--- module: 034-02 language: en chapter: 34 title: "Skin Function, Wounds, Infection, Tumours, and Clinical Examination" module_title: "Barrier failure, lesion morphology, wound physiology, and dermatological emergencies" source_sha256: e320a46df84ccf14377fd477b8bb38d5e878dbc96648fb09e6143d0a290aecd2 --- # Barrier failure, morphology, wounds, emergencies ## Observation before interpretation ### Separate observation from interpretation ### Describe lesion, border, surface, colour, evolution ### Plaque raised and broad; vesicle clear fluid ### Pustule purulent but not necessarily infected ### Secondary changes obscure the initiating lesion #### Early photographs recover lost morphology ### Distribution identifies mechanism #### Sharp exposed pattern: contact or light #### Grouped dermatomal vesicles: zoster #### Advancing annular scale: dermatophyte ### Drug and viral eruptions begin on the trunk #### Mucosa and systemic features set urgency ## Barrier and topical treatment ### Keratinocytes, moisturising factors, organised lipids ### Damage raises transepidermal water loss #### Antigen entry, inflammation, further damage #### Emollients are mechanistic treatment ### Occlusion aids penetration but macerates ### Ointment for dry thick, cream for flexural sites ### Thin skin absorbs more and atrophies ### Specify potency, quantity, duration #### Apply thinly is not a dose: fingertip units ### Failure: review diagnosis, allergy, application ## Inflammatory disease mechanisms ### Atopic dermatitis: interacting links #### Scratching disrupts the stratum corneum #### Weeping alone does not prove infection #### Punched-out erosions: eczema herpeticum ### Psoriasis: accelerated keratinocyte proliferation #### Small area can still carry high burden #### Pustular or erythrodermic: homeostasis fails ### Urticaria: migrating wheals leave normal skin #### Lesions beyond a day suggest vasculitis ### Angioedema: histamine versus bradykinin #### Bradykinin forms lack wheals, resist antihistamines ## Cellulitis and necrotising infection ### Mimics: stasis, lymphoedema, gout, venous thrombosis #### Symmetric erythema without fever: reconsider ### Redness may expand transiently after treatment ### Necrotising infection spreads along fascia #### Early skin findings modest #### Scores and imaging cannot rule it out #### Antibiotics alone cannot reach dead tissue ## Wound healing and chronic wounds ### Overlapping phases, not a rigid sequence ### Platelets, macrophages, fibroblasts coordinate repair ### Persistent inflammation arrests progression ### Treat the cause before dressing brand #### Pulses, perfusion, sensation, oedema, pressure #### Compression can worsen arterial insufficiency #### Off-load painless neuropathic ulcers #### Stable ischaemic heel eschar may protect ### Surface culture may show only colonisers #### Integrate clinical signs to diagnose infection ## Pressure injury ### Deformation, shear, impaired reperfusion ### Deep muscle injured before epidermis ### Repositioning interval is individualised ### Tubing, masks, and devices create focal risk ### Nutrition cannot overcome ongoing pressure ## Burns ### Depth evolves with oedema and hypoperfusion ### Surface area estimate excludes simple erythema ### Electrical injury: deep damage, small wound ### Chemical burns: remove clothing, irrigate long ### Inhalation injury: early airway oedema #### Secure the airway before swelling ### Fluid formula is only a starting estimate #### Under-resuscitation impairs organ perfusion #### Excess fluid worsens oedema, compartment pressure ## Severe drug reactions ### Simple morbilliform: no mucosal or organ injury ### Eosinophilic systemic reaction after latency ### Stevens-Johnson syndrome, toxic epidermal necrolysis #### Withdraw drugs, burn-level supportive care ### Drug timeline up to eruption onset ### Organ injury does not parallel skin area ### Record the specific drug and reaction ## Pigmented lesions and skin of colour ### Prioritise evolution and difference from background ### Nodular lesions uniform but fast-growing ### Amelanotic melanoma pink or red ### Excision biopsy measures Breslow thickness ### Erythema violaceous, grey, or warmth only ### Palpation and comparison with unaffected skin ### Emergencies are physiological ### Supportive care not delayed for results