Diabetic%20foot%20infection Diagnosis

Diabetic Foot Soft Tissue Infection

Clinical Findings

• Clinical findings of local & systemic signs & symptoms of inflammation or purulence is essential in the diagnosis of diabetic foot infection
  • Inflammation is the presence of redness (erythema or rubor), warmth (calor), pain or tenderness (dolor), induration (swelling or tumor)

• Patients w/ diabetes presenting w/ wound in the foot should be evaluated at 3 levels:
  • The patient as a whole (eg cognitive, metabolic, fluid status)
  • The affected foot or limb (eg presence of neuropathy, vascular insufficiency)
  • The infected wound

• If signs of local & systemic infection are diminished, the following secondary features can be taken into consideration:
  • Presence of necrosis
  • Friable or discolored granulation tissue
  • Non-purulent secretions
  • Fetid odor
  • Failure of a properly treated wound to heal

• Signs & symptoms of arterial ischemia, venous insufficiency, presence of protective sensation, & biomechanical problems should also be assessed

Diabetic Foot Osteomyelitis

• Diabetic foot osteomyelitis is suspected when the clinician found an ulcer that lies over a bony prominence especially when it does not heal despite adequate off-loading or when the toe looks erythematous & indurated (“sausage toe”)
• Clinical presentation varies w/ site involved, the extent of infected & dead bone, the presence of any associated abscesses or soft tissue involvement, the causative organism(s) & the adequacy of limb perfusion

• Inquire about the following: Previous history of angioplasty or vascular surgery, renal disease, retinopathy, history of ulceration or amputation, Charcot foot, & smoking history

Diabetic Foot Soft Tissue Infection

• Inspect the skin & palpate leg & feet pulses, check for foot deformities, & assess patient neurologically with a 10-g monofilament test along w/ either pinprick, vibration or temperature assessment
  • Ankle-brachial pressure index should be obtained in patients with signs & symptoms of vascular disease
• Skin temperature of the foot, assessed as warmth, is the first indication of inflammation in an insensate foot & may be the first sign of acute Charcot neuroarthropathy resulting from the loss of protective sensation in the foot

Diabetic Foot Osteomyelitis

• Foot ulcers that have the following characteristics are suspected to have diabetic foot osteomyelitis:
  
  • Large (>2 cm) or deep (>3 mm), or that overlay a bony prominence
  • Chronic that do not heal even w/ appropriate wound care
  • Visible or palpable on probing

Diabetic Foot Soft Tissue Infection

Lab Findings

• Leukocytosis & elevated erythrocyte sedimentation rate are highly suggestive of a diabetic foot infection, but their absence does not rule it out

Histological & Microbiological Examinations

• Positive results on both histological & microbiological examinations are essential in the diagnosis of bone infection
• An aseptically obtained bone sample from the base of the debrided wound is used for microbiological examination
  
  • A deep swab can be done if bone sample cannot be obtained

• Results of microbiological & histological examination may provide useful information on the choice of antibiotic treatment
• To determine the causative organisms & antibiotic sensitivities, wound cultures are done
• During evaluation, wounds should be inspected carefully, debrided of devitalized & necrotic tissue, & probed
  
  • Cultures of superficial swabs are discouraged because these often yield contaminants
  • Curettage from the base of an appropriately debrided ulcer or deep tissue specimens obtained by biopsy yield true pathogens & more accurate results

Diabetic Foot Osteomyelitis

Probe-to-Bone Test

• Performed in an infected wound as it is a useful clinical diagnostic tool in diagnosing diabetes foot osteomyelitis when done correctly & interpreted appropriately
• When the blunt sterile metal probe gently inserted through a wound strikes bone (detected by its hard, gritty feel), it denotes positive result that has a high likelihood for diagnosis of diabetic foot osteomyelitis
• A negative test in a patient who has low risk for osteomyelitis likely rules out the diagnosis

Bone Biopsy

• A definite diagnosis of osteomyelitis requires both the presence of histological findings consistent w/ bone infection & the isolation of bacteria from aseptically obtained bone sample
• During a surgical intervention or by percutaneous biopsy, a bone sample is obtained
  
  • Specimen is obtained by going through intact uninfected skin

• In cases of negative culture or one growing only commensal skin flora, it is helpful to have histological examination of bone specimens in interpreting the results of culture
• Bone specimens are processed for both culture & histopathology
• Infected bone usually has inflammatory cells (granulocytes early & mononuclear cells later), while the histomorphology of uninfected bone is normal in diabetic patients, including those w/ neuropathy or peripheral arterial disease
• It is not advised to use results of soft tissue or sinus tract specimens for selecting antibiotic therapy for osteomyelitis as they do not accurately reflect bone culture results
• Bone culture is not always needed when diabetic foot osteomyelitis is suspected, but clinicians should consider this procedure when diagnosis of osteomyelitis remains uncertain despite clinical & imaging evaluations, in cases where data from soft tissue cultures are non-informative, when the infection has failed to respond to initial empiric antibiotic therapy or when considering an antibiotic regimen w/ a higher potential for selecting resistant organisms

Blood Tests

• A highly elevated erythrocyte sedimentation rate increases the likelihood of having diabetic foot osteomyelitis
• C-reactive protein, procalcitonin or blood leukocyte count may be suggestive of diabetic foot osteomyelitis
• A combination of laboratory & clinical findings improves the diagnostic accuracy for diabetic foot osteomyelitis
• Infectious Diseases Society of America (IDSA) had suggested to do PTB test for any diabetic foot infection w/ an open wound to help diagnose or exclude diabetic foot osteomyelitis

Diabetic Foot Osteomyelitis

Imaging Studies

• Plain radiographs show bony changes w/ presence of gas in the soft tissues or radiopaque foreign bodies in patients w/ diabetic foot osteomyelitis
  
  • It has low sensitivity & specificity in differentiating osteomyelitis from Charcot changes

• MRI is used when a diagnosis of diabetic foot osteomyelitis is still uncertain & there is a suspicion of soft tissue abscess
  
  • MRI findings of low focal signal intensity on T1-weighted images, high focal signal on T2-weighted images & high bone marrow signal in short tau inversion recovery sequences are suggestive of diabetic foot osteomyelitis
  • Consider a white blood cell-labelled radionuclide scan or possibly SPECT/CT or 18 F-FDG PET scan when MRI is not available or contraindicated

• The main problems in diagnosing osteomyelitis are that there is a delay in the ability to detect bony changes in early infection on plain radiographs, while later when bony changes occur, it may be difficult to distinguish on imaging studies from those related to Charcot neuroosteoarthropathy
  
  • Long-standing diabetic foot infections or ulcers are more likely to show underlying bony abnormalities because it takes weeks for bone infection to become radiographically apparent

• Identifying the severity of infection guides the clinician w/ the choice & route of administration of empiric antibiotic regimen, helps to determine the indication for hospitalization, the potential necessity & time of foot surgery & the likelihood of having an amputation
• In classifying foot infection, the following should be considered:
  
  • Depth & extent of the tissues involved at initial evaluation
  • Adequacy of arterial perfusion & the possible need for revascularization
  • Systemic toxicity

• The Infectious Diseases Society of America (IDSA) & International Working Group on the Diabetic Foot (IWGDF) classification of diabetic infection (2012):
  
  • Uninfected - No signs of infection or no systemic or local symptoms
  • Infected (Mild) - superficial & limited in size & depth:
    
    • Presence of at least 2 of the following:
      
      • Local swelling or induration
      • Erythema >0.5-≤2 cm around the wound
      • Local tenderness or pain
      • Local warmth
      • Purulent discharge
  • Other causes of skin inflammatory response have been excluded
    
    • Infection involves only the skin & subcutaneous tissues
    • No signs or symptoms of systemic infection
  • Infected (Moderate) - deeper or more extensive
    
    • Infection involves structures deeper than the skin & subcutaneous tissues (eg bone, joint, tendon, muscle)
    • Erythema >2 cm around the wound
    • No signs or symptoms of systemic infection
  • Infected (Severe) - accompanied by systemic signs or metabolic perturbations
    
    • Presence of systemic inflammatory response syndrome as manifested by at least 2 of the following:
      
      • Temperature >38°C or <36°C
      • Heart rate >90 beats/minute
      • Respiratory rate >20 breaths/minute or PaCO₂ < 4.3 kPa
      • White blood cell count >12,000 or <4,000/mm³ or >10% immature forms

• Diabetic foot ulcers can also be classified using the Wagner Diabetic Foot Ulcer Classification system that is based on the depth of penetration, the presence of osteomyelitis or gangrene & the extent of tissue necrosis:
  
  • Grade 0 - Absence of open lesions or ulcer but may have deformity or cellulitis
  • Grade 1 - Diabetic ulcer that is superficial (partial or full thickness)
  • Grade 2 - Ulcer is extended to the ligament, tendon, joint capsule, or deep fascia w/ no abscess or osteomyelitis
  • Grade 3 - Ulcer is deep w/ abscess, osteomyelitis or joint sepsis
  • Grade 4 - Presence of gangrene localized to portion of forefoot or heel
  • Grade 5 - There is extensive gangrene that involves the entire foot

• One of the widely used classification in clinical trials & diabetic foot centers is the University of Texas Wound Classification which assesses wound depth, presence of infection & clinical signs of extremity ischemia:

	Grade 0	Grade 1	Grade 2	Grade 3
Stage A	Completely epithelialized preulcerative or postulcerative lesion	Wound is superficial that does not involve bone, capsule or tendon	Wound that penetrates the tendon or capsule	Wound that penetrates the bone or joint
Stage B	Presence of infection
Stage C	Presence of ischemia
Stage D	Presence of both infection & ishcemia

• Increase in wound grade & stage is less likely to heal without revascularization or amputation 
• To accurately assess a diabetic foot wound, it usually needs to be debrided of any callus & necrotic tissue to fully visualize the wound
• Findings that suggest serious diabetic foot infection & potential indications for hospitalization:
  
  • Wound that penetrates to subcutaneous tissue w/ cellulitis that is extensive (>2 cm), distant from ulceration or rapidly progressive
  • Wound has severe inflammation or induration, crepitus, bullae, discoloration, necrosis or gangrene, ecchymoses or petechiae, new anesthesia
  • Infection presents as acute onset/worsening or rapidly progressive
  • Presence of fever, chills, hypotension, confusion, volume depletion
  • Laboratory findings of leukocytosis, elevated C-reactive protein or erythrocyte sedimentation rate, severe/worsening hyperglycemia, acidosis, new/worsening azotemia, electrolyte abnormalities
  • Presence of a foreign body (accidental or surgically implanted), puncture wound, deep abscess, arterial or venous insufficiency, lymphedema, immunosuppressive illness or treatment
  • There is still infection progression while on apparently appropriate antibiotic & supportive therapy

• Findings that suggest hospitalization is indicated:
  
  • Severe infection
  • Metabolic or hemodynamic instability
  • Intravenous therapy needed
  • Diagnostic testings needed that are not available as outpatient
  • Presence of critical foot ischemia (it may indicate diminishing clinical findings & worsening prognosis)
  • Failure of outpatient management
  • Surgical procedures (more than minor) required
  • Patient is noncompliant w/ outpatient-based treatment
  • Need for more complex dressing changes than patient/caregivers can provide
  • Need for careful continuous observation

Diabetic Foot Osteomyelitis

• Serious complication of diabetic foot infection that is found in approximately 50-60% of patients hospitalized w/ diabetic foot infection & approximately 10-20% of apparently less severe infections in the ambulatory setting
• It is the infection of the bone of the forefoot & develops by contiguous spread from overlying soft tissue, penetration through the cortical bone & into the medullary cavity