The most likely diagnosis is: e) forefoot gangrene.

The radiographs (Figures 1a and 1b) reveal patchy lucencies between the first and second metatarsals, indicative of gas within the soft tissues (soft tissue emphysema), which is the main finding in the case leading to the correct diagnosis of foot gangrene. No acute bony abnormality is present — no fracture, erosion or signs of osteomyelitis. With the history of a foot ulcer in a diabetic patient, and no history of penetrating trauma, the presence of soft tissue emphysema is diagnostic of development of gangrene. This patient underwent below-knee amputation after the diagnosis was made (Figure 2).

The word gangrene comes from the Latin word gangraena, which means an “eating sore.” Gangrene is the term used to describe death and decay of a body part due to deficiency of blood supply with subsequent soft tissue infection, and is a frequent complication in the diabetic foot. Amputation is often required to save the proximal portion of the involved limb and/or the patient’s life.

There are over 15 million people living with diabetes in North America. Diabetic patients are four times more likely than the general population to develop peripheral artery disease. They’re five times more likely than nondiabetic individuals to develop critical limb ischemia. Approximately 25% of these patients will develop foot problems and up to 10% will undergo amputation as a result of gangrene formation. Surprisingly, foot complications account for more days in hospital than all other aspects of diabetes combined.

When there’s concern regarding possible gangrene formation in a diabetic foot, plain radiographs are usually ordered first to rule out obvious soft tissue emphysema. Nuclear medicine bone scans, combined with gallium scans, are used to rule out osteomyelitis. CT scans may help to assess for subtle soft tissue gas and/or bone destruction. More recently, MRI has been increasingly used in the evaluation of diabetic foot disease due to its superior anatomic resolution of bone and soft tissue pathology. In addition, hybrid MR angiography has been shown to be a reliable method for investigating peripheral artery disease in selected diabetic patients with critical limb ischemia. MR angiography visualizes lower extremity vessels that are not seen on conventional angiography. It avoids iodinated contrast material-induced renal failure in diabetics at risk for renal complications, and may be useful for treatment planning in this setting.

Charcot foot involves destruction and disruption of the tarsal-metatarsal articulations (LisFranc’s joint) secondary to neuropathic disease. This diagnosis is not uncommon is diabetics, due to peripheral artery disease. However, the images shown of this patient don’t reveal any abnormality of LisFranc’s joint, so this is not a good choice.

Freiberg’s infraction refers to localized osteochondritis of the 2nd metatarsal head resulting in flattening of the head, subchondral sclerosis, localized pain, and often, premature arthritis. It’s considered to represent local avascular necrosis, likely from repetitive trauma of the 2nd MT head. In the case presented, the 2nd MT head is normal in appearance so this diagnosis is not an option.

Gout in the foot typically involved the 1st MTP joint, producing paramarginal erosions and can be associated with uric acid crystal deposition in the local soft tissues resulting in punctate or flocculent soft tissue calcifications. Soft tissue emphysema is not a feature of gouty arthritis.

Madura foot, or foot mycetoma, is an uncommon debilitating chronic granulomatous disease that is prevalent in tropical and subtropical regions. The disease may be caused by a fungus (such as eumycetoma, madurella grisea or madurella mycetomatis) or by bacteria (typically actinomycetoma). Radiographs reveal extensive bony destruction from florid diffuse osteomyelitis, with associated marked soft tissue destruction. But soft tissue emphysema is not a typical feature of Madura foot.

 

References

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