Flip-flop phenomenon in systemic sclerosis on fluorodeoxyglucose positron emission tomography/computed tomography.

Systemic sclerosis (SSc) is a rare autoimmune disease, which may affect multiple organ systems. Fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) can demonstrate the degree and anatomical extent of involvement in the entire body and coexisting malignancies in connective tissue diseases. We present a case of SSc with an increased 18F-FDG uptake in the cutaneous and subcutaneous tissues even higher than the neighboring skeletal muscles ("flip-flop phenomenon," that is, an increased 18F-FDG uptake in the skin but a decreased 18F-FDG uptake in the skeletal muscles).