Acute Fibrinous and Organizing Pneumonia: A Case Report and Review of the Literature

Background Acute fibrinous and organizing pneumonia is an unusual histopathological pattern of acute lung injury. To improve the understanding of acute fibrinous and organizing pneumonia, we herein present one case of a patient with acute fibrinous and organizing pneumonia proven by percutaneous lung biopsy along with clinical features, chest imaging and pathology. Case presentation A 70-year-old man was admitted to our department and was initially diagnosed to have community-acquired pneumonia. He had no specific symptoms and signs on presentation. Chest computed tomography scan showed a high-density shadow in the right basement of the lower lobe. The patient was preliminarily diagnosed with community-acquired pneumonia; however, antibacterial treatment was ineffective. To confirm the diagnosis, we performed twice percutaneous lung biopsy, and pathology was consistent with acute fibrinous and organizing pneumonia. After he was treated with glucocorticoids, the shadow seen on imaging dissipated during the follow-up period. Conclusion Acute fibrinous and organizing pneumonia is a rare histopathological diagnosis, which often has a delay in diagnosis. Clinicians need to consider the possibility of acute fibrinous and organizing pneumonia in the case of invalid antibacterial therapy. Further studies are needed to better classify acute fibrinous and organizing pneumonia, and characterise its clinical presentations, course and treatment.

The patient was preliminarily diagnosed with community-acquired pneumonia; however, antibacterial treatment was ineffective. To confirm the diagnosis, we performed twice percutaneous lung biopsy, and pathology was consistent with acute fibrinous and organizing pneumonia. After he was treated with glucocorticoids, the shadow seen on imaging dissipated during the follow-up period.
Conclusion Acute fibrinous and organizing pneumonia is a rare histopathological diagnosis, which often has a delay in diagnosis. Clinicians need to consider the possibility of acute fibrinous and organizing pneumonia in the case of invalid antibacterial therapy. Further studies are needed to better classify acute fibrinous and organizing pneumonia, and characterise its clinical presentations, course and treatment.

Background
Acute fibrinous and organizing pneumonia (AFOP) is a histological pattern associated with acute lung injury and has been referred to as a rare pathological type in recent years. After Beasley [1] first described it in 2002, AFOP cases have been increasingly reported as a rare pathological type in recent years [2][3][4]. To improve the understanding of AFOP, we herein present one case of a patient with AFOP proven by pathology, whose chest computed tomography (CT) showed remarkable improvement by glucocorticoid treatment. Our case reflects a unique clinical presentation not previously described in AFOP.

Case Presentation
A 70-year-old male, a declared nonsmoker with history of coronary heart disease, his chest CT was suggestive of alveolar consolidation in the lower right lobe because of an occasional medical examination. He had no discomfort complaints. On his admission, vital signs were within normal limits. Chest auscultation revealed breath sounds with fine crackles in the right lung. Apart from this, no other findings were remarkable. The chest CT (Fig. 1) showed patchy opacities and high density shadow in the right basement of the lower lobe. Ferritin was 395.50ng/ml. The other laboratory tests all were negative, including blood routine, liver, kidney and coagulation function tests, arterial blood gas analysis, autoimmune and tumour biomarkers, T cell spot test for tuberculosis infection, sputum culture, tubercle bacillus of sputum smears and erythrocyte sedimentation rate.
On admission, the patient was treated empirically with piperacillin-tazobactam for communityacquired pneumonia. After 10 days of treatment, chest CT scan ( To prevent recurrence, active follow-up of this patient was done to ensure that he benefit from treatment. No recurrent lesions were seen on the chest CT after 3 months.

Discussion
AFOP is a newly recognized histopathological entity of acute lung injury and has been proposed as a possible autonomic interstitial lung disease, although it is not included in the ATS/ERS classification of idiopathic interstitial pneumonias [5]. The pathological hallmark of AFOP was massive cellulose exudate with organization in the alveolar spaces, rather than the fibrous tissue and fibroblast proliferation seen in organizing pneumonia; the numerous eosinophils, macrophage infiltration and eosinophil abscesses formed in eosinophilic pneumonia; or the hyaline membranes seen in diffuse alveolar damage [6 -8 ]. It could be idiopathic or could also be associated with infection [9,10], connective tissue disease [11,12], environmental exposures to diverse agents [13], drugs reaction [14], etc ( Table 1). There was no history of connective tissue disease for AFOP in this case, with no environmental toxin exposure, chemical exposure, pets or recent travel.  [15]. In the case we have presented, the first pathology revealed cellulose exudate in a few alveolar cavity, while massive cellulose exudate with organization in the alveolar spaces in second pathology. The lung lesions seemed to be shift and migratory. This partly reflects the evolution of the subacute onset and a unique clinical presentation not previously described in AFOP. It performed similarity to cryptogenic organizing pneumonia with respect to clinical manifestations, imaging findings, treatment efficacy, and prognosis. This clinical pattern of AFOP has a less aggressive nature with slower progression.
AFOP also has nonspecific and variable radiographic appearances. The most common imaging finding is bilateral patchy infiltrates at the lung bases with ground-glass appearance and inter-lobar septal thickening [16]. Other radiographic findings reported include diffuse bilateral miliary infiltrates, as well as generalized nodules with lobar consolidation [17,18]. In addition, the images may appear similar to those in other lung diseases such as interstitial pneumonia, pulmonary edema, andinfectious pneumonia [19]. initially [20]. There is no consensus on treatment duration, and relapse may occur during the period when the dosage of steroids is reduced. One case [21] reported a long duration of steroid treatment of nearly 24 months. For subacute onset of AFOP, most are likely to have responded favorably to steroids. But an acute onset of the disease usually presents a fast progression to death due to respiratory failure and multi-organ dysfunction, which have a modest benefit with steroids and immunosuppressive therapy [17]. The dosage and duration of steroid should be individualized according to the medical course, etiology, radiological evolution and the side reaction, and more studies on treatment of AFOP are required in order to reduce the complication and improve the survival rate. Meanwhile, long-term follow-up is necessary. Attention should be paid to recurrence of the disease during hormone reduction and discontinuation.

Conclusion
In conclusion, AFOP, which is referred to as a relatively new and rare histopathology, can easily be misdiagnosed. Clinicians need to take into consideration the possibility of AFOP in the case of invalid presentations, course and treatment. This case was not novel but of significant clinical importance and very instructive.
Declarations Figure 1 Chest computed tomography scan on admission showed patchy and consolidation in the right basement lower lobe lesions (a), and the upper lobe left lung appears normal (b).   Pathological examinations revealed massive cellulose exudate with organization in the alveolar cavity, alveolar septum widened and lymphocytes and plasmocyte infiltration.

Figure 5
Chest computed tomography scan showed an increase of patchy infiltration after one month (e, f). Repeat chest computed tomography scan after one-month steroid treatment showed significant improvement, and lesions in the upper lobe of left lung almost disappeared(g, h).

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