Lichen Spinulosus

Lichen spinulosus is a rare follicular disorder in which grouped keratotic spines project from clusters of follicles and form well defined patches. It is most common on the neck, trunk, buttocks, limbs and extensor surfaces.

It occurs in children and young adults, more often in boys, and usually resolves spontaneously within months to a few years, though recurrence is possible. It is regarded as a follicular reaction rather than a distinct disease.

It has been linked to atopic dermatitis, hypothyroidism, HIV infection, Crohn disease, vitamin A deficiency, other nutritional deficiency and drugs such as phenytoin, and sometimes follows a viral illness or a drug reaction. In many patients no cause is found.

Pathophysiology.

Follicular hyperkeratosis forms a keratin plug that extends from the follicular opening as a filiform spine, with a mild perifollicular lymphocytic infiltrate. The exact mechanism is unclear, and vitamin A deficiency and drug reaction are thought to act through altered follicular keratinisation.

• Groups of 1 to 2 mm follicular papules, each with a central filiform keratotic spine, in sharply demarcated patches of 2 to 5 cm that feel like a nutmeg grater.
• Distribution on the neck, back, abdomen, buttocks and extensor limbs, with sparing of palms and soles.
• Often asymptomatic, with mild itch in a minority.
• Resolution without scarring.

• Clinical diagnosis from the morphology, with exclusion of underlying causes where suggested by the history.
• Skin biopsy only when the diagnosis is uncertain: dilated follicles with keratin plugs and a perifollicular lymphocytic infiltrate.
• Consider thyroid function, serum retinol, HIV test and bowel assessment when the history indicates.
• Review of drug history.

Differential diagnosis. Keratosis pilaris, lichen nitidus, pityriasis rubra pilaris, phrynoderma (vitamin A deficiency), follicular eczema, lichen planopilaris, trichostasis spinulosa and papular secondary syphilis.

• Emollients and keratolytics: urea 10 to 20% or salicylic acid 2 to 5% preparations once or twice daily.
• Topical retinoid: tretinoin 0.025 to 0.05% cream, or adapalene 0.1% gel, at night as tolerated. Avoid in pregnancy.
• Mild to moderate topical corticosteroid (hydrocortisone 1% or clobetasone butyrate 0.05%) once daily for 2 to 4 weeks when itchy or inflamed.
• Treat any underlying cause, such as thyroid disease or vitamin A deficiency, and stop an implicated drug if possible.
• Acitretin 10 to 25 mg daily is used only for extensive resistant disease (teratogenic, with strict contraception).
• Evidence for all measures is weak, and spontaneous resolution is usual.

Monitoring. Review at 8 to 12 weeks.

Referral and escalation. Refer to dermatology if the diagnosis is unclear or the disease is extensive or persistent.

Special groups. Topical retinoids and acitretin are contraindicated in pregnancy. Use mild preparations in young children.