Axillary lymph nodes' response to pneumococcal polysaccharide vaccination on FDG-PET/CT examination: Two case reports

Positron emission tomography/computed tomography (PET/CT) with radioactive Fluorine-18 fluorodeoxyglucose (FDG) is a highly sensitive tool that is used for detecting malignancy. However, it can sometimes produce false positive results if done after vaccination. To prove this, we present two cases of individuals who received pneumococcal polysaccharide vaccination (PPV) and later showed FDG accumulation in the axillary lymph nodes during PET/CT scans. The first case involves a 69-year-old man who underwent a PET/CT scan for a health checkup. The scan revealed low-grade FDG uptake in the left axillary lymph nodes. A thorough examination of his medical history revealed that the patient had received PPV in his left upper arm eight days prior to the checkup. The vaccination was suspected to have caused left axillary lymphadenopathy. The second case involves a 66-year-old woman who also underwent a PET/CT scan for a health checkup. The scan showed FDG-avid lymph nodes in the left axillary region and increased FDG uptake in the spleen. After further questioning, it was discovered that the patient had received PPV in her left upper arm eight days prior to the checkup. Seven days after the PET/CT scan, when a complete blood count with differential was performed on the second case, it revealed that all data were within normal limits. Further, an abdominal ultrasound was conducted, which showed normal findings in the spleen. Based on these results, the medical team concluded that the prior vaccination was the cause of the observed benign findings and emphasized the importance of carefully reviewing patient history to differentiate between benign findings and malignant lesions.