Pathologic Aspects of Bronchiolitis Obliterans Organizing Pneumonia

Organizing pneumonia (OP) is recognized as a nonspecific lung injury response characterized histopathologically by the presence of intra-alveolar buds of granulation tissue. Most OP patients show excellent responses to corticosteroids, but relapse is frequently seen when corticosteroids are tapered or discontinued. Although several factors associated with relapse have been reported in cryptogenic OP (COP), the clinical features and risk factors associated with relapse in connective tissue disease–associated OP (CTD-OP) have yet to be fully understood.

We retrospectively reviewed data on 47 CTD-OP patients. We investigated the frequency of relapse and compared the clinical data between CTD-OP with and without relapse to clarify the risk factors for relapse.

Eleven (23.4%) CTD-OP patients had relapses of OP during the study. In the multivariate analysis, no CTD treatment at OP diagnosis [O.R. 11.920, p = 0.012] and partial remission after steroid treatment [O.R. 35.944, p = 0.045] were independent risk factors for relapse. Among rheumatoid arthritis-associated OP (RA-OP) patients, partial remission after steroid treatment [O.R. 16.151, p = 0.047] and age at OP diagnosis [O.R. 0.899, p = 0.045] were independent risk factors for relapse. Most of the relapsed OP patients who were on no medication at OP diagnosis later developed CTD.

CTD-OP patients with residual disease on HRCT after treatment and who had OP diagnosis preceding CTD diagnosis were more likely to have an OP relapse. During the clinical course of relapsed OP patients, it is necessary to pay attention to the onset of CTD.

Chronic diffuse lung diseases are dominated by a spectrum of nonneoplastic, mainly inflammatory, conditions that affect the lung parenchyma. Prominent in these conditions are the idiopathic interstitial pneumonias, pulmonary manifestations of systemic collagen vascular disease, diffuse eosinophilic lung disease, drug-associated lung disease, diffuse granulomatous lung disease, and a variety of miscellaneous diseases that remain enigmatic in terms of etiology and/or pathogenesis. Individual entities are reviewed, followed by a section highlighting a practical approach to the four most common patterns of injury encountered in practice.

Organizing pneumonia is a nonspecific pulmonary response pattern associated with a variety of clinical contexts including viral infections. The classic radiological manifestations are peribronchovascular/peripheral ground glass opacities or consolidations and may be accompanied by nodules, masses, and interstitial opacities. We describe the case of a 62-year-old male patient with SARS-CoV-2 pneumonia and torpid clinical and radiological evolution in whom organizing pneumonia was documented through transbronchial biopsy and imaging findings, with a good response to corticosteroids. The importance of recognizing the development of organizing pneumonia lies in the better prognosis and outcome in those patients who receive treatment with corticosteroids, however, the clinical and radiological suspicion must be confirmed with biopsy because radiological findings associated with bacterial coinfection may overlap.

Organizing pneumonia is characterized by a histologic pattern of plugs of granulation tissue within alveoli, alveolar ducts, and bronchioles. This nonspecific finding, in the setting of characteristic clinical and radiographic features, defines cryptogenic organizing pneumonia when no etiology is found or secondary organizing pneumonia if a cause or exposure is identified. Prognosis is usually good with the majority of patients responding rapidly to corticosteroids, though relapses are not uncommon.

This chapter is devoted to the description of morphological, clinical, and radiological features of idiopathic interstitial pneumonia (IIP). The main diagnostic features of IIP are defined, and each clinical type is described with a wide range of high-resolution computed tomography series, allowing visual comparison of closely related radiological patterns. For most common forms, descriptions of the alveoloscopic picture are provided. Differential diagnosis of IIP is often challenging, so key diagnostic points for similar diseases are discussed. Modern approaches for management of patients with IIP are also considered.

By nature, idiopathic interstitial pneumonias have been diagnosed in a multidisciplinary manner. As classifications have been subject to significant refinement over the last decade, the importance of correlating clinical, radiologic, and pathologic information to arrive at a diagnosis, which will predict prognosis in any given patient, has become increasingly recognized. In 2013, the American Thoracic Society and European Respiratory Society updated the idiopathic interstitial pneumonias classification scheme, addressing the most recent updates in the field. The purpose of this review is to highlight the correlations between radiologic and pathologic findings in idiopathic interstitial pneumonias while using updated classification schemes and naming conventions.