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Organizing Pneumonia

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ABSTRACT

Organizing pneumonia (OP) is a histologic term characterized by patchy filling of alveoli and bronchioles by loose plugs of connective tissue. OP may be an incidental finding in lung biopsy specimens or may be found nearby areas of lung involved by other diseases. On other occasions, OP may be the primary cause for pulmonary dysfunction and/or pulmonary symptoms. OP can be either idiopathic (cryptogenic organizing pneumonia, COP) or secondary to underlying disease (secondary organizing pneumonia, SOP). COP typically presents with a prodrome of symptoms of a respiratory illness followed by the insidious onset of dyspnea weeks to months later. The radiological findings typically reveal peripheral consolidation, although ground glass infiltrates or solitary nodules may be seen. The definitive diagnosis of OP requires histology. Open lung biopsy or video assisted thoracoscopy is usually required to obtain specimens large enough for the diagnosis to be made. In some cases, transbronchial biopsy specimens may be adequate for the diagnosis. The treatment of choice for OP includes corticosteroids plus treatment of the underlying disease in cases of SOP. Relapses occur frequently, usually when treatment is withdrawn or tapered. The prognosis is good in most of the cases of COP, whereas in SOP it is dependent on the underlying cause.

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Epidemiology

OP is considered to be a rare disease. A retrospective study showed that the incidence of COP was 1.10/100,000, whereas the incidence of SOP was 0.86/100,000, with an overall incidence of 1.96/100,000.2 This study also demonstrated a significant increase in the incidence of organizing pneumonias over the last 20 years. COP is not associated with race or gender.2., 3. The mean age of onset is in the fifth to sixth decade of life,4 although some cases have been reported in childhood.5 There are

Histology

The prominent histological finding in OP is patchy involvement of the pulmonary parenchyma by fibromyxoid, polypoid plugs of granulation tissue (also known as Masson bodies) within the alveoli and occasionally within the bronchioles (in which case the term bronchiolitis obliterans organizing pneumonia may be applied) (Figure 1). There is a mild interstitial infiltrate, associated with type II epithelial cell metaplasia. Foamy macrophages (macrophages that have ingested endogenous lipoid

Clinical Symptoms and Findings

The disease usually develops after a prodrome of a flu-like syndrome associated with fever, fatigue, nonproductive cough (70%), mild dyspnea (65%), and weight loss (60%), which lasts for several weeks. Radiographs typically show alveolar infiltrates (Figure 2). Antibiotic administration for a presumptive infectious pneumonia is ineffective. The diagnosis is typically not suspected for at least 4 to 10 weeks.10 Although many of the prodromal symptoms resolve, dyspnea worsens and usually becomes

Radiological Findings

There are 3 radiological patterns of OP, each associated with different clinical presentation.18., 19. The most common radiological pattern of COP is peripheral, bilateral, diffuse alveolar opacities. This pattern is often confused with infectious pneumonia. These opacities are usually located in the lower lung lobes, and they may be recurrent and migratory in up to 50% of the cases. High-resolution computed tomography (CT) detects such abnormalities in more than 90% of cases. Their density

Bronchoalveolar Lavage

The main role of bronchoalveolar lavage in the diagnosis of OP is to exclude infectious pneumonia and malignancy. There are no lavage findings that specifically confirm the diagnosis of OP.

Diagnosis

Although the typical clinical and radiological features may suggest the diagnosis of OP,25 histological confirmation is essential for the diagnosis and for the identification of causes of SOP (eg, malignancy). The location of the biopsy may be guided according to the high resolution CT findings.1

It is controversial whether transbronchial lung biopsy is adequate for the diagnosis of OP. Airspace organization or an organizing pneumonia pattern, with intraluminar buds of granulation tissue, may be

Causes of SOP

As already mentioned, Op may be either idiopathic (COP) or secondary (SOP).

Table 1 lists various etiologies for SOP. Although SOP can occur with any connective tissue disease, it is more commonly associated with dermatomyositis-polymyositis27 and rheumatoid arthritis.28 Numerous infectious pathogens are well-known causes of SOP, which usually represents an inflammatory sequela after the clearance of the infectious agent with appropriate chemotherapy.29 Interestingly, SOP can be associated with

Treatment

Spontaneous remission of organizing pneumonia is rare,12 and therefore the diagnosis of OP usually requires treatment if the patient is symptomatic. The standard treatment for OP is corticosteroids, which usually results in rapid clinical, radiological and functional improvement. However, the use of corticosteroids does not always result in complete resolution and relapses are common (see prognosis section below).6., 11. Furthermore, the numerous side effects of corticosteroids can complicate

Prognosis

The mortality of OP has been reported to vary from 5% to as high as 27%.3., 6., 7., 10., 17., 45. Mortality rates appear higher with SOP than COP.

Corticosteroid therapy results in complete recovery in up to 80% of patients within a few weeks to 3 months. The disease is persistent in the remainder.6., 7., 12., 45. The development of a reticulonodular pattern on high resolution CT is an indicator that organizing pneumonia is progressing to fibrosis.19., 46. Cases of spontaneous disease regression

Summary

Although relatively rare, OP is an important diagnosis for the clinician to consider for several reasons. First, the clinical presentation mimics pneumonia which may result in the administration of inappropriate antibiotics and a prolonged delay in diagnosis and treatment. Second, OP is associated with many specific causes (SOP) that may require therapy in order for the lung disease to be adequately treated. Third, COP is a cause of acute respiratory distress syndrome, and this would be an

References (47)

  • J.F. Cordier

    Cryptogenic organizing pneumonia

    Clin Chest Med

    (2004)
  • I.F. Purcell et al.

    Cyclophosphamide in severe steroid-resistant bronchiolitis obliterans organizing pneumonia

    Respir Med

    (1997)
  • Y.H. Lee et al.

    Dermatomyositis without elevation of creatine kinase presented as bronchiolitis obliterans organizing pneumonia

    Korean J Intern Med

    (2000)
  • K. Watanabe et al.

    Factors related to the relapse of bronchiolitis obliterans organizing pneumonia

    Chest

    (1998)
  • Am J Respir Crit Care Med

    (2002)
  • G. Gudmundsson et al.

    Epidemiology of organising pneumonia in Iceland

    Thorax

    (2006)
  • F.S. Oymak et al.

    Bronchiolitis obliterans organizing pneumonia: clinical and roentgenological features in 26 cases

    Respiration

    (2005)
  • G.R. Epler

    Bronchiolitis obliterans organizing pneumonia: definition and clinical features

    Chest

    (1992)
  • T. Inoue et al.

    Idiopathic bronchiolitis obliterans organizing pneumonia (idiopathic BOOP) in childhood

    Pediatr Pulmonol

    (1996)
  • R. Lazor et al.

    Cryptogenic organizing pneumonia: characteristics of relapses in a series of 48 patients: the Groupe d’Etudes et de Recherche sur les Maladles "Orphelines" Pulmonaires (GERM"O"P)

    Am J Respir Crit Care Med

    (2000)
  • T.E. King et al.

    Cryptogenic organizing pneumonitis: the North American experience

    Chest

    (1992)
  • T.V. Colby

    Pathologic aspects of bronchiolitis obliterans organizing pneumonia

    Chest

    (1992)
  • K. Alasaly et al.

    Cryptogenic organizing pneumonia: a report of 25 cases and a review of the literature

    Medicine (Baltimore)

    (1995)
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