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). There is often a family history.

The hallmark lesion is a well-demarcated, erythematous plaque with adherent silvery scale, typically on:

• Extensor surfaces (elbows, knees)

• The scalp, sacrum and umbilicus

• The nails

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

• Seborrhoeic dermatitis

Classic triggers include:

• Streptococcal throat infection (guttate psoriasis)

• Skin trauma (Koebner phenomenon)

• Stress

• Smoking

• Alcohol

• Certain drugs

The two key primary-care skills are:

• Assess severity and overall impact – psoriasis is a multisystem disorder, so screen for psoriatic arthritis (PsA), cardiovascular and metabolic disease and low mood.

• 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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