Approach to skin conditions

Table of Contents

History

Chief complaint
Discomfort, duration, rate of progression and location
Secondary history:
- Systemic complaints
- Mucosal involvement
- Exposures to medicines, immunisations, chemicals, food, animals, insects, pets, plants, sunlight and sick contacts
- Sexual history
PMHx and FHx

Distribution

Flexor: Atopic dermatitis, candidiasis, eczema, ichthyosis (rare genetic thickened scaly skin)
Sun exposure: Sunburn, photosensitive drug eruption, photosensitive dermatitis, SLE, viral exanthem, porphyria
Distal extremities: Viral exanthem, atopic or contact dermatitis, eczema, gonococcaemia
Front and back of chest: Pityriasis rosea, secondary syphilis, drug eruption, atopic or contact dermatitis, psoriasis
Clothing covered: Contact dermatitis, psoriasis, folliculitis
Acneiform: Acne, drug-induced acne, irritant dermatitides

Configuration

The primary lesion

One that has not been altered by healing, treatment, complicating infection or scratching
Primary skin lesions are macules, papules, nodules, tumors, cysts, plaques, wheals, vesicles, bullae and pustules
Secondary skin lesions have been altered and are described as crusts, scales, fissures, erosions, ulcerations, excoriations, atrophy, scarring and lichenification
Papule <0.5cm (larger = nodule)
Vesicle < 5mm

DDx based on primary lesion morphology

Macule: Drug eruption, nevus, tattoo, rheumatic fever, secondary syphilis, viral exanthem, meningococcaemia (early), ecchymosis, vitiligo, tinea versicolor, cellulitis (early)
Papule: Acne, BCC, melanoma, nevus, warts, molluscum contagiosum, skin tags, atopic dermatitis, urticaria, eczema, folliculitis, insect bite, vasculitis, psoriasis, scabies, erythema multiforme, early varicella, gonococcaemia

DDx primary morphology

Plaque: Eczema, pityriasis rosea, tinea corporis, tinea versicolor, psoriasis, seborrhoeic dermatitis, urticaria, secondary syphilis, erythema multiforme
Nodule: BCC, SCC, metastatic carcinoma, melanoma, erythema nodosum, furuncle, lipoma, warts
Wheal: Urticaria, angioedema, insect bite, erythema multiforme
Pustule: Acne, gonococcaemia, folliculitis, hidradenitis suppurativa, herpes, impetigo, psoriasis, rosacea, pyoderma gangrenosum

DDx primary morphology

Vesicle: Herpes, impetigo, thermal burn, friction blister, toxic epidermal necrolysis, bullous pemphigoid, pemphigus vulgaris
Bulla: Bullous pemphigoid, thermal burn, friction burn, TEN/SJS, bullous impetigo, pemphigus vulgaris

DDx secondary morphology

Scales: Psoriasis, pityriasis rosea, eczema, secondary syphilis, tinea, tinea versicolor, xerosis, thermal burn
Crusts: Eczema, tinea, impetigo, contact dermatitis, insect bite
Erosions: Candidiasis, tinea, eczema, TEN, erythema multiforme, bullous pemphigoid, pemphigus vulgaris
Ulcers: Aphthous, chancroid, decubitus ulcer, thermal or friction injury, ischaemic, malignancy, primary syphilis chancre, bullous pemphigoid, pemphigus vulgaris, pyoderma gangrenosum, stasis ulcer

Three concentric colour zones
- Dark central blister
- Ring of paler pink and raised
- Bright red outer ring
Can arise anywhere
Iris lesion is an early target lesion with only central dusky zone and red outer zone
Single component red plaques are also seen in erythema multiforme
Atypical target lesions have just two zones or indistinct border
- In EM they are raised while in SJS/TEN they are flat
DDx
- Erythema multiforme
- Stevens-Johnson syndrome
- TEN

Exanthematous
- Morbilliform, scarlatiniform or confluent erythematous patches
- Mostly seen with EBV, HIV, leukaemia and concomitant allopurinol use
DRESS
- Drug reactions with eosinophilia and systemic symptoms
- Aka drug hypersensitivity syndrome with fever, malaise, lymphadenopathy and skin eruptions
- Usually 2-6 weeks after initiation
- Severe reaction seen with phenytoin, carbamazepine, lamotrigine, phenobarbitone, allopurinol and sulfas
- Associated with exfoliative dermatitis, hepatitis, pneumonitis and renal impairment

Drug-induced urticaria/angioedema
- Angioedema and wheal/flare within 3 weeks of exposure
- May be IgE mediated type I hypersensitivity (esp. antibiotics) or mast-cell degranulation not by IgE-mediated process (e.g. opioids, vancomycin red man)
Fixed-drug eruption
- Solitary or multiple oval plaques +- central blisters with dark postinflammatory pigmentation
- Reoccur at same sites with re-exposure
- Typically lips, tongue, genitalia, face and acral regions
- NSAID’s, bactrim, doxycycline, penicillins, quinolones, barbiturates, paracetamol and antimalarials

Drug-induced photosensitivity
- Immunological (e.g. photoallergic) – UV-A converts drug into immunologically active compound leading to eczema. Seen with topical soaps, fragrances, chlorpromazine, sulfas and NSAID’s + quinine
- Toxicological (e.g. phototoxic) – Drug absorbs UV-A and releases energy causing inflammation. Presents as exaggerated sunburn with blistering. Seen with NSAID’s, doxycycline, ciprofloxacin, amiodarone and chlorpromazine
Drug-induced pigmentation
Cutaneous small vessel vasculitis (aka serum sickness)
- Single organ vasculitis
- Hydralazine, propylthiouracil most often
- Antibiotics and sulfas also seen
- Palpable purpura, petechiae, fever, arthralgias, lymphadenopathy, low serum complement levels and raised ESR.
- Usually 7-10 days after exposure

Exfoliative dermatitis/erythroderma
- Chronic erythema and scale >90% BSA
- Seen with allopurinol, penicillins, phenobarbitone
SJS/TEN
Anaphylaxis
Erythema multiforme
- Typically infection-driven but has been seen with anticonvulsants, penicillins

Type I – IgE mediated
Type II – Cytotoxic. Antibody-dependent. Complement. E.g. Goodpastures, Myaesthenia gravis, autoimmune haemolytic anaemia
Type III – Immune complex. Serum sickness, RA
Type IV – Delayed-type. Cell-mediated. Contact dermatitis, Mantoux test

Last Updated on October 13, 2021 by Andrew Crofton