Description

A patient with a history of non-abdominal malignancy presented after treatment for a follow-up PET/CT scan. Pertinent medical history included essential hypertension and type II diabetes mellitus. The patient's medications included metformin, furosemide and metoprolol. The PET/CT scan demonstrated diffusely increased 18-FDG uptake throughout the small and large intestine with SUVs of up to 21.3 (figure 1). The differential diagnosis for increased bowel uptake on PET/CT examination is broad and includes neoplasm, infection and inflammation with a myriad of aetiologies. However, diffuse, intense bowel uptake in a patient with diabetes is characteristic of uptake secondary to treatment with metformin.

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Figure 1

Multiplanar CT, PET and overlay images of the abdomen reveal intense uptake of 18-FDG throughout the visualised bowel, secondary to metformin therapy.

Metformin (dimethylbiguanide) is an oral biguanide used to treat diabetes mellitus. In a rodent model, metformin treatment increased intestinal glucose uptake by up to 60% in hyperglycaemic conditions, which likely accounts for the imaging findings.1 A recent study shows cessation of metformin 2 days before PET/CT examination markedly decreased the level of intestinal uptake without adversely effecting blood glucose levels.2 ,3

As the role of PET/CT in the management of malignancy continues to increase, understanding potential pitfalls and normal variation will be crucial for its successful implementation. Concurrently, a worldwide obesity epidemic has developed over the past decades resulting in a huge increase in type II diabetes mellitus, especially in the Western world. Therefore, an understanding of this interesting and potentially limiting PET/CT finding associated with the use of metformin, an extremely common agent used for the treatment of type II diabetes, will be crucial to the successful acquisition and interpretation of these studies.