The common cause of either wet or dry gangrene is loss of an effective local blood supply to any tissue. Loss of the blood supply means tissues are deprived of oxygen, thus causing the cells in the tissue to die. The most common causes of tissue blood supply loss are infections, trauma, and diseases that can affect blood vessels (usually arteries).
Dry gangrene can result from any of a number of diseases or mechanisms that can reduce or block arterial blood flow. Although the most common diseases that can cause dry gangrene are diabetes, arteriosclerosis, and tobacco addiction, there are many other lesser-known diseases that can lead to this problem. For example, some autoimmune diseases that attack blood vessels (vasculitis syndromes) may result in enough damage to cause dry gangrene. In other cases, dry gangrene can result from various external mechanisms such as burns, frostbite, and arterial trauma caused by accidents, wounds, or surgery.
Wet gangrene can result from all the causes listed above for dry gangrene but always includes infection. In some cases of wet gangrene, the initial cause is considered to be the infection. Although many types of organisms (mainly bacteria) are known to participate in wet gangrene infections, the classic bacterial organism associated with wet gangrene is Clostridium perfringens, an anaerobic bacterium that grows best when oxygen is not present. These bacteria can cause myonecrosis (muscle fiber death) with their exotoxins and produce gas bubbles in the dead and dying tissues (gas gangrene). This leads to localized swelling with compression and loss of blood flow to tissue, allowing bacteria to extend the infection to the connective tissue of muscle, skin, and other areas, causing necrotizing fasciitis (death of connective tissue). Necrotizing fasciitis, in turn, allows the infection to spread, frequently with speed, out of the locally infected site to adjacent areas or to the bloodstream (sepsis). Although this cascade of events is seen with Clostridium perfringens often as the single infecting organism type, it can be caused by many other organisms, such as Streptococcus, Staphylococcus, Bacteroides, and Escherichia. Usually two or more of these organisms occur in the infection, and many investigators suggest that the organisms help each other (synergy) to extend the infection.
There are several subtypes of wet gangrene:
- Gas gangrene means gas is present in the gangrenous tissue.
- Fournier's gangrene is gangrene with necrotizing fasciitis that occurs mainly in male genitalia.
- Internal gangrene is a general term that means gangrene is affecting an internal organ. Internal gangrene types are usually named after the organ that is affected (for example, gangrene of the appendix, gangrenous gallbladder, and gangrenous bowel).
Leprosy (Hansen's disease) is not a variant of wet or dry gangrene, although it can result in local tissue loss. It is a disease caused by Mycobacterium leprae that is transferred from person to person. It causes nodules and sores. M. leprae infection slowly destroys peripheral nerve endings in digits and mucous membranes over a period of years with loss of sensation. Digits and other local areas get repeatedly injured due to sensation loss and can become mutilated or develop atrophy and be sloughed off. However, if the chronic lesions become infected with other organisms, wet gangrene can develop in patients with leprosy.
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