Lichen spinulosus (syn. keratosis spinulosa)

Lichen spinulosus is an uncommon condition, usually presenting in childhood, which is characterised by multiple rough, spiny papules that are grouped together in patches or plaques.

This chapter is set out as follows:

• The cause is unknown 

• Lichen spinulosus arises predominantly in childhood, often quite abruptly 

Distribution

• Patches predominantly affect the neck, extensor surfaces of the arms, abdomen, thighs, and knees 

Morphology

• Multiple papules sit within the patches and plaques, which have a diameter of 2-5 cm
• The papules are 1-3 mm in diameter, with a central, rough, horny projection

Differential diagnosis

• Phrynoderma results from a variety of nutritional deficiencies such as Vitamin A, and Vitamin B-complex. It is rare in developed countries. Phrynoderma is characterised by red-brown follicular papules with a central keratotic spinous plug. Lesions tend to be distributed symmetrically and are often localised to the elbows, knees, extensor extremities, and/or buttocks

• ​Multiple minute digitate hyperkeratosis (syn. spiny hyperkeratosis) is a very rare non-follicular digitate keratosis affecting the trunk and limbs. Lesions, which are usually very numerous, are thin, white-yellow, spiny keratotic projections. Occasionally flat-topped, dome-shaped, or crateriform papules are also seen

• Diagnosis is usually clinical. If a diagnostic biopsy is required histology shows dilated hair follicles with a thick keratinous plug, surrounded by a mild to moderate chronic inflammatory infiltrate (reference: Rook's Textbook of Dermatology)

• Most cases resolve spontaneously within 1–2 years, although occasionally lichen spinulosus can be very persistent 

• There is no known effective treatment. A urea-based moisturiser, such as Calmurid ® cream, may help make the skin feel smoother