Pathophysiology. Etiology and classification

Etiology and classification

Necrotizing Soft Tissue Infections

Summary

Most adenopathy in children is non-pathologic and spontaneously resolves. Pathologic lymphadenopathy has a large differential diagnosis, with viral lymphadenitis being the most common. Surgical consultation is often obtained when the lymph nodes do not spontaneously resolve, if there is concern for malignancy, or if there is a diagnostic dilemma. The surgeon's role is usually limited to FNA, excisional biopsy, incision and drainage.

Necrotizing soft tissue infection is a rare but very severe type of bacterial infection. It is defined as necrotising infection involving any layer of the deep soft tissue compartment (dermis, subcutaneous tissue, fascia or muscle). The word "necrotizing" refers to something that causes body tissue to die.

Necrotizing infections are characterized by destruction of the soft tissues, systemic toxicity, and a high mortality. A variety of names have been applied to these aggressive infections. Necrotizing fasciitis, hospital gangrene, Meleney cellulitis, synergistic cellulitis, synergistic necrotizing cellulitis, hemolytic streptococcal gangrene, acute dermal gangrene and the popular lay term "flesh-eating bacteria" have all been used to describe a process in which there is extensive tissue destruction, thrombosis of arterioles, and bacteria easily spreading along fascial planes.

Organisms spread from the subcutaneous tissue along the superficial and deep fascial planes. Muscle is usually spared; however, myonecrosis can occur due to compartment syndrome. Various bacteria may be involved, and necrotising fasciitis (NF) infections have been classified into:

v Type 1 - polymicrobial infection with aerobic and anaerobic bacteria; usually in patients with immunocompromise or chronic disease.

v Type 2 - monomicrobial infection - Group A streptococcus (GAS): occurs in any age group and in otherwise healthy people; occasionally accompanied by staphylococcal infection.

Type 3 - gas gangrene, or clostridial myonecrosis

The disease is more common in adults but it is certainly not unheard of in children.

"Flesh-eating bacteria" is a misnomer, as the bacteria do not actually "eat" the tissue. They cause the destruction of skin and muscle by releasing toxins (virulence factors), which include streptococcal pyogenic exotoxins. Streptococcus pyogenes produces an exotoxin known as a superantigen. This toxin is capable of activating T-cells non-specifically, which causes the overproduction of cytokines and severe systemic illness (Toxic shock syndrome).

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