Necrotizing skin infections, including necrotizing cellulitis and necrotizing fasciitis, are serious forms of cellulitis. These infections cause infected skin and tissue to die (necrosis).
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The infected skin is red, warm to the touch and swollen, and gas bubbles may form under the skin.
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The person usually has intense pain, feels very ill and has a high fever.
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The diagnosis is based on a doctor’s assessment, X-rays and laboratory tests.
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Treatment involves removing dead skin and tissue, sometimes requiring extensive surgery, and giving intravenous antibiotics.
(See also Overview of bacterial skin infections.)
Most skin infections do not result in the death of the skin and nearby tissues. Sometimes, however, a bacterial infection can cause small blood vessels in the infected area to clot. This clotting causes the tissue fed by these vessels to die from lack of blood. Dead tissue is called necrotic. Because the body’s immune system, which travels through the bloodstream (e.g white blood cells and antibodies) can no longer reach this area, the infection spreads quickly and can be difficult to control. The infection can be fatal, even with appropriate treatment.
Some necrotizing skin infections spread deep into the skin along the surface of the connective tissue that covers muscles (fascia) and are called necrotizing fasciitis. Other necrotizing skin infections spread in the outer skin layers and are called necrotizing cellulitis. Several different bacteria, such as Streptococci and Clostridiacan cause necrotizing skin infections, but in many people the infections are caused by a combination of bacteria. The necrotizing skin infection caused by streptococci in particular has been dubbed “flesh-eating disease” by the press, but it differs little from the others. Gas gangrene (also called clostridial myonecrosis) is a type of necrotizing skin infection that affects muscle and surrounding tissue and is typically caused by Clostridia.
Some necrotizing skin infections begin with puncture wounds or other skin injuries, especially wounds that are contaminated with dirt and grime. Other infections begin in surgical incisions or even in healthy skin. Sometimes people with diverticulitis, bowel perforation or tumors in the bowel can develop necrotizing infections in the abdominal wall, genitals or thighs. These infections occur when certain bacteria spread from the gut into the skin. The bacteria can initially create one abscess (a pocket of pus) in the abdominal cavity and spread directly outward to the skin, or they can spread through the bloodstream to the skin and other organs. People with diabetes, cancer, an alcohol disorder, injection drug use or chronic kidney disease, or who have a weakened immune system are at increased risk of necrotizing skin infections.
Symptoms of necrotizing skin infections
Symptoms of necrotizing skin infections often begin as the common skin infection, cellulitis. The skin may appear pale at first but may quickly become red or bronze and warm to the touch and swollen. Pain is intense.
Later, the skin becomes violet, often with the development of large fluid-filled blisters (bullae). The fluid from these blisters is brown, watery, and sometimes foul-smelling. Areas of dead skin turn black (gangrene).
Some types of necrotizing skin infection, including those caused by Clostridia and mixed bacteria, produce gas. The gas creates bubbles under the skin and sometimes in the blisters themselves, causing the skin to feel cracked when pressed. At first, the infected area is extremely painful, but as the skin dies, the nerves stop working and the area loses sensation, so the pain disappears or decreases. The muscles may be affected as the infection worsens.
The person usually feels very ill and has a high fever, rapid pulse and mental deterioration ranging from confusion to unconsciousness. Blood pressure can drop due to toxins released by the bacteria and the body’s response to the infection (septic shock). Humans can evolve toxic shock syndrome.
Diagnosis of necrotizing skin infections
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A doctor’s assessment
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Laboratory studies
A doctor makes a diagnosis of necrotizing skin infection based on its appearance, especially the presence of gas bubbles that can be seen under the skin. X-rays can also show gas under the skin.
A blood test usually shows that the number of white blood cells is increased (leukocytosis). The specific bacteria causing the infection are identified by laboratory analysis of blood or tissue samples (culture). But doctors begin treatment before they have the lab test results.
Treatment of necrotizing skin infections
The treatment of necrotizing fasciitis and gas gangrene is surgical removal of the dead tissue plus antibiotics given through a vein (intravenously). Large amounts of skin, tissue and muscle often need to be removed, and in some cases affected body parts may need to be removed (amputated).
People may need large amounts of intravenous fluids before and after surgery.
Prognosis for necrotizing skin infections
Necrotizing skin infections are fatal in about 20 to 30% of people who receive appropriate treatment. Without treatment, these infections are almost always fatal.
Older adults, those who have other chronic medical conditions, and those in whom the infection has reached an advanced stage have a worse outcome. A delay in diagnosis and treatment and inadequate surgical removal of dead tissue worsen the prognosis.
