Accordingly, early lung function analysis of patients with COVID-19 at the time of discharge from hospital revealed a high rate of abnormalities indicative of potential interstitial lung disease [15].
The load of fibrotic lung disease following SARS-CoV-2 infection is tending to be high, the global load of fibrotic lung disease will apparently increase remarkably [16].
The early identification of patients at higher risk of lung injury and fibrotic damage is critical and therefore the necessity of diagnostic guidance for patients with persistent pulmonary abnormalities after COVID-19 infection appears to be eminent. The final origin of fibrotic findings in the lungs remains unknown: the viral infection, the secondary cytokine cascade, related to treatment or ventilation, or a mixture of all these factors come into consideration [16].
The diagnosis of pulmonary fibrosis based on CT findings remains challenging: parenchymal bands, irregular interfaces, reticular opacities, and traction bronchiectasis with or without honeycombing not always clearly present on the follow-up CT scans [17]. Unfortunately the histological confirmation appears also oft not executable or infeasible. Non-invasive clinical diagnostic performance is extremely advisable.
We intended to explore the potential diagnostic benefit of nuclear imaging in terms of PET/CT scanning in further characterization of impaired pulmonary convalescence.
Since the 18 F-FDG-PET/CT was negative and because no improvement on high-dose corticosteroids could be observed, we then assumed the presence of underlying fibrotic repair processes. This hypothesis is backed by former studies, which investigated the diagnostic yield of 68Ga-FAPI PET/CT in lung cancer and IPF. The respective PET/CT analysis showed a low physiological background signal of FAP in tumour surrounding tissue, while increased tracer uptake in IPF-related fibrotic lesions was observed [7, 8 and 18]. Furthermore, the calculated SUVmax of 68Ga-FAPI within the fibrotic lesions was similar to the calculated SUVmax of the here presented post-Covid-19 lesions [19].
Within IgG4-related disease, 68Ga-FAPI PET/CT was able to discriminate between inflammatory and fibrotic activity [18].
Moreover, several trials (NCT04541680, NCT04619680, and NCT04607928) currently investigate the use of antifibrotic medication in COVID-19.