Imaging findings
Case 245
【Progress】
He was given pulse spray steroid administration again but regrettably he passed away ten days after.
【Discussion】
Abrupt border between normal parenchyma and honeycomb is characteristic of usual interstitial pneumonia (UIP) (1). When exacerbation of UIP occurs, ground glass opacity and/or consolidation appears in the normal parenchyma adjacent to honeycomb pattern usually on bilateral pulmonary lower lobes, indicating the exacerbation implies volume loss of vital respiration volume. Corresponded to opacity on normal parenchyma, diffuse alveolar damage (DAD) with hyaline membrane and with/without immune cell infiltration are reported to be found on microscopic specimen (1-5). The hyaline membrane composes of surfactant, exudate from epithelial cells and fragments of catalyzed cells (2-5). DAD implies necrosis or apoptosis of type I and type II alveolar cells and fibroblast. In normal reparative response, fibroblast and myofibroblast transformed from fibroblast, type II alveolar cell and fibrocyte from bone marrow work. However, power of reparative response on exacerbation on UIP is weak and fragile because DAD indicates to damages of reparative cells. UIP is reported to arise from apoptosis of Type II(6,7). Type II alveolar cell functions like stem cell since it can transform to Type I alveolar cell and myofibroblast (6,7). Type II alveolar cells secrete surfactant and their disappearance implies fatal, poor prognosis. However, as shown in previous Case 244, steroid might be effective in case of permeability of vessel related to neutrophils infiltration because steroid leads to impede for neutrophils to go out from vessels to alveolus.
Further, Exacerbation of UIP occurs during long-term steroid administration (2-5), especially when steroid volume come to decrease for escape from steroid. At the time of steroid decrease, laboratory test reveals decrease of lymphocytes count and increase of neutrophils count. The infiltration of neutrophils to alveolus causes not only damages to alveolar cells but also permeability of vessel walls, inducing for edematous fluids to fill in alveolar space and leading to ARDS (acute respiratory distress syndrome). In our case, he was given steroid therapy for past four months. UIP exacerbation occurred during the time of decreasing steroid with lymphocyte 570/mm3(8). It is reported that the count of lymphocyte 650 or less causes ARDS(8). In clinical reality, re-increase of steroid administration was reluctant but was conducted in our case, but in vain leading poor prognosis.
Honeycomb pattern on MRI is usually found in marginal areas of bilateral lower lobes, extending along with pleura and interlobular fissure. These peripheral alveoli spaces are anatomically more expanding than the proximal alveoli spaces. Surfactant plays a crucial role of preserving homogeneous pressure in alveolar spaces irrespective of large or narrow alveolar space. In short, surfactant is contained much more in proximal alveolus than in peripheral alveolus for smooth alveolus expansion and decrease. It implies more Type II alveolar cells in proximal alveolus than in peripheral alveolus because they secrete surfactant. When surfactant is deficient in some alveoli, they are susceptible to surface pressure increase. The increased surface pressure of alveolar spaces with least surfactant dilated when expiration and stable or preserving dilatation when inhalation. The ability of surfactant to lower surface tension is proportional to its concentration within the alveolus. The surfactant volume is probably proportional to the number of alveolar cell type II. The peripheral alveolus includes less number of alveolar cell type II than the proximal alveolus. If UIP arises from apoptosis of type II alveolar cell, UIP figure, honeycomb pattern might occur first on the area with less number of type II alveolar cell. In our case, UIP with honeycomb pattern was found in the peripheral area of bilateral lower lobes.
【Summary】
We presented an eighty five-year-old male with interstitial pulmonary fibrosis, suffering from breathing disorder. CT showed honeycomb pattern plus consolidation in the normal parenchyma adjacent to honeycomb area. He was given long-term steroid. However, exacerbation of UIP occurred during the trial of escaping steroid, decreasing steroid volume. Regrettably, he passed away twenty days. It is borne in mind that UIP exacerbation occurs at the right time of steroid decrease for escape after long-time administration of steroid. Opacity of normal parenchyma adjacent to honeycomb pattern is composed of diffuse alveolar damage (DAD) with hyaline membrane and with or without immune cells infiltration. If DAD with immune cells infiltration is found microscopically, steroid might be effective but if not, steroid will not. The reason why honeycomb pattern is found in margin areas in bilateral lower lobes, might be related to the number of type II cells that secrete surfactant because UIP arises from apoptosis of type II cell and type II cells exist less in peripheral area than in proximal area.
【References】
1.Citation: Souza CA, et al. Idiopathic Pulmonary Fibrosis: Spectrum of High-Resolution CT Findings. American Journal of Roentgenology. 2005;185: 1531-1539.
2.Azadeh N, Moua T, Baqir M, Ryu JH. Treatment of acute exacerbations of interstitial lung disease. (2018) Expert review of respiratory medicine. 2018; 12 (4): 309-313.
3.Kolb M, et al. Acute exacerbations of progressive-fibrosing interstitial lung diseases. (2018) European respiratory review : an official journal of the European Respiratory. Society. doi:10.1183/16000617.0071-2018 - Pubmed
4.Luppi F, et al. Acute exacerbation of idiopathic pulmonary fibrosis: a clinical review. Internal and emergency medicine. 2015; 10 : 401-11.
5.Marchioni A, et al. Acute exacerbation of idiopathic pulmonary fibrosis: lessons learned from acute respiratory distress syndrome? Critical Care 2018;22, Article no. 80
6.Elena Lopez-Rodriguez E, et al. Lung surfactant metabolism: early in life, early in disease and target in cell therapy. Cell Tissue Res 2017;367:721-735
7.Leanne M, et al. Alveolar type II cell apoptosis. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 2001; 129:267-285
8.Kojima K , et al. Clinical Characteristics and Risk Factors for Pneumocystis Jirovecii Pneumonia during Immunosuppressive Treatment in Patients with Ulcerative Colitis: A Retrospective Study. J Gastrointestin Liver Dis 2020;29(2):167-173
2021.10.1