Mild SARS-CoV-2 Infection with the Omicron Variant Mimicking Metastatic Cancer on Whole-Body 18-F FDG PET/CT Imaging

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a case report in which the authors present a case with pathologic FDG uptake in multiple sites mimicking metastatic disease, however most of which eventually turned out to be due to recent Covid infection with omicron variant. The case report may be of interest to the professionals in the field in a way that Covid infection may show atypical manifestations and FDG PET imaging may be misleading due to infectious/inflammatory etiology. The case was quite adequately written and supported by some additional interventions including tissue diagnosis along with PET imaging. These may be accepted as strong aspects of the case report. But there are still some missing aspects that shoud be further addressed by the authors as follows:

1) As far as it is understood, the main reason for FDG imaging in the first place is to rule out cardiac myxoma, which does not sound like a very solid indication for FDG PET/CT imaging. Did the patient undergo any other modality (cardiac MR?) for that?

2) The second FDG PET shows stable uptake on thyroid along with decreased uptake on body of T10 vertebra, as the authors state. The thyroid uptake turned out to be due to low grade thyroid papillary cancer and the vertebral biopsy did not show any malignancy on further work up. What was the CT component of the T10 vertebra like both in the first and second FDG PET imaging? Was there a lytic lesion that needed a biopsy? The authors should explain the CT features as well for the interpretation and further follow-up.

3) Following the second FDG PET scan and further work up, It seems that the initial FDG uptake in the terminal ileum and surrounding small lymph nodes were due to Covid infection. How do the authors make sure that this is true? I think there is always a possibility for another coincidental inflammatory etiology causing this ileal uptake and not just covid itself. The authors should not make solid  conclusions just depending on the changes of activity pattern on FDG PET scan, which is not specific for Covid manifestation. But of course, no one can discard the possibility of covid manifestation. This needs to be explained more precisely, not leading to solid conclusions.

 

Thank you.

Author Response

Dear Reviewer,

We appreciate your comments to the manuscript and we fully agree upon them. We have added comments to the manuscript in the description of the case and in the conclusion. Please see the specific comments below.  

Comment 1: As far as it is understood, the main reason for FDG imaging in the first place is to rule out cardiac myxoma, which does not sound like a very solid indication for FDG PET/CT imaging. Did the patient undergo any other modality (cardiac MR?) for that?

Reply: The patient was inititally evaluated for a possible myxoma. The echocardiography could not localize it precisely (within the atriae or outside). A cardiac MRI was performed that localized it behind the atriae, but in order to fully evaluate whether it was benign or not, a PET/CT was performed to examine whether the metabolic activity was increased. On the other hand, we do not know why the secondary hospital chose to do a whole-body exam, but it could be local recommandations in the evaluation of possible malignant diseases.

Comment 2: The second FDG PET shows stable uptake on thyroid along with decreased uptake on body of T10 vertebra, as the authors state. The thyroid uptake turned out to be due to low grade thyroid papillary cancer and the vertebral biopsy did not show any malignancy on further work up. What was the CT component of the T10 vertebra like both in the first and second FDG PET imaging? Was there a lytic lesion that needed a biopsy? The authors should explain the CT features as well for the interpretation and further follow-up.

Reply: The CT component of the vertebrae did not show any correllation to the increased metabolic activity. A further MRI of the vertebrae did show diffuse activity in the body of Th10 and in a more localized round area in the body of Th12. The orthopedic surgeon hence chose to take the biopsy specimen from Th12. The follow-up CT component showed the same results. This has been elaborated in the manuscript (line number 69 to 76). 

Comment 3: Following the second FDG PET scan and further work up, It seems that the initial FDG uptake in the terminal ileum and surrounding small lymph nodes were due to Covid infection. How do the authors make sure that this is true? I think there is always a possibility for another coincidental inflammatory etiology causing this ileal uptake and not just covid itself. The authors should not make solid  conclusions just depending on the changes of activity pattern on FDG PET scan, which is not specific for Covid manifestation. But of course, no one can discard the possibility of covid manifestation. This needs to be explained more precisely, not leading to solid conclusions.

Reply: We admit that our conclusion was too solid. It could be some other condition leading to the increased metabolism seen on FDG-PET. We have changed the text in the conclusion of the manuscript according to this (line 129 to 130). 

We hope that our comments are satisfactory and are happy to answer further questions or adjust the manuscript if needed. 

 

Sincerely, 

Gunnhild Helmsdal, corresponding author

 

Reviewer 2 Report

Comments and Suggestions for Authors

the case report in well conducted.

This finding may be useful in clinical practice

Author Response

Thank you for accepting to review our manuscript. We are happy that you find it well conducted and useful in clinical practice. 

Sincerely, 

Gunnhild Helmsdal, corresponding author

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

It is apparent that the authors put effort to make their best to comply with the referees' suggestions. Therefore, the revised version of the manuscript seems more comprehensive and easier to follow for the reader from a logical point of view. This case report may be of impact for the professionals especially medical imaging professionals to induce awareness about various effects of SARS-COV2 infection and much more the prolonged inflammatory changes which may exert direct effects of FDG PET/CT imaging.