Gangrene essentially means death of tissues due to lack of blood supply and invasion of deeper tissues with infection.

Gangrene may be broadly classified into two types – dry and wet gangrene.

There are several other types of gangrene that are rarer. However, all types of gangrene manifest either as dry or wet form.

Dry gangrene

In this type of gangrene there is obstruction or slowing of blood flow into the organ or part of the body that is affected. Peripheral parts like toes, fingers, tip of the nose, earlobes etc. are commonly involved.

Dry gangrene is usually seen in patients of type 1 and type 2 diabetes. In both types of diabetes long term high blood sugar damages the small arteries and blood vessels that supply the end parts of the body like fingers and toes. This leads to obstruction and slowing of blood flow and ultimately gangrene.

In patients with high cholesterol, or dyslipidemia, there is a risk of deposition of cholesterol and lipids called plaques within the blood vessels. In the peripheries like toes and fingers this leads to decrease in the blood vessel diameters by narrowing of the lumen. This may lead to formation of gangrene.

Patients with peripheral arterial disease develop fatty acid deposits or develop narrowing of peripheral blood vessels. Some conditions include Raynaud’s disease and Scleroderma. This restricts blood supply to hand or leg muscles and may cause gangrene.

Dry gangrene is usually characterized by cold, painless and dry and shrivelled up affected part. There is surrounding healthy skin. The area affected is said to appear mummified.

Wet gangrene

Wet gangrene occurs when infection and bacteria invade deeper tissues after injuries, frost bites, foot ulcers or burns. There is excessive swelling of the affected part due to release of the toxins from the invading bacteria.

This leads to blockage of the blood supply and worsening of the infection as the fighter cells of the body (white blood cells) cannot reach the area affected via blood vessels.

Wet gangrene can spread much quicker than dry gangrene and may lead to life-threatening complications like septic shock if not treated immediately.

Wet gangrene appears discoloured or black usually with acute and excruciating pain. There are black blisters and foul-smelling pus beneath the thinned skin at the area.

As infection is associated with release of discharge and pus, it is known as “wet”.

Other types of gangrene

Other types of gangrene include:

Gas gangrene

This is caused by bacteria called Clostridium. This is found in spores present in the soil. Gas gangrene was a common cause of death in the wars.

The gangrene is caused by the toxins released by the bacteria. This may be of three further types:

• • traumatic gas gangrene occurring after injury
  • non-traumatic gas gangrene
  • recurrent gas gangrene caused by C. perfringens species of bacteria.

Necrotising fasciitis

Necrotising fasciitis (NF) is a deep tissue infection caused by bacteria like Staphylococcus or Streptococcus. The bacteria spreads into the skin and into the tissues. This bacteria attacks the soft tissue and the fascia, which is a sheath of tissue covering the muscle. NF can occur in an extremity following a minor trauma, or after some other type of opportunity for the bacteria to enter the body such as surgery. The Group A Strep infection (flesh eating bacteria) is most common with minor trauma. A mixed bacterial infection is often the cause after surgery.

Internal gangrene

This is cause when blood supply to an internal organ is hampered usually by pressure from another organ or growth. For example, in hernia there is an abnormal opening where the intestine may get blocked and the blocked area turns gangrenous.

Noma or cancrum oris

This is a type of gangrene affecting the face.

Fournier’s gangrene

Fournier's gangrene (FG) is a rare but life threatening disease that affects the penis and the genitalia. FG has been shown to have a predilection for patients with diabetes as well as long term alcohol misuse; however, it can also affect patients with non‐obvious immune compromise.  The development and progression of the gangrene is often fulminating and can rapidly cause multiple organ failure and death. Because of potential complications, it is important to diagnose the disease process as early as possible Although antibiotics and aggressive debridement have been broadly accepted as the standard treatment, the death rate remains high.(5)

Meleney's synergistic gangrene

This is a rare type seen in patients after surgery. Meleney's synergistic gangrene is caused by S aureus and streptococcus organisms. One of the identifying symptoms is the presence of extremely painful lesions, which usually form in the second week after surgery or minor trauma. (6)