Iatrogenic Cushing's syndrome on 18F-FDG-PET/CT: A pitfall in metabolic assessment of oncologic response.

Iatrogenic Cushing's syndrome has very well-known stigmata on physical examination but can pose a diagnostic challenge when it rarely presents radiologically. We present a classic albeit rarely encountered imaging appearance of Iatrogenic Cushing's on 18F-FDG-PET/CT, with diffuse subcutaneous white adipose proliferation and metabolic activation in a 7-year old patient one-month after starting a high dose steroid regimen for lymphoma. There was an extreme shift in the expected FDG biodistribution with dominant localization to the subcutaneous adipose tissue. This metabolic shift led to sub-threshold visceral biodistribution, rendering the scan non-diagnostic with regards to assessment of oncologic response. Aside from detailing the characteristic imaging findings of Iatrogenic Cushing's and its clinical importance, we discuss the physiologic basis of this imaging pattern and the rarer differential diagnosis to consider when this pattern of uptake is encountered on 18F-FDG-PET/CT.