Pityriasis lichenoides

Pityriasis lichenoides is a less common condition occurring in acute and chronic forms.

The acute form presents with widespread pink papules which itch and form crusts, sometimes with vesicle formation suggestive of chickenpox. There may be ulceration. The lesions may develop in crops and resolve over a matter of weeks.

The chronic form presents as reddish brown papules—often with a "mica"-like scale that reveals a smooth, red surface underneath, unlike the bleeding points of psoriasis. In lichen planus there is no superficial scale and blistering is unusual.

The distribution is over the trunk, thighs, and arms, usually sparing the face and scalp.

The underlying pathology—vascular dilatation and a lymphocytic infiltrate with a keratotic scale—is in keeping with the clinical appearance. The cause is unknown.

Treatment is with topical steroids. Ultraviolet light treatment is also helpful.

Characteristics of pityriasis lichenoides

Clinical features of psoriasis

Clinical features of eczema

Possible family history

Possible family history

Sometimes related to stress

Sometimes worse with stress

Itching—rare

Usually itching

Extensor surfaces and trunk

Flexor surfaces and face

Well defined, raised lesions

Poorly demarcated lesions

Hyperkeratosis

Oedema, vesicles, lichenification

Scaling, bleeding points

Secondary infection sometimes

beneath scales

present

Koebner's phenomenon

Nails affected

Scalp affected

Mucous membranes

not affected

Pityriasis lichenoides showing acute erythematous rash

Pityriasis lichenoides—distribution pattern

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