obliterans and interstitial fibrosis.