Pruritus, localised skin

Probability diagnosis

Atopic dermatitis (eczema)

Contact dermatitis (irritant and allergic)

Urticaria

Insect bites/infestations

Psoriasis

Simple pruritus (cause not found)

Other disorders

Infection/infestations:

• scabies

• pediculosis (scalp, body, pubic)

• tinea cruris

• Candida intertrigo

• bed bugs

Non-infection:

• pityriasis rosea

• lichen planus

• dermatitis herpetiformis

• asteatosis (dry skin)

• prickly heat (miliaria/heat rash)

• Grover disease

• chilblains

• seborrhoeic dermatitis (usually mild)

Consider (rare):

• myeloproliferative disorders

• cutaneous T-cell lymphoma

Masquerades checklist

Depression

Diabetes

Drugs

Is the patient trying to tell me something?

Psychogenic including dermatitis artefacta.

Key history

Includes past history, especially chronic dermatoses (particularly atopic dermatitis and contact dermatitis), diabetes and psychological disorders. Enquire about exposure to infestations such as ‘backpacker’ lodgings, scabies and sexual contact. Drug history is important.

Key examination

• General and localised examination of the skin

• Note any scratch marks

• Look for evidence of insects such as scabies, lice and bed bugs, the violaceous rash of lichen planus and the vesicles of dermatitis herpetiformis

Key investigations

• FBE/ESR

• Blood sugar

• Microscopic examination of skin scrapings

• Skin biopsy

Diagnostic tips

• Pruritus is a feature of dry skin, common in the elderly.

• An intense localised itch is suggestive of scabies or bed bugs.