Delayed Wound Healing in Diabetes Mellitus

Normal Wound Healing: A Brief Overview

1. Hemostasis - platelet aggregation, fibrin clot formation
2. Inflammation - neutrophil and macrophage recruitment, debris clearance
3. Proliferation - fibroblast migration, collagen synthesis, angiogenesis, re-epithelialization
4. Remodeling - collagen cross-linking, scar maturation

Pathogenesis of Delayed Wound Healing in DM

1. Diabetic Neuropathy

• Loss of sweating produces dry, cracked skin that acts as an entry point for bacteria
• Arteriovenous shunting within the skin microcirculation reduces cutaneous perfusion and oxygen saturation
• Contributes to Charcot joint (degenerative arthropathy), further increasing pressure-related ulceration risk - Dermatology 5e, p.2209

2. Vascular Disease (Ischemia)

• Microangiopathy: Basement membrane thickening in capillaries reduces oxygen and nutrient delivery to tissues; this is an early DM complication
• Macroangiopathy (PAD): Atherosclerosis characteristically affects infrapopliteal vessels (below the knee) in diabetics, causing ischemic complications
• The combination of decreased blood supply + mechanical damage produces neuroischemic ulcers
• PAD also impairs the immune response to foot infections, predisposing to cellulitis, abscess, and osteomyelitis - Dermatology 5e

3. Impaired Immune/Inflammatory Response

• Hyperglycemia impairs neutrophil and macrophage function (reduced chemotaxis, phagocytosis, oxidative burst)
• Persistent, dysregulated inflammation prevents transition from the inflammatory phase to the proliferative phase
• Elevated protease activity (MMPs, serine proteases from macrophages/neutrophils) with reduced protease inhibitors degrades growth factors and extracellular matrix, perpetuating a non-healing environment - Dermatology 5e, p.4137

4. Impaired Growth Factor Activity

• Endogenous growth factors (VEGF, PDGF, FGF, TGF-beta) are often degraded or trapped within chronic diabetic wounds
• VEGF production is impaired, leading to reduced angiogenesis
• Hyperglycemia reduces fibroblast proliferation and migration
• Advanced Glycation End-products (AGEs) cross-link collagen, reduce tissue flexibility, and impair normal matrix remodeling

5. Impaired Angiogenesis

• Reduced VEGF and FGF signaling means new blood vessel formation is inadequate
• Tissue hypoxia develops and worsens, further impairing cellular metabolism needed for repair

6. Infection

• Hyperglycemia provides a rich substrate for bacterial growth
• Impaired leukocyte function reduces the ability to clear pathogens
• Polymicrobial infections are common; deep infections (osteomyelitis) dramatically worsen prognosis

Summary Table: Mechanisms

Clinical Features of Diabetic Foot Ulcers

• Located over plantar pressure points (metatarsal heads, heel) or over bony deformities
• Typically well-defined, punched-out borders with surrounding callus (neuropathic ulcer)
• May be painless due to sensory neuropathy
• Can have ischemic features (pale, cold, poorly perfused wound bed) if PAD is dominant
• Probing-to-bone test positive suggests osteomyelitis

Classification (Wagner Scale - Widely Used)

Management Principles

1. Glycemic control - tight control prevents progression of microangiopathy and neuropathy
2. Off-loading - total contact casting is the gold standard; distributes pressure away from ulcer
3. Wound debridement - removes necrotic tissue, biofilm, and excess ECM; liberates trapped growth factors and facilitates cell migration - Dermatology 5e, p.2210
4. Moist wound environment - promotes epithelialization
5. Infection management - culture-guided antibiotics; surgical drainage for abscesses
6. Vascular assessment and revascularization - percutaneous angioplasty or surgical bypass when PAD is present
7. Growth factor therapy - Becaplermin gel (recombinant PDGF-BB, Regranex) is the only FDA-approved topical growth factor for chronic neuropathic diabetic ulcers; shown to increase healing rates and shorten healing time - Dermatology 5e
8. Hyperbaric oxygen therapy (HBO) - specific benefit in diabetic foot ulcers; increases tissue oxygen level, reduces healing time and amputation rate; HBO works by increasing blood oxygen in hypoxic tissue and redistributing flow via hyperoxic vasoconstriction of surrounding normal tissue - Dermatology 5e, p.2019-2020
9. Wound dressings - selection based on wound characteristics (hydrocolloids, foams, silver-containing dressings for infected wounds)

Prevention

• Tight glycemic control (HbA1c targets)
• Regular foot inspection (patient self-exam + clinical exam)
• Protective footwear
• Podiatric care for callus removal and nail care
• Screening and treatment of PAD and neuropathy