Appearance

This presents as a localised demarcated plaque usually with scaling, excoriations and lichenification (increased skin markings and thickened skin) on the surface. The lesion is particularly itchy. Common sites are the calf, elbow, behind neck and genitalia (vulva or scrotum). Plaques are usually greater than 5 cm in diameter.^[1]

The common initial cause is eczema. The intense pruritis leads to persistent scratching and the area becomes lichenified (thick and leathery).

Other common causes include insect bites, scars (eg traumatic, postherpetic/zoster) and venous insufficiency.

Epidemiology^[2]

One study found that the condition occurred in 12% of ageing patients with pruritic skin. The highest prevalence is mid to late adulthood, with a peak at 30-50 years. There is no race predilection, although people with dark skin tend to get more marked pigmentary changes. The condition is aggravated by periods of inactivity (presumably because there are no distractions to the itching) and stress.

Differential diagnosis

A wide range of dermatological conditions need to be excluded, including the dermatological manifestations of systemic diseases of the gastrointestinal, neurological and renal systems, as well as haematological conditions.

Dermatological conditions which need to be considered include:

• Acanthosis nigricans
• Acne keloidalis nuchae - keloid papules and plaques on the occipital scalp occurring almost exclusively in Afro-American men)
• Alopecia mucinosa - papules and plaques seen mainly in the young (<40) leading to hair loss
• Amyloidosis - lichen or macular
• Atopic dermatitis
• Contact dermatitis - allergic or irritant
• Cutaneous T-cell lymphoma
• Dermatitis herpetiformis
• Lichen planus or striatus
• Nummular dermatitis
• Pretibial myxoedema
• Plaque psoriasis
• Seborrheic dermatitis
• Stasis dermatitis
• Tinea cruris

Investigations

Narrowing the list of potential causes may be helped by doing an IgE level and patch testing to exclude atopy and allergy, mycotic studies and biopsy for histopathology.

Primary Care management^[2][3]

• Itching may be relieved by using potent (occasionally very potent) steroids such as clobetasol or fluocinolone. Once the lesion has lost its lichenification and thickening it becomes less itchy and the strong steroids only need to be used if itching recurs.
• Tar or ichthyol preparations have been shown to be beneficial for their anti-pruritic effect.
• Occlusive dressings may help to break the itch-scratch cycle.
• Oral antihistamines may be required. A sedative antihistamine such as chlorphenamine may be first-line if sleep disturbance is a problem.
• Oral antibiotics may be required for swab-positive infections.
• Intralesion steroids such as triamcinolone may be considered in resistant cases.
• Other treatment options currently being investigated include topical doxepin and capsaicin, topical aspirin/dichloromethane, topical and oral immune modulators such as tacrolimus and local botulinus toxin.

Prognosis

The condition often it improves well with treatment but occasional cases may become persistent, especially on the genitalia.

When to refer

For help with diagnosis or treatment.