Herpes Zoster Mimicking Recurrence of Lymphoma on PET/CT

Herpes zoster is a relatively common disease characterized by the eruption of vesicles in a dermatomal distribution. It is postulated to occur when the cell-mediated immunity falls below a critical level, allowing dormant virus to replicate and infect the host. Herpes zoster is known to occur more frequently in immunocompromised groups such as oncology patients receiving chemotherapy and radiation. Patients after stem cell transplant have also been reported to be predisposed to herpes virus infection. F-18-FDG PET is widely used in oncology imaging to determine the presence of metabolic activity in certain malignancies, including lymphoma. However, inflammatory cells can also have high metabolic activity and display avid uptake of FDG. This case illustrates the importance of recognizing the possibility of an inflammatory process such as herpes zoster occurring on PET/CT imaging in an oncology patient being evaluated for malignant disease.