# FDG altered biodistribution in white adipose tissue, a rare entity: case report and review of the literature

## TL;DR

A pediatric lymphoma patient showed unusual FDG uptake in white adipose tissue after corticosteroid treatment, highlighting the need for repeat imaging to ensure diagnostic accuracy.

## Contribution

This case report identifies corticosteroid-induced FDG uptake in white adipose tissue as a rare and under-recognized phenomenon affecting PET/CT diagnostic accuracy.

## Key findings

- A 14-year-old lymphoma patient showed diffuse FDG uptake in white adipose tissue after dexamethasone treatment.
- A one-week wait after corticosteroid discontinuation normalized FDG biodistribution and improved diagnostic accuracy.
- Corticosteroid-induced adipose FDG uptake is rare and poorly understood, with limited prior case reports.

## Abstract

Altered 18F-fluorodeoxyglucose (FDG) biodistribution due to patient factors such as exercise and inadequate fasting are well established causes of limited diagnostic efficacy. In addition, medications such as G-CSF are known to affect uptake of FDG by bone marrow and spleen. In this study, we present a case of increased white adipose uptake in a pediatric lymphoma patient who recently received high dose dexamethasone and review the relevant literature regarding this rare and poorly understood pattern of altered FDG biodistribution.

A 14-year-old male patient diagnosed with B-cell lymphoblastic lymphoma underwent FDG-PET/CT for restaging shortly after completing an induction chemotherapy regimen. Images revealed diffuse FDG uptake localizing to white adipose tissue, attributed to the 29-day course of dexamethasone which was completed two days prior. A diagnostically adequate study with relative normalization of FDG biodistribution was obtained seven days later.

In our review of the literature, diffuse FDG uptake by white fat is a rare occurrence and has only been reported by a few case reports and early observational studies. In addition to patients receiving corticosteroids, other cases of medication-induced adipose remodeling such as patients receiving highly active antiretroviral therapy have been documented with similar patterns of increased white adipose tissue activity.

Corticosteroid-induced white fat uptake of FDG is a rare phenomenon that can limit diagnostic accuracy of FDG-PET/CT and necessitate repeat imaging. Current evidence suggests that a wait period of at least one week after discontinuation of corticosteroids is sufficient to allow for decreased white fat uptake and increased diagnostic accuracy.