Psoriasis

🔍 When to Suspect

Well-demarcated, erythematous plaques covered with silvery scales, typically on extensor surfaces (elbows, knees), scalp, or lower back

From the full topic in The Ocean Library: Psoriasis

🧭 When to suspect

Psoriasis is a common, chronic, immune-mediated inflammatory skin disease affecting around 2–3% of the UK population, with a characteristic bimodal onset (commonly 15–25 and 50–60 years). The hallmark lesion is a well-demarcated, erythematous plaque with adherent silvery scale, typically on extensor surfaces (elbows, knees), the scalp, sacrum, umbilicus and nails. There is often a family history.

Suspect psoriasis in any recurrent, well-demarcated, scaly eruption, particularly one that is refractory to topical corticosteroids and antifungals. It is frequently misdiagnosed as eczema, tinea, pityriasis rosea or seborrhoeic dermatitis. Classic triggers include streptococcal throat infection (guttate psoriasis), skin trauma (Koebner phenomenon), stress, smoking, alcohol and certain drugs.

The two key primary-care skills are to assess severity and overall impact – psoriasis is a multisystem disorder, so screen for psoriatic arthritis (PsA), cardiovascular and metabolic disease and low mood – and to recognise the dermatological emergencies: erythroderma and generalised pustular psoriasis.

Clinical pattern	Key features
Chronic plaque (psoriasis vulgaris)	The commonest form – well-demarcated erythematous plaques with silvery scale on extensors, scalp, sacrum and umbilicus.
Scalp	Thick adherent scale at the hairline and post-auricular folds; may be the only site involved.
Flexural / inverse	Smooth, glazed, well-demarcated erythema in axillae, groin, natal cleft and submammary folds, with little or no scale; mimics intertrigo or candidiasis.
Guttate	Sudden crop of small "raindrop" plaques over the trunk and limbs in children and young adults, classically 1–2 weeks after a streptococcal throat infection.
Pustular (localised / palmoplantar)	Sterile pustules on palms and soles, strongly associated with smoking.
Generalised pustular psoriasis	Widespread sterile pustules with fever and systemic upset – a dermatological emergency.
Erythrodermic	Confluent erythema affecting > 90% of the body surface area (BSA), with impaired thermoregulation and fluid balance – a dermatological emergency.
Nail	Pitting, onycholysis, subungual hyperkeratosis and "oil-drop" discolouration; an important predictor of psoriatic arthritis.

Source: NICE CG153

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