Lichen Nitidus

Lichen nitidus is a chronic, usually asymptomatic eruption of tiny, uniform, shiny, flesh coloured papules, found most often on the genitals, abdomen, chest and flexor forearms. It affects children and young adults.

It is rare, with equal sex incidence, and is somewhat more visible in darker skin. It typically lasts months to a few years and resolves spontaneously in most patients.

Variants include generalised, actinic, palmoplantar, vesicular, haemorrhagic and linear forms. It sometimes coexists with lichen planus. The cause is unknown, and an isomorphic response at sites of skin injury is common.

Pathophysiology.

A focal granulomatous like lymphohistiocytic infiltrate sits in the upper dermis beneath a thinned epidermis. The epidermis at the margins of the infiltrate extends downward around it, giving a characteristic claw-clutching-a-ball appearance on biopsy. The cause of the immune reaction is not known.

• Discrete, dome shaped, shiny papules of 1 to 2 mm, flesh coloured or slightly red brown, in groups, and occasionally in linear streaks at sites of injury.
• Distribution on the penis, abdomen, chest, forearms and inner thighs. Mucosal and nail involvement are uncommon, with nail pitting in some cases.
• Usually asymptomatic, with mild itch in a minority.
• Palmoplantar variant: hyperkeratotic fissured plaques of the palms and soles.

• Clinical diagnosis from the characteristic papules.
• Dermoscopy shows well defined, round, shiny papules with a pale centre.
• Skin biopsy for atypical or generalised disease: a nodular infiltrate with epithelioid cells, lymphocytes and giant cells enclosed by epidermal rete ridges.
• Exclude infection and sarcoidosis, with tests selected by the clinical picture.

Differential diagnosis. Lichen planus, lichen spinulosus, keratosis pilaris, flat warts, molluscum contagiosum, papular eczema, milia, lichenoid sarcoidosis and papular tuberculide.

• Reassure the patient that the condition is benign and usually resolves without treatment, with no scarring.
• Moderate potency topical corticosteroid (clobetasone butyrate 0.05%) or potent corticosteroid (betamethasone valerate 0.1%) once daily for 2 to 4 weeks for itchy or extensive lesions. Avoid very potent preparations on the genitals.
• Tacrolimus 0.1% ointment twice daily, or 0.03% for children and for the face and genitals, as a steroid sparing option.
• Generalised or symptomatic disease: narrowband ultraviolet B two to three times weekly. Acitretin 25 to 50 mg daily is used rarely for resistant disease (teratogenic, with strict contraception).
• The evidence for all treatments is weak.

Monitoring. Review at 3 to 6 months. Re-evaluate if lesions change or if other lichenoid disease appears.

Referral and escalation. Refer to dermatology if the diagnosis is uncertain, or the disease is generalised, symptomatic or persistent.

Special groups. In children avoid potent steroids on the genitals and face, and prefer tacrolimus 0.03% for steroid sparing treatment.