48. Atherosclerotic and diabetic gangrene of the limbs

1. Definition

• Gangrene → death of a large area of tissue, with putrefaction
• Atherosclerotic gangrene → tissue death from end-stage arterial occlusion (Fontaine IV, CLTI)
• Diabetic gangrene (diabetic foot) → ulceration, infection or gangrene of the foot in a diabetic, from neuropathy, ischaemia and infection
• Dry gangrene → dry, shrunken, mummified tissue without infection
• Wet gangrene → moist, swollen, infected tissue with spreading putrefaction

2. Epidemiology

• Diabetic foot ulcer → lifetime risk up to 25% in diabetes
• Diabetics are about 15 times more likely to have a major amputation
• 85% of diabetic amputations start with an ulcer
• Diabetic ulcers → 45% neuropathic, 10% ischaemic, 45% mixed neuro-ischaemic
• 5-year mortality after major amputation → about 50–70%

3. Aetiology and risk factors

Atherosclerotic gangrene

• Progressive atherosclerosis → smoking, hypertension, hyperlipidaemia, age
• Acute thrombosis on a plaque, embolism
• Minor trauma on an ischaemic foot (tight shoes, nail cutting)

Diabetic foot

• Neuropathy:
  • Sensory → painless injury not noticed
  • Motor → clawed toes, high pressure under metatarsal heads
  • Autonomic → dry, cracked skin; arteriovenous shunting
• Ischaemia → diffuse, distal (tibial) disease; calcified arteries (Mönckeberg's sclerosis)
• Infection → poor immunity from high glucose
• Previous ulcer or amputation, deformity, Charcot foot, callus
• Poor glucose control, kidney failure, poor vision, living alone
• Organisms → S. aureus, streptococci, Gram-negatives, anaerobes (often mixed)

4. Pathogenesis

Dry gangrene

1. Slow fall in arterial flow
2. Tissue dies and dries out → coagulative necrosis
3. Haemoglobin breaks down → black colour (iron sulphide)
4. Line of demarcation forms → band of granulation tissue between dead and living tissue
5. Dead part may separate on its own (autoamputation)

Wet gangrene

1. Fast ischaemia, venous congestion and infection
2. Liquefactive necrosis, putrefaction by bacteria
3. No clear demarcation → spreads quickly
4. Toxins absorbed → sepsis
5. Gas gangrene → Clostridium; crepitus; surgical emergency

Diabetic foot

• Neuropathy → unnoticed injury → ulcer
• Ischaemia → poor healing
• Infection → spreads along tendon sheaths and plantar spaces → abscess, osteomyelitis, wet gangrene
• Charcot foot → neuropathic joint destruction; "rocker-bottom" deformity

5. Classification

By type

• Dry → atherosclerotic, embolic, Buerger's
• Wet → diabetic, venous obstruction, infected dry gangrene
• Gas gangrene (Clostridium)

Wagner (diabetic foot)

• 0 → no ulcer, foot at risk (deformity, callus)
• 1 → superficial ulcer
• 2 → deep ulcer to tendon, capsule or bone
• 3 → deep ulcer with abscess or osteomyelitis
• 4 → forefoot gangrene
• 5 → whole-foot gangrene

Others

• University of Texas → depth plus infection and ischaemia
• WIfI → wound, ischaemia, foot infection

6. Clinical picture

Symptoms

• Atherosclerotic → claudication, then rest pain, then black toes
• Diabetic neuropathic → painless ulcer, numb "stocking" feet
• Wet gangrene → swelling, smell, discharge, fever, confusion (sepsis)

Signs

• Dry gangrene:
  • Black, dry, shrunken, cold
  • Clear line of demarcation
  • No pulse, no sensation, no capillary refill
• Wet gangrene:
  • Swollen, blistered, discoloured, foul-smelling
  • Cellulitis spreading up the leg, lymphangitis
  • Crepitus → gas-forming organisms
• Neuropathic ulcer → warm foot, palpable pulses, painless, under the metatarsal head or heel, surrounded by callus
• Ischaemic ulcer → cold foot, absent pulses, painful, on toes, heel, edges of the foot
• Probe-to-bone test → positive suggests osteomyelitis
• Sensation → 10 g monofilament, vibration (128 Hz tuning fork)

7. Diagnosis

Laboratory

• FBC, CRP, ESR, glucose, HbA1c, U&E (kidney function), lactate
• Blood cultures, deep tissue or bone culture (not surface swabs)

Vascular assessment

• Pulses, ABPI → falsely high in diabetics (calcification)
• Toe pressures, toe-brachial index, transcutaneous oxygen (TcPO₂)
• Duplex ultrasound, CT or MR angiography, digital subtraction angiography → plan revascularisation

Imaging of the foot

• Plain X-ray → gas in tissues, osteomyelitis, Charcot changes, foreign body
• MRI → osteomyelitis, abscess, extent of infection
• Bone scan, white cell scan

8. Differential diagnosis

• Neuropathic versus ischaemic versus venous ulcer
• Necrotising fasciitis
• Cellulitis without gangrene
• Charcot foot versus osteomyelitis
• Frostbite, Buerger's disease, vasculitis
• Embolic "blue toe" syndrome

9. Treatment

• Team → multidisciplinary diabetic foot team: vascular surgeon, diabetologist, podiatrist, orthotist, microbiologist, nurses

Conservative

• Prevention:
  • Daily foot inspection, proper footwear, never walk barefoot
  • Podiatry → callus and nail care
  • Annual foot screening
• Glucose control, stop smoking, statin, antiplatelet
• Offloading → total contact cast, removable boot, bed rest
• Antibiotics → broad-spectrum IV for severe infection, then culture-guided; 6 weeks for osteomyelitis
• Wound care → moist dressings, negative pressure therapy
• Dry gangrene → keep dry and cool; never heat the limb; wait for demarcation if no infection

Surgical

• Wet gangrene or abscess → urgent debridement and drainage; open all infected spaces; remove dead tissue and bone
• Revascularisation → for ischaemic or mixed ulcers:
  • Angioplasty (tibial arteries)
  • Femorodistal bypass with vein
  • Do it before or soon after debridement, so wounds can heal
• Amputation → at the lowest level that will heal:
  • Toe, ray, transmetatarsal → diabetic forefoot disease
  • Below-knee (long posterior or skew flap; tibia cut 10–15 cm below the knee joint) → best for walking with a prosthesis
  • Above-knee → non-ambulant, failed below-knee, poor blood flow at the knee
  • Guillotine amputation → life-threatening sepsis; formal stump 2–5 days later
• Wound cover → skin graft, flaps

10. Complications

• Sepsis, death
• Osteomyelitis
• Major amputation, amputation of the other leg (50% within 5 years)
• Stump problems → infection, failure to heal, re-amputation, phantom limb pain, contracture
• Cardiovascular death
• Recurrence of ulcers (up to 40% in 1 year)