Clinical Characteristics and Treatment of Acute Fibrinous and Organizing Pneumonia: Two Case Reports and Literature Review

Background Acute brinous and organizing pneumonia (AFOP) is a rare histologic interstitial pneumonia pattern characterized by the intra-alveolar brin deposition and organizing pneumonia. Though a small amount of cases has been reported, its causes and clinical characteristics are still not well known and there is no standard treatment yet. Case presentation We report two cases with a histological diagnosis of AFOP. Case 1 was idiopathic AFOP and presented with fever, dyspnea, cough, while the case 2 was associated with SLE and fever was her most common symptom. Their chest CT scan revealed bilateral multiple consolidations, predominantly in the lower lobes. Both cases were diagnosed after a second lung biopsy and treated with corticosteroids. Conclusions We not only describe two rare AFOP cases but also demonstrate the most comprehensive review to date in AFOP, including 150 patients since 2002. Most common symptoms include dyspnea, cough, and fever. Consolidation was the most common imaging pattern, followed by GGO and nodules. Given the various etiology and nonspecic clinical presentation, AFOP probably had been under diagnosed. Early identication is very important for AFOP management and a lung biopsy is required for a denitive diagnosis. Corticosteroids was recommended to be the most useful therapy, and treatment options should depend on the etiology and disease severity.


Introduction
Acute brinous and organizing pneumonia (AFOP) is a rare histologic interstitial pneumonia pattern characterized by the intra-alveolar brin deposition and organizing pneumonia. Since the rst description of the disease in 2002 by Beasley [1], a small amount of cases has been reported, but its causes and clinical features are still not well known. Moreover, there is no standard treatment yet. Clinical outcomes also vary due to its diversity, but most cases have been associated with poor prognosis.
Here we present the whole clinical course in two cases with a histological diagnosis of AFOP at a tertiary hospital in China. Furthermore, we described the most comprehensive literate review of the AFOP to identify the clinical characteristics and management, in order to provide clinicians with better understanding of this disease.
Case Presentation Case 1 On initial physical examination she had anemic appearance and moist rales could be heard on both lungs. Laboratory data showed normal white blood cell count with decreased hemoglobin count (75 g/L), while platelet was slightly elevated (315 ×10^9/L). Serum CRP and ESR were both elevated. Serum PCT, 1-3-β-D Glucan and Galactomannan measurement, T-SPOT and the puri ed protein derivative test were normal. Blood and sputum cultures were negative as well as in uenza A and B, pneumococcal antigen, and Mycoplasma pneumoniae IgG and IgM. Tumor markers and serological investigations for connective tissue disease such as SLE, rheumatoid arthritis and vasculitis were all negative. Bronchoscopy was performed and the bronchoalveolar lavage (BAL) culture showed no organisms. Pathology of transbronchial lung biopsy of left lateral basal segment revealed the lung tissue structure is generally preserved, with thickened alveolar walls, brous tissue proliferation, accompanied by in ammatory cell in ltration, a large amount of red-stained cellulose-like material exuded from the alveolar cavity, suggesting the possibility of interstitial pneumonia.
On day 6 th of admission to our hospital, the patient had fever and chills again, with the highest temperature of 38.5 ℃. She was treated by intravenous moxifoxacin for 7 days. Then the antibiotic was escalated to imipenem-cilastatin, but she still had intermittent fever and developed tachypnea. On day 18 th of admission, the chest CT was reviewed which showed bilateral pulmonary lesions were advanced (Fig. 1B). Subsequently, percutaneous lung biopsy under the guidance of ultrasound was performed and histological examination demonstrated a large amount of brin exudate was seen in the alveolar lumen, the alveolar spacing was signi cantly widened, accompanied by a large number of lymphocytes, plasma cells and a small number of neutrophils, and focal broblast proliferation formation of organizing foci (Fig 2). Base on clinical, considered the possibility of AFOP. Special stains for fungi and mycobacterium tuberculosis infection were negative. These histologic ndings were mostly consistent with AFOP.
Intravenous corticosteroid (methylprednisolone, 80 mg/day for 3 days, followed by 60 mg/d for 1 week and 40 mg/day for another 1 week) was administered. Her clinical symptoms improved and fever did not recurred. At the 12 th day of the steroid treatment, opacity in both lungs decreased (Fig. 1C). The patient discharged on a regular tapering schedule of methylprednisolone. One month after hospital discharge, the chest CT showed decreased bilateral consolidation. At 3 rd month (Fig. 1D) and 6th month follow-up, her clinical condition was stable, but relapse occurred and CT showed new lesion in the upper lobe of the left lung when the dose was reduced to 12mg around 9-month after discharge. She got improvement again after re-prescribed by methylprednisolone of 40 mg/day. The patient was still being follow-up and on another regular and slower tapering of corticosteroids.

Case 2
A 54-year-old non-smoking woman was admitted because of fever for 3 days in April 5, 2017. She had a history of SLE with secondary hematological lesion and had been treated with methylprednisolone and cyclophosphamide for 13 years. She also complained of recurrent joint pain, rash, fatigue during the past 15 months. The patient had no history of substance abuse or occupational exposure.
Physical examination on admission showed moderate anemia appearance, dark red nodular rash on both lower extremities, no edema and no rales heard in both lungs. Blood routine examination revealed a white blood cell count of 10.58*10^9/L with neutrophil pre-dominance (90.1%), hemoglobin 72.0 g/L, and reticulocytes% 2.41%. Anti-cardiolipin antibody, ANA and SSA were positive while other serum examination for autoimmune disease including ANCA, RF and Coombs test were all negative. Other serological investigations showed normal procalcitonin, increased C-reactive protein, lactate dehydrogenase and D-dimer, positive T-SPOT and aspergillus galactomannan measurement, negative human immunode ciency virus, EB virus, CMV-DNA, Mycoplasma pneumoniae antibody, 1-3-β-D Glucan measurement, Cryptococcus neoformant antigen and tumor markers. The blood cultures revealed no bacteria growth. Chest CT revealed multiple nodules, consolidations and pacthy opacities in both lungs, predominantly in the lower lobes, with mediastinal lymph nodes slightly enlarged (Fig. 3A). The lesions were mostly subpleural. During hospitalization, she had been diagnosed with myelodysplastic syndrome (MDS) by bone marrow smear and biopsy.
Moxifoxacin was initiated for anti-infection from the rst day of admission and switched to meropenem and linezolid on day 6th. Medrol 20mg/d was used to treat SLE. Empirical antituberculous and antifungal therapy were added on days 3 and 5, respectively. In spite of the treatment, the patient had recurrent high fever with temperature up to 40.5 ℃. On day 6th of admission, the patient underwent bronchoscopy and transbronchial lung biopsy. The pathology demonstrated a little bronchial mucosa and cellulolytic exudate, without any evidence of cancer. Fungal stainings were all negative. Culture of BALF, smear microscopy for acid-fast bacilli, and aspergillus antigens were all negative.
Two weeks after admission, chest CT indicated an increase of nodules and consolidations in both lungs and a small amount of bilateral pleural effusion (Fig. 3B). Ultrasound-guided percutaneous lung biopsy was performed and the pathology revealed that the lung tissue was lled with brous exudate and the alveolar walls were in ltrated with large amount of lymphocytes, with interstitial brosis (Fig 4). Special stain (Grocott methenamine silver) for fungal infection was negative.
These ndings were mostly consistent with AFOP. High dose of intravenous methylprednisolone (320mg/d for 1 day and 200mg/d for another 2 days, followed by 80 mg/day for 1 week) was administered intravenously, resulting in improvement of clinical symptoms and chest radiography ndings (Fig. 3C), which showed absorption of bilateral lung lesions at day 7 of the steroid treatment.
However, the patient had fever recurrent after the methylprednisolone tapered to 40mg/d in the 11th day of corticosteroid treatment and chest CT showed the lesions were signi cantly more advanced than before. The patient's symptoms showed no improvement when the dosage of methylprednisolone was added to 160mg/d. Then the treatment was adjusted to intravenous dexamethasone 30mg/d for 5 days (followed by methylprednisolone 40mg bid), combined with intravenous cyclophosphamide (0.2 QOD for 3 times). The patient's temperature returned to normal ve days later.

Discussion And Conclusion
AFOP is a histopathologic diagnosis that was rst reported in 2002 by Beasley et al. in a case series involving 17 patients with acute respiratory failure [1] and was de ned as a subgroup of idiopathic interstitial lung disease [2] in 2013 in the American Thoracic Society/European Respiratory Society statement. The pathology characterized by brin deposition in pulmonary alveoli and organization of loose connective tissue. The other characteristic feature is the absence of Classical hyaline membranes of diffuse alveolar damage and no eosinophil in ltration or granuloma formation. The etiology of AFOP can either be idiopathic or associated with a wide range of medical conditions or risk factors, such as lung transplantation, cancer, medication reaction and so on. In the literature review, 50 cases had no underlying cause or association, diagnosed as idiopathic AFOP, while the other 100 cases were identi ed as secondary AFOP (Table 2). In addition, 17 (11.3%) patients had no signi cant medical history and were apparently healthy prior to the present illness (Table 2). It should be noted that there were two cases caused by immune checkpoint inhibitor (ICI) (Nivorumab and pembrolizumab, respectively for speci c) [8,21], which is one of the most popular and effective treatments for metastatic melanoma and advanced non-small cell lung cancer in recent years. AFOP should be taken into account when considering ICI-related pneumonitis for PD1/PD-L1 inhibitors. Smoking appeared not to be a risk factor for only 22(38%) had a history of smoking, of the 58 patients with available data. The smoking ratio seemed to be higher in the secondary-AFOP populations than in the idiopathic-AFOP group, with 47%( 14/30) to 29%(8/28).
Clinical manifestations of AFOP appeared to be nonspeci c. Most common symptoms reported included dyspnea in 108 (72%), cough in 106 (71%) (87 had a non-productive cough), fever in 64(43%), and chest pain in 24 (16%) ( Table 1). Other less common symptoms included hemoptysis, fatigue, chills, night sweat and weight loss. One patient was asymptomatic. Fever was considered to be more common in AFOP when compared with other forms of interstitial pneumonia [27]. The disease progression was acute in 41 patients, subacute in 62 patients, while the remaining were unspeci c.
Most patients underwent chest CT scan, except 2 patients with acute process only had X-rays and radiologic images were not speci ed in 3 cases. The most common CT ndings were bilateral patchy in ltrate and diffuse consolidation, often with basal or peripheral distribution. One hundred and sixteen patients presented a bilateral distribution, while 18 cases were limited to unilateral lung (the ratio of right to left was 2 to 1). Lung lesion was localized or greater in lower lobes in 29 cases, while 11cases reported mainly in the upper lobes. The most common imaging pattern was consolidation in 79 patients, of which there were 28 cases together with ground-glass opacity GGO ; GGO in 61 patients and nodules in 29 cases (Table 1). Compared with patients of secondary-AFOP, patients of idiopathic -AFOP showed more imaging nding with consolidation and less proportion with GGO. Air bronchogram was often reported with consolidation. Other less common radiographic ndings included traction bronchiectasis, mild or medium hilar and mediastinal adenopathy and halo sign. Pleural involvement seemed not to be common presentation, for only 7 cases were with mild bilateral effusion, 3 with slight right pleural effusion and only 2 patients had pneumothorax. In addition, the images present as interstitial pneumonia in 11 cases and showed the lesion as a solitary mass suggestive of a primary lung tumor in 2 cases. All of these atypical images were seen in the Secondary-AFOP.
The nonspeci c clinical features result in misdiagnosis and a delay in the diagnosis of AFOP. At the time of initial diagnosis, most cases were misdiagnosed as lung infection, while a few cases were misdiagnosed as lung cancer. Of the cases caused by non-infectious factors, 81 cases were empirically treated with antibiotics, the vast majority with broad-spectrum antibiotics and some with antifungal therapy, when 60 cases were not speci c. Beasley and his colleagues[1] described a mean time from onset of symptoms to diagnosis of 19 days, and Gomes et al [4] reported a mean time of 43.9 days.
A lung biopsy is required for a de nitive diagnosis of AFOP, including examinations for microbiology to exclude infections. The lung lesion tissue was procured by surgical lung biopsy (mainly by video-assisted thoracic surgery, VATS) in 60 patients, transbronchial lung biopsy in 43 patients, image-guided (CT-or ultrasound-guided) percutaneous lung biopsy in 31 patients, autopsy in 13 patients and unspeci ed lung biopsy techniques in 3 patients. Of the cases reviewed, 28 patients underwent BAL before pathological diagnosis and no conclusive ndings were found. Both of our cases' BAL culture and transbronchial biopsy were inconclusive and the diagnosis was con rmed by percutaneous lung biopsy. It is best diagnosed with open-lung biopsy (or video-assisted thoracic surgery biopsy), given the risk of missing areas of hyaline membranes of diffuse alveolar damage. However, we suggest that the method of lung biopsy should be based on the actual clinical situation, including the location of lung lesions and the patient's tolerance to the operations. The differential diagnosis should include bronchiolitis obliterans organizing pneumonia, eosinophil pneumonia, and diffuse alveolar damage.
Regarding therapy for AFOP, there are still no standard treatment recommendations. The most common therapy in the literature for AFOP was corticosteroids, with 132 out of 150 patients( 88%). There is no consensus on the dose and duration of corticosteroids and the therapy should be individualized, according to the etiology, clinical course and response. The initial dosage of steroids was reported in 55 cases, varying from prednisone 0.5 mg/kg/day (or equivalent) to methylprednisolone 1000 mg/day, with 28 (51%) cases of prednisone 0.5-1.5 mg/kg/day. A pulse therapy of corticosteroids (prednisone 500mg/day to methylprednisolone 1000mg/day) was administered in 12 cases. Relapse may occur during steroid tapers and symptoms mostly could relieve again when higher doses were resumed. In our two cases, steroid was prescribed as soon as the diagnosis was established and relapse happened when steroid reduced.
Other drugs reported in the literature were antibiotics (especially for those caused by infection), immunosuppresants, etanercept, indomethacin and immunoglobulin, with varying results. Immunosuppressive agents such as cyclophosphamide, mycophenolate mofetil, cyclosporine, azathioprine, tacrolimus and so on, had been tried in 17 patients, all combined with corticosteroids.
Patients secondary to autoimmune diseases may bene t most from immunosuppressant combined with steroids. GL Simmons et al [25] reported the rst case AFOP after HSCT in 2016 successfully treated with etanercept, a TNF inhibitor, and Zhou et al reported that low dose indomethacin combined with methylprednisolone was a new choice of treatment for AFOP after a surgical resection of rectal adenocarcinoma [28]. AFOP associated of anti-EJ autoantibodies with necrotizing myopathy was recently reported with good response to intravenous methylprednisolone and immunoglobulin [23].
Other therapeutic interventions included drug discontinuation, surgical resection, and organ transplantation. For patients suspected to be caused by drugs or environmental/occupational exposures, withdrawal is the most fundamental treatment. In 13 cases caused by a medication, treatment with corticosteroids and discontinuation of the drug mostly resulted in improvement and resolve, except 2 patients died even though they were treated combined with immunosuppressive agents and 2 cases died of other complication. Lung resection was reported as a successful cure while the disease is relatively localized, by Santos C et al from Portugal [29]. Labarinas S et al described a case of AFOP associated with hepatic failure and very severe aplastic anemia, responding to immunosuppressive therapy and hematopoietic stem cell transplantation [30]. There was one report of bilateral lung re-transplantation with subsequent improvement of symptoms in a patient suffering AFOP after lung transplantation [31] and lung transplantation was also reported last year by Alessio Campisi (Italy) as a successful cure in two cases of idiopathic AFOP [6]. Though AFOP has been described following organ transplantation, organ transplantation may be indicated to treat AFOP refractory to medical treatment [6,30,31]. However, further studies are required to nd out whether these kind of patients will undergo recurrence of AFOP.

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The prognosis of AFOP appears to have two different clinical patterns: one is an acute onset with a fast progression, more likely leading to respiratory failure and death, and the other is a subacute form associated with a less fulminating course and a more favorable outcome. Among the 150 case reports, 59 (39%) patients died (10 were unrelated to AFOP) ( Table 1). Of those 49 cases died of AFOP , the progression was acute in 17 81% cases while 28 cases were not speci ed. Median time between onset of symptom to death of 22 AFOP patients after lung transplantation reported by Paraskeva et al was 101 days [26]. AFOP after lung transplantation seemed to have relatively poor prognosis with poor response to drugs [26]. Patients with acute presentation or secondary-AFOP had higher mortality rate than their corresponding cases. This might due to the secondary-cases with more or worse underlying diseases and lower responsive rate to corticosteroid. Additionally, we found that the development of dyspnea and GGO on CT scan as well as lack of consolidation in AFOP seemed to be associated with poor prognosis. However, ndings from the present study require further evaluation.
In conclusion, this is the largest review to date dealing with AFOP, which includes 150 patients of AFOP, reported over an 18-year period. Given the various etiology, nonspeci c clinical presentation and insu cient understanding of pathology, AFOP probably had been under diagnosed or misdiagnosis. Our two cases highlight the importance of being aware of this uncommon pattern of acute lung injury. AFOP should be considered when encountering a suspected pulmonary infection case unresponsive to empirical antibiotic therapy, especially with bilateral, basilar or peripheral-predominant consolidation, with or without GGO or nodular in ltration on CT scan. We highly suggest appropriate lung biopsy and thorough pathologic evaluation for these patients, to establish the diagnosis and to improve the outcome by administering more aggressive therapy. Corticosteroids was recommended to be the most useful therapy currently, and treatment options should depend on the etiology and disease severity. Values are mean ± SD or n (%).
* not including all the cases for some were not reported.
AFOP=Acute brinous organizing pneumonia, GGO= Ground-glass opacity   Histologic ndings of case 1 on lung biopsy. (A) hematoxylin and eosin stain, ×100; (B) hematoxylin and eosin stain, ×200. Alveoli were lled with brin exudate without pulmonary hyaline membrane, the alveolar septum was thickened and in ltrated with a few of in ammatory cells, which were consistent with AFOP.