This suggests relatively low numbers of bacteria may cause cellulitis and the expanding area of erythema within the skin may be the direct result of extracellular toxins or soluble inflammation mediators elicited by the host. Early diagnosis may be difficult since pain or unexplained fever may be the only presenting symptom and sign, respectively. Next, swelling followed by brawny edema and tenderness develop. With progression, dark red induration of the epidermis appears along with bullae filled with blue or purple fluid. Later, skin becomes friable and takes on a bluish, maroon, or black color due to extensive thrombosis in blood vessels supplying the dermal papilla.
Infection spreads rapidly along fascial planes and through venous and lymphatic channels.
Patients in the later stages are toxic and frequently manifest shock and multiorgan failure. Prompt surgical exploration down to the deep fascia and muscle is essential. The cause can be carcinoma, diverticulosis, thrombosed hemorrhoid, anal fissure, or a urethral tear. Frequently, necrotizing fasciitis develops in patients with peripheral vascular disease, diabetes mellitus, or following either surgery or penetrating injury to the abdomen. Leakage into the perineal area results in a syndrome called Fournier's gangrene which is characterized by massive swelling of the scrotum and genitals with extension into the perineum, anterior abdominal wall, and lower extremities.