Gangrene

Dry gangrene is a form of coagulative necrosis that develops in ischemic tissue, where the blood supply is inadequate to keep tissue viable. It is not a disease itself, but a symptom of other diseases.[10] The term dry is used only when referring to a limb or to the gut (in other locations, this same type of necrosis is called an infarction, such as myocardial infarction).[11] Dry gangrene is often due to peripheral artery disease, but can be due to acute limb ischemia. As a result, people with atherosclerosis, high cholesterol, diabetes and smokers commonly have dry gangrene.[12] The limited oxygen in the ischemic limb limits putrefaction and bacteria fail to survive. The affected part is dry, shrunken, and dark reddish-black. The line of separation usually brings about complete separation, with eventual falling off of the gangrenous tissue if it is not removed surgically, a process called autoamputation.[12]

Dry gangrene is the result of chronic ischemia without infection. If ischemia is detected early, when ischemic wounds rather than gangrene are present, the process can be treated by revascularization (via vascular bypass or angioplasty).[13] However, once gangrene has developed, the affected tissues are not salvageable.[14] Because dry gangrene is not accompanied by infection, it is not as emergent as gas gangrene or wet gangrene, both of which have a risk of sepsis. Over time, dry gangrene may develop into wet gangrene if an infection develops in the dead tissues.[15]

Diabetes mellitus is a risk factor for peripheral vascular disease, thus for dry gangrene, but also a risk factor for wet gangrene, particularly in patients with poorly controlled blood sugar levels, as elevated serum glucose creates a favorable environment for bacterial infection.[16]

Wet gangrene of the foot.

Wet, or infected, gangrene is characterized by thriving bacteria and has a poor prognosis (compared to dry gangrene) due to sepsis resulting from the free communication between infected fluid and circulatory fluid. In wet gangrene, the tissue is infected by saprogenic microorganisms (Clostridium perfringens or Bacillus fusiformis, for example), which cause tissue to swell and emit a foul odor. Wet gangrene usually develops rapidly due to blockage of venous (mainly) or arterial blood flow.[12] The affected part is saturated with stagnant blood, which promotes the rapid growth of bacteria. The toxic products formed by bacteria are absorbed, causing systemic manifestation of sepsis and finally death. The affected part is edematous, soft, putrid, rotten, and dark.

Because of the high mortality associated with infected gangrene (about 80% without treatment and 20% with treatment), an emergency salvage amputation, such as a guillotine amputation, is often needed to limit systemic effects of the infection.[17] Such an amputation can be converted to a formal amputation, such as a below- or above-knee amputation.[17]

Gas gangrene is a bacterial infection that produces gas within tissues. It can be caused by Clostridium, most commonly alpha toxin-producing C. perfringens, or various nonclostridial species.[8][18] Infection spreads rapidly as the gases produced by the bacteria expand and infiltrate healthy tissue in the vicinity. Because of its ability to quickly spread to surrounding tissues, gas gangrene should be treated as a medical emergency.

Gas gangrene is caused by bacterial exotoxin-producing clostridial species, which are mostly found in soil, and other anaerobes such as Bacteroides and anaerobic streptococci. These environmental bacteria may enter the muscle through a wound and subsequently proliferate in necrotic tissue and secrete powerful toxins that destroy nearby tissue, generating gas at the same time. A gas composition of 5.9% hydrogen, 3.4% carbon dioxide, 74.5% nitrogen, and 16.1% oxygen was reported in one clinical case.[19]

Gas gangrene can cause necrosis, gas production, and sepsis. Progression to toxemia and shock is often very rapid.[20]

• Necrotizing fasciitis, also known as hemolytic streptococcal gangrene, is a very rare infection that spreads deep into the body along tissue planes. It is characterized by infection with S. pyogenes, a gram-positive cocci bacteria.[21]
• Noma is a gangrene of the face most often found in Africa, Southeast Asia and South America.[22]
• Fournier gangrene is a type of necrotizing fasciitis that usually affects the genitals and groin.[23]
• Venous limb gangrene may be caused by heparin-induced thrombocytopenia and thrombosis.[24]
• Severe mesenteric ischemia may result in gangrene of the small intestine.
• Severe ischemic colitis may result in gangrene of the large intestine.

Exercises such as walking and massage therapy may be tried.[12]

Medications may include pain management, medications that promote circulation in the circulatory system and antibiotics. Since gangrene is associated with periodic pain caused by too little blood flow, pain management is important so patients can continue doing exercises that promote circulation. Pain management medications can include opioids and opioid-like analgesics. Since gangrene is a result of ischemia, circulatory system management is important. These medications can include antiplatelet drug, anticoagulant, and fibrinolytics. As infection is often associated with gangrene, antibiotics are often a critical component of its treatment. The life-threatening nature of gangrene requires treatment with intravenous antibiotics in an inpatient setting.[12] Antibiotics alone are not effective because they may not penetrate infected tissues sufficiently.[25]

Surgical removal of all dead tissue, however, is the mainstay of treatment for gangrene. Often, gangrene is associated with underlying infection, thus the gangrenous tissue must be debrided to hinder the spread of the associated infection. The extent of surgical debridement needed depends on the extent of the gangrene and may be limited to the removal of a finger, toe, or ear, but in severe cases may involve a limb amputation.[12]

Dead tissue alone does not require debridement, and in some cases, such as dry gangrene, the affected part falls off (autoamputates), making surgical removal unnecessary. Waiting for autoamputation, however, may cause health complications as well as decreased quality of life.[12]

After the gangrene is treated with debridement and antibiotics, the underlying cause can be treated. In the case of gangrene due to critical limb ischemia, revascularization can be performed to treat the underlying peripheral underlateral artery disease.

Ischemic disease of the legs is the most common reason for amputations. In about a quarter of these cases, the other side requires amputation in the next three years.[26]

Angioplasty should be considered if severe blockage in lower leg vessels (tibial and peroneal artery) leads to gangrene.[27]

Hyperbaric oxygen therapy treatment is used to treat gas gangrene. It increases pressure and oxygen content to allow blood to carry more oxygen to inhibit anaerobic organism growth and reproduction.[28]

Regenerative medical treatments and stem-cell therapies have successfully altered gangrene and ulcer prognosis.