Chapter 8 – INFECTIONS OF THE DIABETIC FOOT

A small cut on a diabetic foot can lead to a serious infection. Although the end result of a foot infection might be loss of a leg, life, or both, the initial event can be so trivial that even a non-diabetic person might dismiss it. It may start with a minor incident such as stepping on a piece of glass, a careless cut when trimming calluses or corns, or a blister from wearing a new pair of shoes. Most diabetics have altered sensation in their feet due to neuropathy, so even a minor cut or trauma may not produce any pain until the infection becomes apparent (see Fig. 8-1).

Many diabetics neglect corns and calluses because they do not realize the extent of damage these seemingly trivial conditions can cause.

The human body hosts many different kinds of bacteria and fungi, which vary depending on location, environment, and skin condition. For example, the area between the toes harbors a greater number and variety of bacteria than other parts of the body due to moisture, which favors the growth of both bacteria and fungi. Additionally, the feet have lower temperatures compared to other parts of the body, further stimulating the rapid growth of these microorganisms.

It is well known that diabetic feet are more prone to infection. Diabetics do not necessarily have an impaired immune system or altered antibody response when invaded by bacteria, and high blood sugar alone does not generally increase bacterial growth. The exact mechanisms behind the increased severity and frequency of infections in diabetics are not yet fully understood. However, pre-existing circulation problems in the foot, combined with diabetic infections and neuropathy, make infections much more dangerous than in non-diabetic individuals.

In diabetic patients, the progression to a major infection with tissue death can occur much faster, as they may ignore the contagious process due to the absence of pain in neuropathic feet. The small capillary vessels around the infection site may clot, causing further tissue death. Additionally, some bacteria produce toxic substances that exacerbate tissue destruction. When tissue death becomes extensive, the area can become gangrenous. In some cases, the infection may spread to tendons in the foot, and then follow the course of deeper tendons into the leg. This rapid spread of infection poses a serious threat to both life and limb.

SOFT TISSUE INFECTION

Diabetic foot infections can occur in both insulin-dependent and non-insulin-dependent patients, typically in those with foot neuropathy who may not notice early signs of infection due to a lack of pain. Gangrene may develop when toxic substances produced by bacteria lead to inflammation and clot formation in the small arteries, destroying surrounding tissue. Often, these infections produce gas within the soft tissue—an indication of anaerobic bacterial growth—which results in a foul odor. Reduced blood flow from pre-existing circulation problems allows these oxygen-independent bacteria to proliferate, causing extensive tissue destruction. Most diabetic foot infections are polymicrobial, involving a mixture of different bacteria.

Prevention is the best way to manage diabetic foot infections. When you notice even a small cut, callus, or blister, wash the area thoroughly with running water—avoiding strong chemicals like iodine, alcohol, or hydrogen peroxide, which can damage skin cells and exacerbate the risk of infection. Immediately elevate your foot above the level of your heart. If you observe swelling, redness, or a bad odor, contact your doctor right away.

Early treatment is crucial. In the initial stages of infection, your doctor may surgically debride the affected area and drain any pus. A fluid sample is typically sent to the laboratory to identify the bacteria present, which helps in selecting the most effective antibiotic. Because diabetic foot infections are generally polymicrobial, intravenous antibiotics are preferred over oral medications for better coverage. Oral antibiotics may not be sufficient—especially if they target only a single organism like Staphylococcus— because they may not effectively eradicate anaerobic bacteria, and the infection could spread rapidly. In diabetic patients with kidney damage, the antibiotic dose must be carefully adjusted throughout the treatment course to avoid further complications.

Overall, recognizing the early signs of infection and initiating prompt, appropriate treatment is essential to prevent disastrous outcomes such as widespread tissue necrosis, bone infection, and eventual amputation.

BONE INFECTION IN THE DIABETIC FEET

Bone infection, or osteomyelitis, in diabetic feet is one of the most serious complications. Often, this infection—along with a chronic ulcer on the sole of the foot— begins as a callus. In diabetic patients, ulcers on the sole typically take months or even years to heal, if they heal at all. If an ulcer is neglected or does not heal properly, bacteria can invade the ulcer and spread into the deeper tissues of the foot, eventually reaching the bone.

Osteomyelitis is particularly common in diabetic feet affected by neuropathy and poor circulation. Because these patients often experience little or no pain, and because redness and swelling may be absent, a bone infection can go unnoticed until it is quite advanced. Treatment generally involves surgical removal of the infected bone tissue combined with about six weeks of intravenous antibiotics. If these conservative treatments fail, amputation may become necessary.

It is important to note that Charcot's foot—a condition characterized by a red, swollen, and hot foot—can mimic the signs and symptoms of bone infection. Careful examination and diagnostic imaging, such as MRI, are crucial for distinguishing between osteomyelitis and Charcot's foot. I have encountered cases where a diabetic patient underwent amputation under the assumption of a bone infection, only to later find that the patient had the early stage of Charcot's diabetic foot.