Gas gangrene is a bacterial infection that produces gas in tissues in
gangrene. This deadly form of gangrene usually is caused by Clostridium
perfringens bacteria. It is a medical emergency.
Myonecrosis is a condition of necrotic damage, specific to muscle tissue. It is
often seen in infections with C. perfringens or any of myriad soil-borne
anaerobic bacteria. Bacteria cause myonecrosis by specific exotoxins. These
microorganisms are opportunistic and, in general, enter the body through
significant skin breakage. Gangrenous infection by soil-borne bacteria was
common in the combat injuries of soldiers well into the 20th century,
because of nonsterile field surgery and the basic nature of care for severe
projectile wounds. Other causes of myonecrosis include
envenomation by snakes of the Bothrops genus, ischemic necrosis, caused by
vascular blockage, tumours that block or hoard blood supply, and disseminated
intravascular coagulation or other thromboses.
Features Gas gangrene can cause myonecrosis, gas
production, and sepsis. Progression to toxemia and shock is often very rapid.
It can easily be noticed by the large, blackened sores that form, as well as a
degree of loud and distinctive crepitus caused by gas escaping the necrotic
tissue. Pathophysiology
Gas gangrene is caused by exotoxin-producing Clostridium species,
which are mostly found in soil, but also found as normal gut flora, and other
anaerobes. The exotoxin is commonly found in C. perfringens type A strain
and is known as alpha toxin. This alpha toxin is a lethal toxin and also known
as phospolipase C. It increases vascular permeability and produces necrotizing
activity. These environmental bacteria may enter the muscle through a wound and
go on to proliferate in necrotic tissue and secrete powerful toxins. These
toxins destroy nearby tissue, generating gas at the same time.
Other organisms may occasionally cause gas gangrene.
A gas composition of 5.9% hydrogen, 3.4% carbon dioxide, 74.5% nitrogen, and
16.1% oxygen was reported in one clinical case.
Myonecrosis differs slightly from other types of necrosis. While the underlying
causes are almost identical, the type of affected tissue is significantly more
important for the patient's general health. Superficial necrosis is
unsightly and can lead to unattractive scarring, but otherwise does not affect
the patient's likelihood of survival or physical capability to the same extent.
However, massive myonecrosis will likely result in the loss of movement of the
entire region. If the necrotic damage is allowed to continue throughout an
affected limb, then often that entire limb is lost permanently.
It is often difficult to identify the extent of muscle damage, as C.
perfringens may be at work in deeper fascial layers below the skin. Unlike
other anaerobic infections, discharge in these infections is often not purulent.
Instead, the discharge is often described as "sweetly putrid" or
"dishwater pus" because it is much thinner than normal pus. This is due to
the lysis of neutrophils, a type of white blood cell, caused by the
lecithinases and other toxins released by Clostridium species.
Soil-borne anaerobes are particularly well-adapted to surviving harsh
conditions. Often, a scarcity of nutrition and competition for resources
from numerous other species occurs. Changes in pH and temperature are often
significant, also. Bacteria often possess the ability to create exotoxins
to assist them in competing with other microbes in their natural environments.
When such bacteria are able to enter a living host, they encounter a vast
supply of nutrients, warm conditions, and an abundance of water. This enables
the microbes to rapidly proliferate, far in excess of the immune system's
capability to defend, as prokaryotic bacteria possess a far greater capacity
for multiplication than the host's immune system. The combination of
bacterial load and ability to multiply is the basis for the microbes' ability
to cause massive infection. Alongside such rapid proliferation is a
corresponding mass-production of exotoxin that causes severe damage to
local tissue in the host. One such exotoxin is produced by C. perfringens
and is responsible for the disease manifestations. This exotoxin is known
as alpha toxin. Massive infection, gross injury, and
depletion of the host's immune capability result in system-wide sepsis.
This is partly due to the burden on the immune system, its corresponding release
of inflammatory cytokines, and the distribution of bacterial toxins.
Massive infection is likely to result in death from a combination of system-wide
septic shock and the unintentionally damaging effects of the immune response.
In animals, disability and distress caused by all of these factors markedly
increase the chance of predation. Treatment
Treatment is usually debridement and excision, with amputation necessary in
many cases. Antibiotics alone are not effective because they do not penetrate
ischaemic muscles sufficiently to be effective. However, penicillin is given
as an adjuvant treatment to surgery. In addition to surgery and antibiotics,
hyperbaric oxygen therapy is used and acts to inhibit the growth of and kill
the anaerobic C. perfringens. The growth of C. perfrigens is inhibited under
pressures above 9.5 kPa, so if started early, this condition can mostly be
cured. Additional images
See also Blackleg
List of cutaneous conditions References