Idiopathic necrotizing fasciitis: recognition, incidence, and outcome of therapy.

Early recognition and treatment of necrotizing fasciitis (NF) is essential for survival. The diagnosis of primary or idiopathic NF may be particularly challenging because it occurs in the absence of a known causative factor or portal of entry for bacteria. Patients with NF treated between 1989 and 1993 were reviewed to determine the incidence, clinical features, bacteriology, and results of treatment in patients with idiopathic NF. Idiopathic NF occurred in nine (18%) of 51 patients, five men and four women, ranging in age from 21 to 67 years. Associated conditions included diabetes mellitus (4), alcoholism (3), remote infection (3), and pregnancy (2). NF affected the lower extremity in eight and the perineum in one patient. Pain and tenderness occurred in all patients, soft tissue gas was recognized in two, and the presence of erythema and edema was variable. Idiopathic NF was monomicrobial in seven (78%) patients, compared to 21 per cent of patients with secondary NF (P = 0.003). S. pyogenes was the causative organism in five of seven monomicrobial infections. Time from admission to operation was significantly longer (62.3 +/- 54.8 hours) in patients with idiopathic NF compared to patients with secondary NF (17.0 +/- 16.6 hours) (P = 0.001). Treatment included operative debridement (means = 3.3) and limb amputation (n = 1) to control infection. Three patients (33%) with idiopathic NF died. Primary or idiopathic NF is principally a monomicrobial infection usually caused by S. pyogenes that most commonly occurs in the extremities. Mortality is high but is comparable to secondary NF. It is important to recognize that NF may occur spontaneously, and it should be suspected in patients with unexplained soft tissue pain and tenderness.