What is gangrene?|
Gangrene is the term given to a condition where an area of tissue becomes necrotic (dies) and is then subsequently invaded or "digested" by bacteria. It can be classified into two types according to the cause of the underlying tissue necrosis:
Wet gangrene (also known as primary gangrene)
Tissue necrosis in wet gangrene is caused by a bacterial infection which breaks up and "liquefies" the cells of the infected tissue (hence the term wet gangrene).
What is known as "gas gangrene" is a particularly dangerous type of wet gangrene caused by a bacterial strain known as clostridium (although other bacterial strains have also been implicated). Clostridium bacteria are found in the soil and are one of a large number of bacteria found normally on our own skin and inside our intestinal tract. The presence of these bacteria on our bodies usually does us no harm at all, because they require an environment low in oxygen to grow.
Such conditions are thankfully quite rare in the human body, usually occurring only in areas of tissue that have already been severely traumatised (eg. gas gangrene has been responsible for a very large number of deaths during war). Occasionally, spontaneous infection (that is, without prior tissue injury) and tissue destruction with clostridium occurs, but usually only in individuals with an underlying condition that makes them more susceptible to infection (such as cancer, diabetes and suppression of the immune system).
Tissue destruction in gas gangrene (which particularly affects muscle cells) is caused by a toxin produced by the clostridium bacteria which breaks down the lining or membrane that surrounds all of our cells. A foul smelling gas is also produced.
Dry gangrene (also called secondary gangrene)
In dry gangrene the tissue necrosis is caused by some factor other than a bacterial infection, usually an interruption of the blood supply to the tissue. This may occur as a result of a number of conditions, including:
- arteriosclerosis (hardening and narrowing of the arteries)
- thrombosis (a clot in a blood vessel)
- frostbite (extreme cold)
- diabetes mellitus (condition associated with impaired circulation, especially in the toes)
The subsequent invasion and "digestion" of the dead tissue by bacteria is usually a less dominant process as occurs in wet gangrene, with little tissue liquefaction resulting (hence the term dry gangrene). However, an area of dry gangrenous tissue may become "wet", if subsequently infected with clostridium bacteria, for example.
The principle symptom of gangrene is excruciating pain in the area where the tissue is dying. The dead tissue turns black and looses sensation altogether (it becomes numb). In the case of dry gangrene, because the bacterial component of the conditions is usually not very prominent, it is generally only the tissue to which the blood supply has been blocked which is affected. That is, it does not spread to surrounding tissue (unless it turns into wet gangrene). Wet gangrene, on the other hand, spreads to surrounding tissue as the infection causing the condition spreads.
In the case of wet gangrene that occurs in the absence of any prior tissue injury, there are initially no obvious signs of infection on the skin surface. As the infection spreads and develops, the overlying skin becomes discoloured (a red/brown colour), swollen (as fluid and gas build up under the skin surface) and blistered.
Diagnosis of gangrene
Gangrene is diagnosed by its clinical appearance. In dry gangrene, as the cause is usually due to impaired blood supply to the affected areas. Clinical examination of the pulse reveals absent or weakened pulsation of the arteries. Wet gangrene is associated with bacterial infection. Diagnosis i