What are the skin manifestations of diabetes and how are they managed?

Skin Manifestations of Diabetes and Their Management

Diabetic patients experience a wide range of skin complications, with the most clinically significant being diabetic foot infections, fungal infections (particularly onychomycosis affecting 34% of patients), and various dermatoses, all requiring systematic screening, early recognition, and aggressive multidisciplinary management to prevent limb-threatening complications. 1

Major Skin Manifestations

Diabetic Foot Complications

The diabetic foot represents the most serious skin manifestation, with ulceration occurring as a consequence of diabetic neuropathy and/or peripheral arterial disease (PAD), serving as a major cause of morbidity and disability. 2

• Peripheral neuropathy causes loss of protective sensation, leading to unrecognized trauma and abnormal biomechanical loading that produces callus formation with underlying subcutaneous hemorrhage appearing as brown discoloration 1, 3
• Motor neuropathy creates foot deformities (hammertoes, prominent metatarsal heads, bunions) and abnormal pressure points 1
• Autonomic neuropathy results in dry, cracking skin due to reduced sweating, providing entry points for bacteria 1, 4
• Brown discoloration of feet may represent either subcutaneous hemorrhage from repetitive stress or dependent rubor from critical ischemia—never assume it is benign pigmentation 3

Infectious Complications

Fungal Infections

• Onychomycosis affects approximately 34% of diabetic patients, nearly three times more frequently than non-diabetics, with Trichophyton rubrum being the most common causative agent 1
• Diabetic patients are particularly vulnerable due to reduced peripheral circulation, neuropathy, and impaired wound healing 1
• Untreated fungal nail infections can lead to serious complications including injury to surrounding tissue and increased risk of limb-threatening complications or amputation 1
• Fungal infections of the oral cavity, lower gastrointestinal tract, skin, urogenital system, and blood are also more common in diabetes 5

Bacterial Infections

• Diabetic foot infections typically begin after a break in the protective skin envelope, often at sites of trauma or ulceration 1
• Acute infections in antibiotic-naïve patients are usually monomicrobial, predominantly aerobic gram-positive cocci (Staphylococcus aureus and streptococci) 1, 2
• Chronic wounds develop more complex bacterial flora, including S. aureus, beta-hemolytic streptococci, Enterococci, and various Enterobacteriaceae 1
• Methicillin-resistant S. aureus (MRSA) infections are increasingly common in diabetic patients and are associated with worse outcomes 1, 4

Other Dermatoses

• Necrobiosis lipoidica, granuloma annulare, and acanthosis nigricans are routinely associated with diabetes, especially in patients with chronic disease 6
• The proven link with diabetes varies among these conditions, requiring individual assessment 6

Screening and Prevention

Annual Comprehensive Foot Examination

All patients with diabetes must undergo annual comprehensive foot examination to identify risk factors predictive of ulcers and amputations, using monofilament testing, tuning fork, palpation, and visual examination. 2

Risk Stratification (IWGDF Classification)

• Category 0 (No peripheral neuropathy): Screen once yearly 2
• Category 1 (Peripheral neuropathy): Screen every 6 months 2
• Category 2 (Neuropathy with PAD and/or foot deformity): Screen every 3-6 months 2
• Category 3 (Neuropathy with history of foot ulcer or amputation): Screen every 1-3 months 2

Specific Examination Components

• Use Semmes-Weinstein 5.07 (10-g) monofilament for assessing protective sensation 2
• Use 128-Hz tuning fork for vibration perception 2
• Assess pedal pulses and consider ankle-brachial index (ABI) for PAD screening 2
• Visual inspection should specifically assess for dependent rubor, pallor on elevation, callus formation with brownish discoloration, erythema, warmth, and bony deformities 2, 3

High-Risk Foot Conditions Requiring Increased Surveillance

• Peripheral neuropathy with loss of protective sensation 2
• Evidence of increased pressure (erythema, hemorrhage under callus) 2
• Bony deformity 2
• PAD (decreased or absent pedal pulses) 2
• History of ulcers or amputation 2
• Severe nail pathology 2

Management of Diabetic Foot Infections

Infection Classification and Initial Assessment

Infection should be diagnosed clinically based on the presence of purulent secretions or at least 2 cardinal manifestations of inflammation (redness, warmth, swelling/induration, pain/tenderness)—not all ulcers are infected. 2

Severity Classification

• Mild infection: Cellulitis/erythema extends ≤2 cm around ulcer, limited to skin or superficial subcutaneous tissues, no systemic illness 2
• Moderate infection: Cellulitis extending >2 cm, lymphangitic streaking, deep-tissue abscess, gangrene, or involvement of muscle, tendon, joint, or bone in a systemically well patient 2
• Severe infection: Systemic toxicity or metabolic instability (fever, chills, tachycardia, hypotension, confusion, vomiting, leukocytosis, acidosis, severe hyperglycemia, or azotemia) 2

Microbiological Assessment

• Cleanse and debride the lesion before obtaining specimens for culture 2
• Obtain tissue specimens from the debrided base by curettage or biopsy whenever possible, as these provide more accurate results than superficial swab specimens 2
• Culturing clinically uninfected lesions is unnecessary 2
• Blood cultures should be performed for patients with severe infection, especially if systemically ill 2

Antibiotic Therapy

Mild Infections

• Start empiric oral antibiotic therapy targeted at S. aureus and streptococci 2
• A course of 1-2 weeks is usually adequate for most soft tissue diabetic foot infections 2

Moderate to Severe Infections

• Initiate empiric, parenteral, broad-spectrum antibiotic therapy aimed at common gram-positive and gram-negative bacteria, including anaerobes 2
• Adjust (constrain, if possible) the antibiotic regimen based on clinical response and culture and sensitivity results 2
• Consider MRSA coverage based on patient risk factors and local epidemiology 7
• The highest levels of bacterial resistance are found to beta-lactam antibiotics (amoxicillin/clavulanic acid, ceftriaxone, ampicillin), rifampin, and gentamicin 8
• The highest levels of sensitivity are observed to levofloxacin, vancomycin, and meropenem 8

Surgical Management

• Urgently evaluate for need for surgical intervention to remove necrotic tissue, including infected bone, and drain abscesses in moderate or severe infections 2
• Debride all necrotic tissue and surrounding callus 2
• Surgical procedures must be accompanied by proper wound care, treatment of comorbid conditions, and appropriate revascularization when needed 2

Hospitalization Criteria

Hospitalize patients with severe infections or those complicated by critical limb ischemia. 2 Additional indications include:

• Systemic toxicity (fever, leukocytosis) 2
• Metabolic instability (severe hypoglycemia or acidosis) 2
• Rapidly progressive or deep-tissue infection 2
• Substantial necrosis or gangrene 2
• Critical ischemia 2
• Requirement for urgent diagnostic or therapeutic interventions 2
• Inability to care for self or inadequate home support 2

Vascular Assessment and Management

Initial Screening

• Obtain history for claudication and assess pedal pulses 2
• Consider obtaining ankle-brachial index (ABI), as many patients with PAD are asymptomatic 2
• Normal ABI is >0.9; <0.5 indicates severely impaired circulation; >1.3 suggests calcified vessels from medial arterial sclerosis 3

Critical Ischemia Management

• In patients with ankle pressure <50 mmHg or ABI <0.5, consider urgent vascular imaging and, when appropriate, revascularization 2
• Brown discoloration with absent pedal pulses and dependent rubor requires urgent vascular imaging and consideration for revascularization 3
• Refer patients with significant claudication or positive ABI for further vascular assessment, and consider exercise, medications, and surgical options 2

Local Wound Care

• Inspect the ulcer frequently and debride with scalpel, repeating as needed 2
• Select dressings to control excess exudation and maintain moist environment 2
• Consider negative pressure therapy to help heal post-operative wounds 2
• Consider systemic hyperbaric oxygen treatment in poorly healing wounds 2
• Do not use footbaths in which feet are soaked, as they induce skin maceration 2

Pressure Offloading

• People with neuropathy and evidence of increased plantar pressure may be adequately managed with well-fitted walking shoes or athletic shoes that cushion the feet and redistribute pressure 2
• People with bony deformities (hammertoes, prominent metatarsal heads, bunions) may need custom-molded shoes 2
• Callus can be debrided with a scalpel by a foot care specialist 2

Patient Education

Provide general foot self-care education to all patients with diabetes in several sessions over time, using a mixture of methods. 2

• Instruct patients on how to recognize potential foot problems and steps to take when problems arise 2
• Teach patients to report signs of new or worsening infection (fever, changes in local wound conditions, worsening hyperglycemia) 2
• During enforced bed rest, instruct on preventing ulcers on the contralateral foot 2
• Refer patients who smoke, have loss of protective sensation and structural abnormalities, or have history of prior lower-extremity complications to foot care specialists for ongoing preventive care and life-long surveillance 2

Multidisciplinary Approach

A multidisciplinary approach is recommended for individuals with foot ulcers and high-risk feet, especially those with a history of prior ulcer or amputation. 2

• The team should include diabetologist, surgeon (general, orthopedic, or foot), vascular surgeon, endovascular interventionist, podiatrist, diabetic nurse, shoe-maker, orthotist, or prosthetist 2
• A multidisciplinary approach involving dermatology, infectious disease, and vascular specialists is optimal for managing complex diabetic skin problems 1

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for uninfected ulcerations—available evidence does not support their use to enhance wound healing or as prophylaxis 2
• Never assume brown discoloration is benign—it often represents either subcutaneous hemorrhage or critical ischemia 3
• Peripheral neuropathy may mask typical pain symptoms, delaying recognition of infection 4
• An ABI >1.3 does not rule out vascular disease—it indicates poorly compressible vessels requiring alternative vascular assessment 3
• 50% of patients with limb-threatening infection do not manifest systemic signs or symptoms 2
• Regular foot examination may be challenging due to obesity, retinopathy, or cataracts, but remains essential 1

Glycemic Control

There is a vicious circle in patients with type 2 diabetes: the infectious process leads to decompensation of carbohydrate metabolism; hyperglycemia leads to increased severity of skin and soft tissue infections. 8

• Normalization of glucose levels promotes prompt relief of infection symptoms and bacterial eradication 8
• Rational treatment of infection contributes to rapid correction of glucose levels 8
• High glucose levels play a crucial pathogenetic role in tissue damage and delayed clinical cure 7