5.6 Dermatologic Examination: Diabetic Dermatoses and Nail Disorders

A Reproducible Skin Survey

Inspect both lower legs, ankles, dorsal and plantar feet, heels, interdigital spaces, and every nail under good light. Compare sides for color and temperature. Describe texture, hair distribution, moisture, turgor, edema, scaling, maceration, fissures, scars, callus, hemorrhage, blisters, erosions, ulcers, and drainage. Palpate cautiously for warmth, induration, fluctuance, tenderness, and crepitus when indicated. Temperature or color differences are clues, not stand-alone diagnoses.

Xerosis and fissuring commonly accompany autonomic neuropathy and environmental dryness. Fissures can become portals of entry, especially at the heel. Interdigital maceration suggests excess moisture and may coexist with tinea or bacterial overgrowth. Emollient may be used on dry intact skin but is generally kept out of the web spaces. Thick waxy skin and limited joint mobility may reflect glycation-related connective-tissue change, while edema can reflect venous, cardiac, renal, medication, inflammatory, or dependent causes.

Callus indicates repeated load or shear. A sharply localized callus over a prominence is a map of mechanical stress. Subcallous hemorrhage—dark red or brown discoloration within callus—may represent tissue injury beneath an intact surface and is treated as pre-ulcerative. Qualified removal can reveal the true condition, but the plan must also offload the site and correct footwear or biomechanical causes. Corns between or over toes similarly indicate focal pressure.

Recognizing Common Diabetic Dermatoses

Diabetic dermopathy usually appears as multiple small, round or oval, light-brown atrophic macules on the shins. Lesions are often asymptomatic and require no wound treatment, but the pattern can accompany long-standing microvascular complications. An inflamed, ulcerated, painful, or rapidly changing lesion should not be dismissed as dermopathy.

Necrobiosis lipoidica often presents on the pretibial legs as yellow-brown atrophic plaques with a violaceous raised border and visible superficial vessels. It may ulcerate after trauma. Avoid assuming every pretibial plaque is diabetic in origin; atypical morphology or diagnostic uncertainty warrants dermatology assessment, and ulceration requires protection and wound evaluation.

Bullosis diabeticorum consists of spontaneous, usually painless, tense bullae on otherwise noninflamed acral skin. The blister roof is protective when intact. The clinician excludes friction, burns, edema bullae, autoimmune blistering disease, and infection; protects the area; and monitors closely. Aspiration or other intervention, when clinically needed, preserves the roof and uses appropriate technique. Erythema, purulence, systemic illness, or necrosis points away from a simple uncomplicated bulla.

Granuloma annulare commonly forms smooth, firm papules arranged in annular plaques, often on hands or feet. It generally lacks scale. Widespread or atypical disease may prompt medical assessment, but it is not itself a diabetic foot ulcer. Tinea often has scale and an advancing border; interdigital tinea may fissure and increase bacterial-entry risk.

Nail Examination

Describe each nail’s color, thickness, contour, surface, attachment, subungual material, and surrounding folds. Onychauxis is thickening; onychogryphosis includes marked curvature; onychocryptosis is an ingrowing margin; paronychia is inflammation of the fold. Onychomycosis may produce yellow-white discoloration, crumbling, subungual debris, and separation, but trauma and inflammatory disease can mimic it. Confirmatory testing is appropriate before prolonged systemic antifungal therapy when the diagnosis is uncertain.

Nail disease matters mechanically. A thick plate can strike the toe box, a curved edge can penetrate the fold, and a rough nail can abrade an adjacent insensate toe. Look for a matching pressure mark in the shoe. Drainage, spreading erythema, fluctuance, ulcer beneath the nail, or a sausage-like toe requires infection and depth assessment. A new irregular pigmented band, pigment involving adjacent skin, or a changing subungual lesion needs prompt specialist evaluation rather than presumptive treatment as fungus or hematoma.

Color, Perfusion, and Escalation

Pallor on elevation, dependent rubor, cyanosis, coolness, delayed capillary refill, absent pulses, or tissue loss can support ischemic concern, but no bedside skin sign alone excludes or confirms PAD. Objective vascular testing is needed when the wound, history, or examination warrants it. Erythema may reflect infection, pressure, venous inflammation, gout, dermatitis, or active Charcot disease; distribution, warmth, wound findings, systemic state, and imaging or laboratory workup distinguish them.

Record what is seen before naming it: “1.2-cm tense clear bulla on nonerythematous dorsal second toe” is more useful than “diabetic blister.” Measurements, photographs with consent and scale, and serial comparison show trajectory. Urgent escalation is appropriate for rapidly spreading erythema, systemic toxicity, wet gangrene, crepitus, fluctuance, new necrosis, severe ischemia, or a hot swollen neuropathic foot requiring Charcot evaluation.

Morphology Guide