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IMAGE INTERPRETATION · INFECTION AND INFLAMMATION

FDG PET/CT for Fever of Unknown Origin

FDG PET/CT — whole body for unknown source of infection
FDG PET/CT — whole body for unknown source of infection

CC BY-SA 4.0 · Pennradiology / Wikimedia Commons · source file

Question

A patient has a 3-week history of fever >38.3°C, weight loss, and night sweats without an identified source despite extensive workup (blood cultures, CT, echocardiography). FDG PET/CT is ordered for evaluation of fever of unknown origin (FUO). What is the PRIMARY value of FDG PET/CT in this clinical setting?

  1. AFDG PET is always negative in infection, confirming non-infectious causes
  2. BFDG PET provides a radiation-free alternative to CT
  3. CFDG PET/CT localizes occult infection, inflammation, or malignancy in approximately 50–60% of FUO cases, directing further targeted evaluation or biopsy
  4. DFDG PET replaces blood cultures as the gold standard for FUO
Show the answer and explanation

C. FDG PET/CT localizes occult infection, inflammation, or malignancy in approximately 50–60% of FUO cases, directing further targeted evaluation or biopsy

FDG PET/CT has emerged as an important diagnostic tool for fever of unknown origin (FUO) because many causes — infection (endocarditis, osteomyelitis, abscesses), vasculitis (large-vessel vasculitis such as giant cell arteritis), inflammatory conditions, and occult malignancy — show increased FDG uptake. Meta-analyses show FDG PET/CT identifies a potential diagnostic focus in ~50–60% of FUO cases, guiding further targeted evaluation or biopsy. This makes it one of the highest-yield single studies in the FUO workup algorithm. It is particularly valuable for detecting large-vessel vasculitis and lymphoma that may be missed by CT alone.

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