Condition
Comments
Necrotizing soft tissue infection
Acute infection of the deep fascia, often with crepitus, bullae, and necrosis of the subcutaneous tissue, mixed flora
Cellulitis
Infection of the deep dermis and subcutaneous fat presenting with redness and erythema without the tissue destruction characteristic of NSTI
Cutaneous anthrax
Painless or pruritic eschar surrounded by edema
Hypersensitivity reaction
No fever or leukocytosis, look for history of exposure to plants or animals
Deep venous thrombosis
Usually involves the leg, look for history of hypercoagulability, immobility, and/or inflammatory state (e.g., postsurgical, malignancy)
Sweet’s syndrome (acute febrile neutrophilic dermatosis)
Acute eruption of tender erythematous plaques with vesicles, fever, and neutrophilia; classically caused by treatment with G-CSF; may involve almost any other organ system, particularly respiratory and GI tracts; also associated with pregnancy and malignancy
Pyoderma gangrenosum
Neutrophilic infiltration of the skin; exquisitely painful lesions; may involve almost any other organ system
Erythema multiforme
Erythematous or purpuric plaques and bullae with central clearing; involves the extremities, palms, and soles; associated with herpes simplex virus, mycoplasma, and malignancy
Stasis dermatitis
Dermal fibrosis and brawny edema secondary to venous incompetence; may become acutely inflamed with crusting and exudate; look for evidence or history of venous incompetence and DVT
What Is the Most Likely Diagnosis?
In a diabetic patient presenting with a painful, erythematous, swollen leg with bullae and violaceous skin along with radiographic evidence of gas bubbles within the soft tissues of the leg, the most likely diagnosis is necrotizing soft tissue infection (NSTI).
History and Physical Examination
What Is the Implication of Crepitus?
Crepitus implies the presence of gas within the tissues, most likely due to the presence of gas-forming organisms.
What Are the Risk Factors for NSTI?
Factors that depress immunity and/or decrease tissue perfusion increase the risk for NSTI including diabetes mellitus, malnutrition, intravenous (IV) drug abuse, obesity, chronic alcohol abuse, chronic lymphocytic leukemia, chronic steroid use, renal failure, peripheral arterial disease, and cirrhosis.
Watch Out
NSTI is also seen following traumatic extremity injuries particularly in association with gross wound contamination and in postsurgical wounds.
What Is the Implication of Bullae? Violaceous Skin?
The presence of bullae implies partial tissue death within the layers of the skin that allows for the collection of fluid between tissue layers. Violaceous skin implies a violet or purple discoloration secondary to ischemia.
What Are the “Hard Signs” of Necrotizing Soft Tissue Infection (NSTI)? What Percent of Patients with NSTI Have Such Hard Signs?
Hypotension, crepitus, skin necrosis and bullae, and gas on X-ray are “hard signs” of NSTI. However, it has been shown that less than half of patients with NSTI will have hard.
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