Review
Criteria for the diagnosis of idiopathic pleuroparenchymal fibroelastosis: A proposal

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Abstract

Background

Physicians have few opportunities to perform surgical lung biopsy (SLB) to diagnose idiopathic pleuroparenchymal fibroelastosis (IPPFE). Therefore, diagnostic criteria for IPPFE that do not require SLB must be established. Herein, we propose diagnostic criteria for IPPFE with and without SLB.

Methods and results

The diagnostic criteria for IPPFE with SLB are histological, based on computed tomography (CT) lesions compatible with PPFE, predominantly in the upper lobes. The three diagnostic criteria for IPPFE without SLB are as follows: (1) radiologically possible IPPFE (a radiological criterion confirming CT lesions in both lung apexes, regardless of the lower lobe lesions); (2) radiologically probable IPPFE (also a radiological criterion, but mandatory to confirm chest radiograph findings of bilateral upward shift of the hilar structures and/or CT findings of volume loss of the upper lobes); (3) radiologically and physiologically probable IPPFE. Our data from 41 patients with IPPFE and 97 with idiopathic pulmonary fibrosis (IPF) showed that the percentage of the predicted values of the ratio of residual volume to total lung capacity (RV/TLC %pred.) ≥115% and body mass index (BMI) ≤20 kg/m2 plus RV/TLC %pred. ≥80% performed well for discriminating IPPFE from IPF. These parameters were thus added to criterion (3).

Conclusions

We have proposed diagnostic criteria for IPPFE in patients with and without SLB. Both imaging criteria and physiological criteria using RV/TLC and BMI successfully discriminate IPPFE from chronic IIPs when SLB cannot be performed.

Introduction

In 1992, Amitani et al. published a case series of 13 patients with a peculiar pulmonary fibrosis of unknown etiology that was localized in the bilateral upper lobes [1]. Based on imaging pattern characteristics, they named the fibrotic disease idiopathic pulmonary upper lobe fibrosis (IPUF). In the same paper, they presented 10 clinical, imaging, and histological characteristics of the condition: (1) constitutional slender stature with flattened thoracic cage; (2) chest radiograph findings of bilateral progressive fibrosis of the upper pulmonary lobes, with upward hilar retraction and volume loss in the upper lobes, but with few or no fibrotic opacities in the middle and lower lobes; (3) lesions in the subpleural areas with an apical cap-like appearance on chest radiograph; (4) appearance of multiple cysts in the lesions as the disease progresses, but without honeycombing; (5) frequent complication of recurrent and bilateral pneumothorax; (6) absence of extrathoracic lesions; (7) absence of acid-fast bacilli and no therapeutic effect of antituberculous drugs; (8) possible superimposed aspergillus infection; (9) slowly progressive condition and ultimately death within 10–20 years of presentation; (10) histological findings of non-specific fibrosis in the subpleural areas.

The Amitani et al. paper inspired Japanese investigators to publish several reports on IPUF itself [2], [3], [4], [5], [6], as well as on idiopathic upper lobe-dominant pulmonary fibrosis [7], [8], which is closely related to IPUF. In 2004, Frankel et al. described five patients with pulmonary fibrosis of unknown etiology. The patients predominantly showed bilateral involvement of the upper lobes, with pleural thickening. The investigators named the disorder idiopathic pleuroparenchymal fibroelastosis (IPPFE) after its histopathological characteristics, which differed from those of all previously described idiopathic interstitial pneumonias (IIPs) [9]. IPPFE, IPUF, and idiopathic upper-lobe-dominant pulmonary fibrosis overlap in terms of both histopathology and clinical features, but IPPFE is currently categorized by the American Thoracic Society and European Respiratory Society as a rare IIP [10]. Therefore, in the present paper, we have included both IPUF and idiopathic upper-lobe-dominant pulmonary fibrosis in the definition of IPPFE [11].

With this in mind, we propose diagnostic criteria for IPPFE in patients who have undergone surgical lung biopsy (SLB) and those who have not (Table 1, Table 2, Table 3, Table 4, Table 5). In practice, clinicians have limited opportunities to perform SLB in patients with suspected PPFE because such patients tend to have poor physiological and/or general condition, as well as an increased risk of postoperative complications liked prolonged pneumothorax [12]. Thus, researchers and clinicians must establish clinical diagnostic criteria for IPPFE in the absence of SLB.

The Medical Ethics Review Board of Fukuoka University approved the present study (#2018M70).

Section snippets

Diagnostic criteria for IPPFE in patients with SLB (Table 1)

We propose the following three criteria for the diagnosis of “definite IPPFE” in patients who have undergone SLB: (1) Multiple subpleural areas of airspace consolidation, with traction bronchiectasis located predominantly in the upper lobes, as visualized on high-resolution computed tomography (HRCT) scans (Fig. 1) [10], [13], [14], [15], [16]. (2) SLB findings of subpleural zonal or wedge-shaped dense fibrosis consisting of collapsed alveoli and collagen-filled alveoli with alveolar septal

Discussion

In the present manuscript, we have proposed diagnostic criteria for IPPFE both with and without SLB. IPPFE is not as rare as was previously considered [52]. However, clinicians still lack universally accepted criteria to diagnose the condition. Such criteria are urgently needed, especially in the case of patients from whom it is impossible to obtain biopsy samples.

Previous therapeutic trials involving IPPFE have all been single-center studies reporting either a single case or a small sample of

Conclusion

We have proposed criteria for the diagnosis of IPPFE with and without SLB. Because physicians have few opportunities to perform SLB in suspected IPPFE, criteria for the diagnosis of IPPFE that do not require SLB must be established. Physiological criteria, RV/TLC %pred. ≥115% and/or BMI ≤20 kg/m2 plus RV/TLC %pred. ≥80%, may successfully discriminate patients with IPPFE from those with chronic IIPs.

Role of the funding source

This study was partially supported by a grant from the Ministry of Health, Labour and Welfare of Japan, awarded to the Study Group on Diffuse Pulmonary Disorders, Scientific Research/Research on Intractable Diseases.

Conflicts of interest

The authors have no conflicts of interest for this article.

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