Gangrene may be caused by a variety of
chronic diseases and post-traumatic, post-surgical, and spontaneous
causes. There are three major types of gangrene: dry, moist, and gas
(a type of moist gangrene).
Dry gangrene is a condition that results when one or more arteries
become obstructed. In this type of gangrene, the tissue slowly dies,
due to receiving little or no blood supply, but does not become
infected. The affected area becomes cold and black, begins to dry
out and wither, and eventually drops off over a period of weeks or
months. Dry gangrene is most common in persons with advanced
blockages of the arteries (arteriosclerosis) resulting from
diabetes.
Moist gangrene may occur in the toes, feet, or legs after a crushing
injury or as a result of some other factor that causes blood flow to
the area to suddenly stop. When blood flow ceases, bacteria begin to
invade the muscle and thrive, multiplying quickly without
interference from the body's immune system.
Gas gangrene, also called myonecrosis, is a type of moist gangrene
that is commonly caused by bacterial infection with Clostridium
welchii, Cl. perfringes, Cl. septicum, Cl. novyi, Cl. histolyticum,
Cl. sporogenes, or other species that are capable of thriving under
conditions where there is little oxygen (anaerobic). Once present in
tissue, these bacteria produce gasses and poisonous toxins as they
grow. Normally inhabiting the gastrointestinal, respiratory, and
female genital tract, they often infect thigh amputation wounds,
especially in those individuals who have lost control of their bowel
functions (incontinence). Gangrene, incontinence, and debility often
are combined in patients with diabetes, and it is in the amputation
stump of diabetic patients that gas gangrene is often found to
occur.
Other causative organisms for moist gangrene include various
bacterial strains, including Streptococcus and Staphylococcus. A
serious, but rare form of infection with Group A Streptococcus can
impede blood flow and, if untreated, can progress to synergistic
gangrene, more commonly called necrotizing fasciitis, or infection
of the skin and tissues directly beneath the skin.
Chronic diseases, such as diabetes mellitus, arteriosclerosis, or
diseases affecting the blood vessels, such as Buerger's disease or
Raynaud's disease, can cause gangrene. Post-traumatic causes of
gangrene include compound fractures, burns, and injections given
under the skin or in a muscle. Gangrene may occur following surgery,
particularly in individuals with diabetes mellitus or other
long-term (chronic) disease. In addition, gas gangrene can be also
be a complication of dry gangrene or occur spontaneously in
association with an underlying cancer.
In the United States, approximately 50% of moist gangrene cases are
the result of a severe traumatic injury, and 40% occur following
surgery. Car and industrial accidents, crush injuries, and gunshot
wounds are the most common traumatic causes. Because of prompt
surgical management of wounds with the removal of dead tissue, the
incidence of gangrene from trauma has significantly diminished.
Surgeries involving the bile ducts or intestine are the most
frequent procedures causing gangrene. Approximately two-thirds of
cases affect the extremities, and the remaining one-third involve
the abdominal wall. |