diabetic%20foot%20infection
DIABETIC FOOT INFECTION

Diabetic foot infection occurs in patients with diabetes as they are prone to microorganism invasion and multiplication in the soft tissue or bone (anywhere below the malleoli) that leads to host inflammatory response that usually results to tissue destruction.

Staphylococci and streptococci are the most common causative organisms although most diabetic foot infections are polymicrobial.

Most infections usually start with a break in the protective cutaneous envelope of the skin that resulted from trauma or neuropathic ulceration.

Management of diabetic foot ulcer in patients with diabetes needs an interdisciplinary approach to address glycemic control, infection, offloading of high-pressure areas, lower extremity vascular status and local wound care.

Introduction

  • Patients w/ diabetes are prone to have invasion & multiplication of microorganisms in the soft tissue or bone (anywhere below the malleoli) called diabetic foot infection that leads to host inflammatory response that usually results to tissue destruction

Epidemiology

  • Based on 2015 prevalence data from the International Diabetes Federation, foot ulcers develop annually in 9.1 to 26.1 million people w/ diabetes worldwide
  • An estimated 10% of patients w/ diabetes will have diabetic foot ulcer that precedes more than 80% of non-traumatic amputations
  • Lifetime risk of developing a foot ulcer in patients w/ diabetes is 15-25% before but additional data showed between 19% & 34% of persons w/ diabetes will likely to be affected
  • Foot infection is very common in patients w/ diabetes, associated w/ the duration of the disease & likelihood of diabetic complications
  • Infection of the foot is the most common diabetic complication that would require hospitalization

Etiology

  • Staphylococci & streptococci are the most common causative organisms although most diabetic foot infections are polymicrobial
  • Copathogens in chronic infections are aerobic Gram-negative bacilli while obligate anaerobes are copathogens in ischemic or necrotic wounds

Pathophysiology

  • Most infections typically start w/ a break in the protective cutaneous envelope of the skin that resulted from trauma or neuropathic ulceration
  • These open wounds will eventually be colonized by skin flora that in many cases result to infection
    • Due to hyperglycemia-induced advanced glycation end-products, persistent inflammation & apoptosis the wounds in the feet of patients w/ diabetes become chronic
  • The following factors predispose the patient w/ diabetes to have foot infection:
    • Deep wound that is long-standing or recurrent or caused by trauma
    • Ill-defined diabetes-related immunological perturbations related to neutrophil function
    • Chronic renal failure
  • Spread of infection
    • Microorganisms spread proximally to the subcutaneous tissues including fascia, tendons, muscles, joints & bone
      • This is due to the anatomy of the foot which is divided into several rigid but intercommunicating compartments
    • The infection induces inflammatory response that causes compartmental pressure to exceed capillary pressure, resulting to ischemic tissue necrosis
    • The tendons within the compartments cause proximal spread of infection that usually moves from higher to lower-pressure areas
    • Bacterial virulence may play a role in these complex infections
      • Isolate strains of Staphylococcus aureus from clinically non-infected ulcers have been shown to have a lower virulence potential than those that are infected

Signs and Symptoms

  • It is not common in patients w/ diabetic foot infection to have systemic symptoms (eg fever & chills), marked leukocytosis or major metabolic disturbance but its presence will indicate a more severe, potentially limb or even life-threatening infection
  • Patient may also present w/ symptoms of vascular disease (eg claudication, leg fatigue) & neuropathy (numbness, burning, pain)

Risk Factors

  • Patients w/ diabetes who have the following characteristics are predisposed to foot ulcer that leads to infection & ultimately lower extremity amputation:
    • Repetitive stress over an area that is subject to high vertical or shear stress in patients w/ peripheral neuropathy
    • Impaired immunity
    • Peripheral artery disease (PAD)
    • Positive probe-to-bone test
    • Presence of foot ulcer for >30 days
    • Foot wound that is traumatic
    • Previous ulceration or amputation
    • Structural deformity
    • Limited joint mobility
    • Renal insufficiency
    • History of walking barefoot
    • Microvascular complications, peripheral neuropathy with loss of protective sensation (LOPS)
    • High levels of hemoglobin A1c
    • Onychomycosis
    • Visual impairment  
    • Preulcerative corn or callus  
    • Cigarette smoking
International Working Group on the Diabetic Foot (IWGDF) Risk Classification System
  • The IWGDF categorized the risk of patients w/ diabetes for foot ulceration
Category Ulcer Risk Characteristics
0 Very low LOPS and PAD absent
1 Low LOPS or PAD present
2 Moderate LOPS and PAD or
LOPS and foot deformity or
PAD and foot deformity
3 High LOPS or PAD plus ≥1 of the following:
-  History of foot ulcer
-  Lower extremity amputation
-  End-stage renal disease
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