Impact of Thymic Response in COVID-19 Pneumonia on Disease Severity and Mortality-As Assessed on CT-Chest

Abstract

Objective: To determine the effect of thymic response to COVID-19 pneumonia on imaging and its impact on disease severity and outcome.

Study Design: Cross-sectional study.

Place and Duration of Study: Armed Forces Institute of Radiology and Imaging (AFIRI), Rawalpindi Pakistan, from Mar to Jul 2020.

Methodology: A total of 1620 COVID-19 patients above the age of 18, of either gender, were included in the study. Their findings on High-Resolution CT (HRCT) chest were recorded and graded according to the CT severity score (CTSS) out of a total of 40; less than or equal to 19 was taken as mild while >20 scores were considered as severe disease. The thymic response was assessed by imaging appearance on CT and was graded from 0-3 as follows: fatty, predominantly fatty, mixed density (fat and soft density), and soft density. Fatty replacement implied thymic involution, while soft density depicted a reactivation of thymic tissue after a disease process depictive adequate thymic response.

Results: A significant difference in thymic response was observed in patients of different age groups (p<0.001), with the younger age group demonstrating thymic reactivation/ response in the majority (170/244, 69.7%). CT severity score and mortality were significantly higher in older patients demonstrating poor thymic response to COVID pneumonia.

Conclusion: Response of the thymus to acute viral infection by Sars COVID-19 is impaired as age progresses; this accounts for greater disease severity, morbidity and mortality in older patients.