Patients typically present in the fifth or sixth decade of life with fever, malaise, cough, and shortness of breath. Cryptogenic organizing pneumonia is unique among interstitial lung diseases in that symptoms are subacute (weeks in duration). Patients frequently fail empiric antibiotics for presumed bacterial pneumonia. Their cough may be dry or productive. Sputum may be of clear or discolored. Rarely patients develop a rapidly progressive disease with severe dyspnea and hypoxemia. Chest pain, night sweats, significant weight loss and mild arthralgias are uncommon symptoms. Hemoptysis and pneumothorax have rarely been reported.

A detailed history and physical examination should be performed to rule out connective tissue diseases, as they can be associated with organizing pneumonia. A thorough medication and exposure history should also be obtained. The respiratory exam typically discloses inspiratory crackles, but the exam can be normal.

White cell count is typically elevated with neutrophilia. Inflammatory markers, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are commonly elevated. When COP is suspected then testing for autoimmune diseases should be undertaken.

Radiography

The chest radiograph findings in COP include patchy diffuse consolidations mostly involving bilateral lower zones. Other described findings include migratory, irregular, linear, or nodular opacities. Pleural effusions can also be seen.

High-Resolution Computed Tomography (HRCT)

HRCT of the lungs reveals bilateral patchy peripherally located consolidations or ground glass opacities. These are often asymmetric. The classic HRCT sign described in COP is the atoll sign, also known as the reverse halo sign. This sign is characterized by a dense outer rim of consolidation around a focal ground-glass opacity. This sign, seen in about 20% of patients with COP and is non-specific as it can be seen in various other infectious and inflammatory conditions.

Other less common findings include irregular nodular opacities, cavitary lesions, and pleural effusions. Multiple nodules and cavitary lesions should raise suspicion for malignancy.

Pulmonary Function Testing (PFT)

PFTs typically reveal a restrictive defect with diffusion impairment. Desaturation with 6-minute walk testing is also commonly noted.

Bronchoscopy

Flexible bronchoscopy with bronchoalveolar lavage (BAL) is often performed to rule out infections, pulmonary hemorrhage, and malignancy. BAL fluid characteristically has mixed cellularity with neutrophils, lymphocytes, and eosinophils. Significant lymphocyte elevation (approximately 40%) is typical, and CD4/CD8 ratio reveals CD8 predominance. Lack of lymphocytosis on BAL portends a poor prognosis. Marked elevation of eosinophils (greater than 25%) suggests eosinophilic pneumonia or rarely an overlap phenomenon.

Lung Biopsy

Transbronchial lung biopsies may be attempted but are often inadequate to make a definitive diagnosis due to the small amount of lung tissue obtained and loss of tissue architecture from crush artifact. It can help rule out alternative diagnoses. A surgical lung biopsy is often required to make a definitive diagnosis. Wedge biopsies are preferably obtained from at least 2 lobes with distinct radiographic involvement. In patients with a convincing clinical and radiographic presentation, in whom risks of an invasive procedure outweigh benefits, treatment can be started without a lung biopsy, after discussion with the patient.

There have been no controlled trials comparing medications or duration of treatment in COP. Treatment regimens are based on consensus guidelines. The initial clinical presentation, severity of disease, and degree of responsiveness should be considered when deciding on an appropriate regimen and duration of therapy.[8][9][10][11]

Spontaneous remissions have been described for patients with mild symptoms and minimal radiographic and PFT abnormalities. The anti-inflammatory effect of macrolides particularly clarithromycin has been exploited in some reports to treat patients with mild symptoms.

The vast majority of patients with progressive symptoms and diffuse radiographic involvement are treated with oral glucocorticoids resulting in marked improvement in symptoms. British Thoracic Society guidelines recommend initiating prednisone at a dose of 0.75 to 1 mg/kg per day and weaning over 6 to 12 months. Alternative regimens include starting prednisolone at a dose of 1 to 1.5 mg/kg for 3 months and then tapering or starting methylprednisolone 0.5 to 1 g intravenously (IV) for the first 3 days followed by prednisolone at 20 mg daily, then tapering based on clinical response. Some authors have tried shorter courses tapered over 3 to 6 months with similar relapse rates. Regardless of the regimen, the initial dose is typically maintained for 4 to 8 weeks. Patients should be followed closely with follow-up clinical examination, pulmonary function testing, and chest radiographs. Relapses are common when tapering steroids but do not seem to affect the outcome. Delayed onset of initial treatment and evidence of cholestasis on laboratory testing are shown to be associated with multiple relapses. The last effective dose of glucocorticoids should be reinstituted at the earliest sign of worsening disease. Other groups have attempted lower dose of glucocorticoids with a goal of reducing cumulative steroid exposure, with slightly higher relapse rates but overall no change in morbidity and mortality. Close monitoring for adverse effects of glucocorticoids is recommended. Surgical resection is not recommended as treatment.

Patients who are unable to taper off glucocorticoids or have significant side effects to glucocorticoids can be started on a steroid-sparing agent, although COP is an unapproved indication for all steroid-sparing medications. Azathioprine and mycophenolate mofetil, among others, have been reported in case series for successful management of COP.

In patients who fail to improve despite high-dose steroid therapy, alternative diagnoses or infections should be first ruled out. Second-line agents such as cyclophosphamide and cyclosporine A have been reported to produce good clinical responses in these steroid non-responsive cases.

Variants of COP

Secondary Organizing Pneumonia

Organizing pneumonia (OP) due to a secondary cause has similar clinical, radiological, and histological features as COP; hence, these causes have to be rigorously excluded prior to diagnosing COP. Secondary OP is associated with autoimmune diseases such as rheumatoid arthritis, granulomatosis with polyangiitis and polymyositis/dermatomyositis or after radiation exposure to lung or associated with hematological malignancies or secondary to drug exposures. It is important to distinguish from COP because treatment varies and a secondary OP has a worse prognosis.

Acute Fulminant COP

Fulminant COP is suspected when patients present with rapidly-worsening respiratory failure and hypoxemia, often requiring invasive mechanical ventilation. The clinical presentation is similar to adult respiratory distress syndrome (ARDS) but histologically resembles OP without overt fibrosis. Clinically and radiographically it cannot be distinguished from acute interstitial pneumonia (AIP). Patients progress to worsening respiratory failure and have high mortality. If the diagnosis is made, reports have shown a rapid response to glucocorticoids.

Acute Fibrinous and Organizing Pneumonia (AFOP)

This rare entity presents as an acute respiratory failure but radiographically and histopathologically appears similar to organizing pneumonia. It is typically idiopathic but may be associated with collagen vascular disease, hypersensitivity pneumonitis, or drug reaction.

Fibrosing COP

Fibrosing COP is a rare entity with similar clinical and histological appearance to COP but with variable amounts of fibrosis. The fibrosis may or may not be evident radiographically but is seen on pathologic examination. These patients have a poor response to glucocorticoids or other agents. Patients often succumb to progressive respiratory failure. These cases may represent overlap with other idiopathic interstitial pneumonia.

Unifocal COP

Unifocal COP is typically diagnosed during the evaluation of a solitary pulmonary nodule concerning for lung malignancy. No relapses have been reported.

Other Causes

Infectious Causes

Bacterial, fungal, or viral pneumonia are appropriately the first considered diagnosis in a patient presenting with fever, cough, and shortness of breath along with radiographic findings.

Inflammatory Causes

Other interstitial lung diseases could give a similar radiographic appearance including idiopathic interstitial pneumonia such as NSIP and UIP. Hypersensitivity pneumonitis could have a very similar clinical presentation, but radiographic changes are usually upper lobe predominant, and there is an identifiable exposure history. Hypersensitivity pneumonitis and COP share a lymphocyte predominant BAL, but histopathology reveals chronic inflammation with poorly formed granulomas in hypersensitivity pneumonitis.

Chronic eosinophilic pneumonia has a similar clinical and radiologic presentation but is differentiated by BAL fluid or peripheral eosinophilia and histology.

Malignancy

Radiographically pulmonary malignancies such as primary pulmonary lymphoma or adenocarcinoma in situ could have an appearance similar to a focal area of COP. The diseases can be typically differentiated based on the clinical presentation and histopathologic examination. Low-grade primary pulmonary lymphoma may have some response to glucocorticoids thus mimicking COP. Adenocarcinoma-in-situ tends to have associated nodules and do not respond to glucocorticoids.

COP is associated with excellent, long-term outcomes when treated. Spontaneous remissions are seen in about 50% of mild cases. Patients demonstrate a rapid symptomatic response to treatment and up to 80% achieve complete cure. Relapses are common but do not seem to affect long-term outcomes in terms of morbidity and mortality.

Persistent pulmonary opacities with symptoms of pneumonia not improving despite antibiotic therapy should prompt suspicion for COP. Rigorous search for secondary causes should be made before diagnosing COP. Glucocorticoid therapy produces a dramatic response, and up to 80% of individuals achieve complete cure.

The diagnosis and management of COP requires an interprofessional team that includes a pulmonologist, infectious disease expert, thoracic surgeon, internist, pathologist and a radiologist. Once the diagnosis is made, the treatment is complex as there are no controlled trials comparing medications or duration of treatment in COP. Treatment regimens are based on consensus guidelines. The initial clinical presentation, severity of disease, and degree of responsiveness should be considered when deciding on an appropriate regimen and duration of therapy.

Spontaneous remissions have been described for patients with mild symptoms and minimal radiographic and PFT abnormalities. The anti-inflammatory effect of macrolides particularly clarithromycin has been exploited in some reports to treat patients with mild symptoms.

The vast majority of patients with progressive symptoms and diffuse radiographic involvement are treated with oral glucocorticoids resulting in marked improvement in symptoms. Close monitoring for adverse effects of glucocorticoids is recommended.  Patients who are unable to taper off glucocorticoids or have significant side effects to glucocorticoids can be started on a steroid-sparing agent, although COP is an unapproved indication for all steroid-sparing medications. 

COP is associated with excellent, long-term outcomes when treated. Spontaneous remissions are seen in about 50% of mild cases. Patients demonstrate a rapid symptomatic response to treatment and up to 80% achieve complete cure. Relapses are common but do not seem to affect long-term outcomes in terms of morbidity and mortality.[12]