In a patient with sepsis and a diabetic foot ulcer, what is the next best step to evaluate extent of infection?

• A. MRI of the foot
• B. Ultrasound of the foot
• C. CT scan of the foot
• D. XR of the foot to look for gas or presence of septic arthritis

Answer: (D)

In a septic patient with a diabetic foot ulcer, the priority is to rapidly assess how far the infection has spread and whether there is gas in the soft tissues or joint involvement, both of which signal a serious, potentially life‑threatening infection. A plain X‑ray of the foot is the fastest, most accessible test to detect subcutaneous gas and to look for signs of septic arthritis or osteomyelitis. Finding gas in soft tissues is a clue to a gas-forming infection, which often requires urgent surgical intervention alongside antibiotics.

MRI can be more sensitive for detecting osteomyelitis and delineating soft tissue involvement, but it takes longer and may not be immediately available in an unstable/septic patient. Other modalities like ultrasound or CT have their uses, but the initial step to quickly evaluate extent in this scenario is a radiograph to identify gas and joint/bone involvement, guiding urgent management.