Will PET scan show false positive lymph node after flu shot?

Question

Hello doctor,

I am a community pharmacist. I offered a flu shot to a newly diagnosed nasopharyngeal cancer patient. The patient then went in for a PET scan three days later. I did not know that the immune response could produce false positive results. Please answer the following questions: Did the flu shot cause false positive uptake in this patient's lymph nodes? If yes, will it be only in the axillary lymph nodes or all the nodes? How significant is this in affecting the PET scan result? Can I do anything for this patient? For future reference, what is the minimum time interval between the flu shot and the PET scan?

Kindly advise.

Answer 1

Hello,

Welcome to icliniq.com.

Yes, it is quite possible that a flu shot could lead to inflammation of the nodes in the draining area of the shot. This could be detected on a PET-CT (positron emission tomography-computed tomography). In general, the SUVmax (standardised uptake value) of inflammation will be lower than that of cancer. If possible, the flu shot should be delayed. If the flu shot has been given, the PET-CT should not be delayed if it is being done for a newly diagnosed cancer (as in your case). The doctor reporting the PET scan should be aware of the flu shot. On the other hand, if a patient is undergoing a PET CT on follow-up, the scan could be delayed for six weeks, so the inflammation should have reduced.

I hope this helps.

Thank you.