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We thank A. Raja and colleagues for their interest in our article on risk factors for fibrotic-like changes after severe COVID-19 infection (1). We agree that identification and management of post-COVID fibrosis continues to be impeded by the lack of consensus definitions and we look forward to further studies that help describe the natural history of post-COVID pulmonary manifestations.
The authors propose that lung fibrosis be classified into different ILDs by the pattern of lung parenchymal abnormalities six months after the initial COVID illness has resolved. We agree with the authors that persistent radiographic abnormalities are an adverse outcome of COVID that deserve future study, but we disagree with their proposed classification of patterns. We believe that recognition of fibrotic interstitial lung abnormalities (ILAs), as opposed to non-fibrotic ILAs, help prognosticate which abnormalities are less likely to resolve over time (2). Han et al (3) recently demonstrated that individuals with post-COVID fibrotic ILAs at six months had persistent fibrosis at 1-year, suggesting that fibrotic ILAs rarely resolve completely. Ultimately, serial imaging, quantitative measures of fibrosis (4), and assessment of pharmaceutical interventions (5), will be key to fully understanding the trajectory of post-COVID fibrosis.
Secondly, the authors report that disease severity did not significantly impact the development of particular parenchymal abnormalities on CT...
Secondly, the authors report that disease severity did not significantly impact the development of particular parenchymal abnormalities on CT scan. The authors do not provide analyses in their study to support this statement. Their cohort was sampled from survivors with a persistent need for oxygen therapy, was not sampled randomly from the larger acute COVID population, and only included two subjects who required invasive mechanical ventilation. While we agree that an interplay of many factors contribute to pattern and extent of parenchymal lung disease, we believe that greater severity of illness, as determined by need for invasive mechanical ventilation, should be recognized as a risk factor for persistent fibrotic abnormalities. This conclusion is supported by our study as well as others (1, 6, 7).
Claire McGroder, MD
Mary Salvatore, MD
Eric A. Hoffman, PhD
Matthew Baldwin, MD
Christine Kim Garcia, MD, PhD
1. McGroder CF, Zhang D, Choudhury MA, Salvatore MM, D'Souza BM, Hoffman EA, Wei Y, Baldwin MR, Garcia CK. Pulmonary fibrosis 4 months after COVID-19 is associated with severity of illness and blood leucocyte telomere length. Thorax 2021.
2. Putman RK, Gudmundsson G, Axelsson GT, Hida T, Honda O, Araki T, Yanagawa M, Nishino M, Miller ER, Eiriksdottir G, Gudmundsson EF, Tomiyama N, Honda H, Rosas IO, Washko GR, Cho MH, Schwartz DA, Gudnason V, Hatabu H, Hunninghake GM. Imaging Patterns Are Associated with Interstitial Lung Abnormality Progression and Mortality. Am J Respir Crit Care Med 2019; 200: 175-183.
3. Han X, Fan Y, Alwalid O, Zhang X, Jia X, Zheng Y, Shi H. Fibrotic Interstitial Lung Abnormalities at 1-year Follow-up CT after Severe COVID-19. Radiology 2021; 301: E438-E440.
4. Nagpal P, Motahari A, Gerard SE, Guo J, Reinhardt JM, Comellas AP, Hoffman EA, Kaczka DW. Case Studies in Physiology: Temporal Variations of the Lung Parenchyma and Vasculature in Asymptomatic COVID-19 Pneumonia: A Multi-Spectral CT Assessment. J Appl Physiol (1985) 2021.
5. Myall KJ, Mukherjee B, Castanheira AM, Lam JL, Benedetti G, Mak SM, Preston R, Thillai M, Dewar A, Molyneaux PL, West AG. Persistent Post-COVID-19 Inflammatory Interstitial Lung Disease: An Observational Study of Corticosteroid Treatment. Ann Am Thorac Soc 2021.
6. Francone M, Iafrate F, Masci GM, Coco S, Cilia F, Manganaro L, Panebianco V, Andreoli C, Colaiacomo MC, Zingaropoli MA, Ciardi MR, Mastroianni CM, Pugliese F, Alessandri F, Turriziani O, Ricci P, Catalano C. Chest CT score in COVID-19 patients: correlation with disease severity and short-term prognosis. Eur Radiol 2020; 30: 6808-6817.
7. Han X, Fan Y, Alwalid O, Li N, Jia X, Yuan M, Li Y, Cao Y, Gu J, Wu H, Shi H. Six-month Follow-up Chest CT Findings after Severe COVID-19 Pneumonia. Radiology 2021; 299: E177-E186.
We read with interest McGroder et al’s study on the radiographic findings of patients four months after severe COVID-19 and the associated risk factors. Hürsoy and colleagues’ comment (1) on the paper was equally thought-provoking. We would like to further this discussion by contributing some of our observations from the pulmonology clinic at a major academic medical center in South East Asia.
It has been tremendously challenging globally to achieve precision in the diagnosis of Interstitial Lung Disease (ILD) post-COVID as invasive testing such as lung biopsies are performed sparingly. Histopathological pulmonary findings have largely remained inaccessible since COVID survivors are hypoxic so biopsies pose a high risk for the patient, and healthcare personnels are reluctant to perform such high-risk procedures. Hence, we are left to derive our diagnosis from radiological data and pulmonary function tests (PFTs) of the patient.
We propose that a consensus definition be reached for the diagnosis of post-COVID ILD, one that incorporates well-accepted radiological terms (used to represent any interstitial lung disease). We recommend that lung fibrosis only be classified as ILD if the lung parenchymal abnormalities persist for a minimum of six months after the COVID infection has resolved. Post-COVID ILD should then be further subclassified based on distinct radiological patterns. In our retrospective cohort study, four patterns of post-COV...
We propose that a consensus definition be reached for the diagnosis of post-COVID ILD, one that incorporates well-accepted radiological terms (used to represent any interstitial lung disease). We recommend that lung fibrosis only be classified as ILD if the lung parenchymal abnormalities persist for a minimum of six months after the COVID infection has resolved. Post-COVID ILD should then be further subclassified based on distinct radiological patterns. In our retrospective cohort study, four patterns of post-COVID lung parenchymal changes were exhibited by patients with no preexisting lung disease: persistent ground-glass opacities; interlobular septal thickening; reticulation and honeycombing; interlobular septal thickening and reticulations; and patchy consolidation with or without ground-glass opacity (2).
In terms of outcome, within our cohort of severe to critically ill patients, most developed persistent ground-glass opacities or patchy consolidation (with or without ground-glass opacity); a majority of these participants significantly improved (clinically and radiologically) upon administration of corticosteroids (2). Radiological improvement was defined as clearance of at least 50% of lung infiltrates. Reiterating our findings, Han et al. reported ground-glass opacities as the predominant pattern observed in follow-up CT scans of patients with fibrotic-like changes within six months of disease onset (3). Three of the five patients in our study who died had progressive disease with reticulation and honeycombing. To achieve greater accuracy in disease severity assessment and risk stratification, we suggest employing PFTs, particularly to obtain diffusion capacity of the lungs for carbon monoxide (DLCO) and forced vital capacity (FVC) measurements. For the eight out of thirty patients in our cohort who had significant HRCT findings, PFTs were ordered to assess physiological function; three presented with low FVCs (2). In Han et al’s study, abnormal DLCO (less than 80%) at 6-month follow up was a common occurrence in those with fibrotic-like changes (3).
Similar to McGroder et al’s findings, we concluded that the male gender was a significant predisposing factor for post-COVID pulmonary fibrosis. Moreover, like Li et al. and Han et al., we found diabetes mellitus and hypertension to be prevalent comorbidities in patients who developed fibrotic changes (2-4). Interestingly, in our cohort, disease severity did not significantly influence the development of any particular pattern of lung parenchymal abnormality. In light of these observations, we can conclude that the reported lung microstructure changes are not only a ramification of post-ARDS fibrosis or ventilator-induced lung damage but also a consequence of direct virus attack and aberrant local immune response. This is further evidenced by the finding that the Coronavirus induced fibrosis even in moderately ill patients who did not require invasive mechanical ventilation or ICU stay (2).
We hope that prospective studies will further enrich and broaden the global dialogue on post-COVID lung fibrosis.
1. Hürsoy et al. 2021. e-letter https://thorax.bmj.com/eletters
2. Zubairi ABS, Shaikh A, Zubair SM, Ali AS, Awan S, Irfan M. Persistence of post-COVID lung parenchymal abnormalities during the three-month follow-up. Adv Respir Med. 2021;89(5):477–83. Available from: https://pubmed.ncbi.nlm.nih.gov/34612504/
3. Han X, Fan Y, Alwalid O, Li N, Jia X, Yuan M, et al. Six-month Follow-up Chest CT Findings after Severe COVID-19 Pneumonia. Radiology. 2021;299(1):E177-E186.
4. Li Y, Wu J, Wang S, Li X, Zhou J, Huang B, et al. Progression to fibrosing diffuse alveolar damage in a series of 30 minimally invasive autopsies with COVID-19 pneumonia in Wuhan, China. Histopathology. 2021;78(4):542-55.
To the editor,
We thank N. Hürsoy and colleagues for their interest in our study of patients four months after severe COVID-19 . We agree that there needs to be continued development of terms describing the radiographic appearance of post-COVID fibrotic-like patterns. We acknowledge that without the benefit of histopathology or serial imaging, our ability to define pulmonary fibrosis is limited.
The authors posit that parenchymal bands, irregular densities, and ground glass opacities, may be considered fibrotic-like patterns. We have included irregular densities, characterized as reticulations or traction bronchiectasis, as fibrotic-like changes. We did not include parenchymal bands , as these can be associated with atelectasis, which is common in COVID and can disappear over time . Similarly, we did not include isolated ground glass opacities as fibrotic-like changes, as these have been found to decrease over time in CT lung cancer screening cohorts  and in other post COVID-19 cohorts [5, 6].
A priori, we evaluated for both previously established interstitial lung abnormality categories , as well as categories of radiographic abnormalities reported in Acute Respiratory Distress Syndrome (ARDS) survivors using an established scoring system . This inclusive approach should facilitate meta-analyses and comparisons with future studies of COVID-19 survivors, interstitial lung disease studies, and studies of non-COVID ARDS survivors. Fu...
A priori, we evaluated for both previously established interstitial lung abnormality categories , as well as categories of radiographic abnormalities reported in Acute Respiratory Distress Syndrome (ARDS) survivors using an established scoring system . This inclusive approach should facilitate meta-analyses and comparisons with future studies of COVID-19 survivors, interstitial lung disease studies, and studies of non-COVID ARDS survivors. Furthermore, it allows for future post-hoc analyses if alternate definitions of fibrotic-like patterns in COVID-19 survivors are established. Additionally, we showed that objective quantitative analyses closely agreed with visual assessments (Figure S2). These types of quantitative imaging analyses may facilitate the convergence of data from multiple centers if imaging protocols become more standardized .
Efforts are underway to characterize pulmonary impairments and radiographic abnormalities in our cohort over time in order to assess longitudinal evolution. We acknowledge that our findings do not exclude the possibility of pre-existing lung disease and we therefore look forward to reviewing independent studies, such as the Collaborative Cohort of Cohorts for COVID-19 Research (C4R)  project, which will provide better understanding of radiographic changes by comparing chest imaging studies before and after SARS-CoV-2 infection.
1. McGroder, C.F., et al., Pulmonary fibrosis 4 months after COVID-19 is associated with severity of illness and blood leucocyte telomere length. Thorax, 2021.
2. Pulmonary Parenchymal Band. Available from: https://www.ncbi.nlm.nih.gov/medgen/978776.
3. Kong, M., et al., Evolution of chest CT manifestations of COVID-19: a longitudinal study. J Thorac Dis, 2020. 12(9): p. 4892-4907.
4. Jin, G.Y., et al., Interstitial lung abnormalities in a CT lung cancer screening population: prevalence and progression rate. Radiology, 2013. 268(2): p. 563-71.
5. Nagpal, P., et al., Case Studies in Physiology: Temporal Variations of the Lung Parenchyma and Vasculature in Asymptomatic COVID-19 Pneumonia: A Multi-Spectral CT Assessment. J Appl Physiol (1985), 2021.
6. Liu, D., et al., The pulmonary sequalae in discharged patients with COVID-19: a short-term observational study. Respir Res, 2020. 21(1): p. 125.
7. Hatabu, H., et al., Interstitial lung abnormalities detected incidentally on CT: a Position Paper from the Fleischner Society. Lancet Respir Med, 2020. 8(7): p. 726-737.
8. Burnham, E.L., et al., Chest CT features are associated with poorer quality of life in acute lung injury survivors. Crit Care Med, 2013. 41(2): p. 445-56.
9. Nagpal, P., et al., Quantitative CT imaging and advanced visualization methods: potential application in novel coronavirus disease 2019 (COVID-19) pneumonia. BJR Open, 2021. 3(1): p. 20200043.
10. Collaborative Cohort of Cohorts for COVID-19 Research. Available from: https://c4r-nih.org/content/overview.
We have read with great interest the article investigating the relationship between computed tomography (CT) findings of the patients with fibrotic-like patterns and telomere length after four months of acute COVID-19 infection. According to the literature and our experience, post-COVID interstitial lung disease is a potential public health problem. Thus, we aimed to share our concerns about the fibrotic-like patterns in this group of patients.
Post-COVID fibrosis is not as the same as the other interstitial lung diseases. In the article, the authors describe CT findings of fibrotic-like patterns as limited to reticulation, honeycomb cysts, and traction bronchiectasis. However, post-COVID fibrosis CT findings were shown to be more varied and may include parenchymal bands, irregular densities, and ground-glass areas (1–3). As we move towards the future, all of us need to create a common language, a lingua franca in the definition of post-COVID fibrosis. To achieve this, we need brainstorming and close cooperation.
It will also be helpful to elaborate the characteristics of the non-fibrotic pattern in the table. The clinical importance of the ground glass areas, which persist four months after active infection but not defined as fibrotic, is unknown. We consider that these patterns cannot be separated from fibrotic-like patterns precisely. Additionally, we can also classify parenchymal bands as fibrosis-like appearance. In our experience...
It will also be helpful to elaborate the characteristics of the non-fibrotic pattern in the table. The clinical importance of the ground glass areas, which persist four months after active infection but not defined as fibrotic, is unknown. We consider that these patterns cannot be separated from fibrotic-like patterns precisely. Additionally, we can also classify parenchymal bands as fibrosis-like appearance. In our experience, subpleural parenchymal bands are not uncommon. Furthermore, respiratory symptoms may persist in patients with parenchymal bands. So, this pattern should be considered as a part of fibrotic-like pattern.
Another challenge is the lack of proof regarding fibrosis development due to COVID-19 infection. For example, honeycomb cysts are an indicator of irreversible fibrosis, and it is uncertain whether they are present in the previous CT images or not. A similar condition may apply to irregular reticulation and traction bronchiectasis. The development of fibrotic patterns may also differ from the images during the active infection (4). It may be instructive to examine the process by which signs of active involvement evolve into fibrosis, as well as the development of a fibrotic-like pattern.
We need a more precise interpretation of the development of fibrotic-like patterns. Therefore, we suggest analysing subtypes of post-COVID fibrosis, compare present findings on CT with long-term follow-up images. Also, it might be beneficial to show, if possible, that there is no fibrotic pattern in the CTs before acute Covid 19 infection.
1. Huang W, Wu Q, Chen Z, Xiong Z, Wang K, Tian J, et al. The potential indicators for pulmonary fibrosis in survivors of severe COVID-19. Vol. 82, Journal of Infection. 2021.
2. Myall KJ, Mukherjee B, Castanheira AM, Lam JL, Benedetti G, Mak SM, et al. Persistent Post-COVID-19 Interstitial Lung Disease. An Observational Study of Corticosteroid Treatment. Ann Am Thorac Soc. 2021;18(5).
3. Shah AS, Wong AW, Hague CJ, Murphy DT, Johnston JC, Ryerson CJ, et al. A prospective study of 12-week respiratory outcomes in COVID-19-related hospitalisations. Vol. 76, Thorax. 2021.
4. Guan CS, Wei LG, Xie RM, Lv Z Bin, Yan S, Zhang ZX, et al. CT findings of COVID-19 in follow-up: Comparison between progression and recovery. Diagnostic Interv Radiol. 2020;26(4):301–7.