Diabetic Foot Infection Signs and Symptoms

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

• The IWGDF categorized the risk of patients w/ diabetes for foot ulceration