Quantitative CT Analysis Reveals Subtle Lung Volume Reduction in Long COVID Patients

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Long COVID syndrome, characterized by persistent symptoms following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, has gained recognition in social support groups and scientific communities.

This condition affects patients across all levels of disease severity, including younger adults, children, and those who were never hospitalized.

While the precise definition of Long COVID is still lacking, fatigue and dyspnea are the most commonly reported symptoms that persist for months after acute infection. Additional persistent symptoms include cognitive and mental impairments, chest and joint pains, palpitations, myalgia, smell and taste dysfunctions, cough, headache, gastrointestinal, and cardiac issues [1].

Understanding Long COVID in Children and Young People

Contrary to the assumption that children and young people with low risk of life-threatening acute infection may not suffer long-term consequences of SARS-CoV-2, it is plausible that they are at a higher risk of developing Long COVID. The immunological susceptibility and underlying biology of Long COVID in young individuals are still poorly understood [2].

Role of Imaging in Long COVID Evaluation

Numerous studies have demonstrated that patients in the early convalescence phase after acute infection often show impaired diffusing capacity and lower respiratory muscle strength. While clinical tests such as Diffusion Lung CO, Spirometry, and 6 Minute Walking test are useful in demonstrating lung impairment in Long COVID patients, imaging plays a pivotal role [3].

Chest CT as a Diagnostic Tool

Chest CT has emerged as the best radiological test for diagnosing and monitoring patients with COVID. It has revealed various findings ranging from mild to severe in the acute course of infection. Furthermore, fibrotic-like changes, ground-glass opacities (GGOs), consolidations, pulmonary interstitial thickening, and a crazy paving pattern may persist in the early convalescence phase, even when chest CT appears normal [3]. Other imaging techniques, such as chest digital tomosynthesis (DTS) and repeated lung ultrasound, have also demonstrated similar findings [12, 13].

Persistent Lung Parenchymal Findings

Recent studies have shown that approximately 94% of hospitalized patients have persistent lung parenchymal findings on their discharge CT scans [14, 15]. However, it is important to note that lung alterations often resolve within three months, with 53% of patients experiencing resolution within three weeks, especially in cases of mild COVID. Therefore, many patients with Long COVID symptoms do not exhibit macroscopic findings on chest CT, particularly among young individuals with mild respiratory symptoms [3].

Long-Term Consequences and Fibrotic Changes

While data from previous coronavirus infections suggest the presence of substantial fibrotic long-term consequences [16, 17, 18], little is known about the long-term lung changes after COVID infection. Evaluating lung volumes can serve as a surrogate to identify this condition [3].

Quantitative Chest CT Analysis in Long COVID Patients

The aim of our study was to evaluate potential lung volume reduction in Long COVID patients who showed no lung inflammatory or fibrotic abnormalities on chest CT imaging, compared to age- and sex-matched controls. We used quantitative CT analysis to detect subtle fibrotic changes that may not be visible through standard imaging techniques.

Study Findings and Implications

Our study revealed a significant reduction in lung volume in the post-COVID group compared to the control group, despite negative chest CT scans for inflammatory findings. This suggests the presence of microscopic lung changes that may not be detectable through conventional imaging. The proportional lung volume reduction observed in both lungs indicates a widespread diffusion of the virus and global interstitial involvement, even in cases where the chest CT pattern appears localized.

Significance of Quantitative Chest CT Analysis

Quantitative chest CT analysis provides an important tool for managing Long COVID patients, as it introduces new parameters to enrich the clinical assessment of these individuals. The findings of our study suggest the presence of persistent fibrotic changes, contributing to the reduction in lung volume measurements, even when traditional imaging methods do not detect any macroscopic abnormalities.

Implications for Long COVID Care and Economic Impact

Many patients do not fully recover even months after the acute phase of COVID infection. This significant morbidity, unrelated to the severity of the acute phase, affects individuals’ perception of health, ability to return to work, and results in enduring fatigue. Providing adequate healthcare to all patients with diagnosed COVID, regardless of the need for hospitalization, becomes crucial. Additionally, the economic impact on the workforce should be considered [24].

Pulmonary Function Impairment and Long COVID

Research on the early convalescence phase of COVID suggests that pulmonary function impairment is the most common sequelae, including reductions in diffusing capacity, FEV1/FVC ratio, DLCO abnormalities, and obstructive or restrictive pulmonary dysfunction. Most of these patients do not exhibit pathological changes on chest CT scans with macroscopic findings [3].

Limitations and Future Directions

Several limitations should be acknowledged in our study, such as the use of different CT scanners, the lack of spirometry data, and the absence of information regarding the chest CT or vaccination status during the acute phase. Further research is required to address these limitations and gain a deeper understanding of Long COVID.

Conclusion

The continuous circulation of the SARS-CoV-2 virus necessitates long-term monitoring of COVID patients. Our study highlights the importance of quantitative chest CT analysis in Long COVID patients, revealing a reduction in lung volume despite negative inflammatory findings on chest CT.

These findings suggest the presence of subtle diffuse fibrotic changes that are not visible through standard imaging methods. By uncovering these microscopic alterations, quantitative CT analysis enhances the clinical assessment and understanding of Long COVID, contributing to the broader knowledge of the potential long-term effects caused by the virus.


reference link : https://www.mdpi.com/2379-139X/9/4/101

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