Systemic Immune Response to Vaccination on FDG-PET/CT

Area of Science:

• Nuclear Medicine
• Oncology
• Immunology

Background:

• Fluorodeoxyglucose (FDG) uptake on PET/CT scans can be affected by inflammatory processes.
• Systemic immune responses, such as those following vaccination, may manifest as increased FDG avidity.
• Differentiating benign inflammatory uptake from malignant progression is crucial for patient management.

Purpose of the Study:

• To report a case of increased splenic and axillary lymph node FDG uptake following influenza vaccination in a lung cancer patient.
• To emphasize the importance of clinical history in interpreting FDG-PET/CT findings.
• To illustrate how recognizing vaccination-related uptake can prevent misdiagnosis and inappropriate treatment changes.

Main Methods:

• A patient diagnosed with lung cancer underwent FDG-PET/CT.
• Clinical history was obtained, revealing recent influenza vaccination.
• Serial FDG-PET/CT scans were reviewed to assess the temporal course of FDG uptake.

Main Results:

• Transient FDG-avid left axillary lymph nodes and intense splenic FDG uptake were observed.
• The uptake correlated temporally with a recent influenza vaccination.
• This pattern represented a systemic immune response to the vaccine.

Conclusions:

• Influenza vaccination can cause significant splenic and lymph node FDG uptake on PET/CT.
• Considering vaccination history is essential to avoid misinterpreting this uptake as cancer progression.
• Accurate interpretation prevented false-positive findings and unnecessary alterations to the lung cancer treatment plan.