Psoriasis

Clinical features

•    Chronic, relapsing-remitting inflammatory disease

•    Well-demarcated erythematous plaques with silvery scale

•    Distribution:

o    Extensor surfaces (elbows, knees)

o    Scalp, sacrum

•    Nail changes:

o    Pitting

o    Onycholysis (separation of nail from bed)

o    "Oil drop" discolouration

Systemic associations

•    Psoriatic arthritis: can present with dactylitis ("sausage digits"), enthesitis

•    Increased cardiovascular risk

Triggers

•    Trauma (Koebner phenomenon)

•    Stress

•    Infection (e.g., streptococcal pharyngitis in guttate psoriasis)

•    Medications: lithium, beta-blockers, antimalarials, NSAIDs

Treatment

•    Topical: emollients, steroids, vitamin D analogues (e.g., calcipotriol)

•    Severe cases: phototherapy (NB-UVB), systemic (methotrexate, ciclosporin, biologics)

Eczema (Dermatitis)

Types

Atopic dermatitis

•    Common in childhood, often improves with age

•    Flexural distribution in older children/adults

•    Associated with atopy: asthma, allergic rhinitis

•    Features: pruritus, lichenification (chronic), secondary infection (impetiginisation)

Contact dermatitis

•    Allergic: type IV hypersensitivity

o    Nickel, fragrances, cosmetics

•    Irritant: most common type

o    Soaps, detergents

Seborrhoeic dermatitis

•    Affects sebaceous areas: scalp (dandruff), eyebrows, nasolabial folds, retroauricular

•    Associated with Malassezia (Pityrosporum) yeast

•    Common in Parkinson's disease and HIV

Treatment

•    Emollients, topical steroids

•    Calcineurin inhibitors (e.g., tacrolimus) for sensitive areas

•    Antifungals for seborrhoeic subtype

Lichen Planus

Features

•    Pruritic, purple, polygonal, planar papules and plaques (6 Ps)

•    Distribution: flexor surfaces (wrists), shins, mucous membranes

•    Oral lesions: lacy white lines (Wickham striae)

Associations

•    Hepatitis C

•    Drug-induced (e.g., gold, thiazides)

Treatment

•    Topical steroids

•    Systemic therapy for severe cases

Erythema Multiforme

Features

•    Target lesions: concentric rings with central dusky area

•    Symmetrical, often acral (hands, feet)

Causes

•    Infections:

o    HSV (most common)

o    Mycoplasma pneumoniae

•    Drugs: sulfonamides, penicillins, anticonvulsants, NSAIDs

Note

•    Severe forms: Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis (TEN)

Erythema Nodosum

Features

•    Tender, erythematous subcutaneous nodules, usually on shins

•    Often migratory and bilateral

Causes

•    Systemic infections: streptococcus, TB, yersinia

•    Granulomatous diseases: sarcoidosis

•    IBD: Crohn’s, ulcerative colitis

•    Medications: sulfonamides, oral contraceptives

Treatment

•    Underlying cause

•    NSAIDs for pain

Other Relevant Conditions

Pityriasis rosea

•    Herald patch → "Christmas tree" distribution on trunk

•    Self-limiting, resolves in ~6–8 weeks

•    Possible viral trigger

Keratoderma blennorrhagicum

•    Hyperkeratotic plaques on soles/palms

•    Seen in reactive arthritis (Reiter’s syndrome)

Extra Revision Pearls

•    Koebner phenomenon seen in psoriasis, lichen planus, vitiligo

•    Wickham striae characteristic of lichen planus oral lesions

•    Mucosal involvement suggests more severe disease in erythema multiforme (SJS spectrum)

•    Always consider systemic disease (e.g., sarcoid, IBD) in erythema nodosum