Lichen spinulosus is an uncommon dermatosis manifested by large patches of follicular papules topped by keratotic spines, as shown below. In 1883, Crocker published a description of lichen spinulosus. Since then, few other similar reports were published until 1990, when Friedman presented data on 35 patients with lichen spinulosus.  The etiology is unknown. Some minor progress has been made in therapy for lichen spinulosus.
The classic lesion of lichen spinulosus is a keratotic plug located within the dilated follicular orifice. Histologically, an inflammatory lymphohistiocytic infiltrate occurs around the follicle and in the dermis. Hyperkeratosis, parakeratosis, and acanthosis are visible in the follicle. Differentiating lichen spinulosus from keratosis pilaris by microscopy may not be possible.
In the past, lichen spinulosus was reported to be associated with the administration of arsphenamine, thallium, gold, and diphtheria toxin. More recently, authors have noted association with HIV disease  and Crohn disease.  These associations may reflect the interests of the authors. Kabashima et al reported lichen spinulosus in an alcoholic patient. 
Apparently, lichen spinulosus is not a common disorder. This conclusion is based on the paucity of published reports regarding lichen spinulosus.
Lichen spinulosus has been reported worldwide. In 1990, Friedman described 35 patients with lichen spinulosus. He and his coworkers in the Philippines examined 7435 people attending a dermatology clinic.  The incidence of lichen spinulosus was approximately 5 cases per 1000 population with skin disorders. This prevalence exceeds reports from various American surveys on cutaneous diseases in children and adolescents.
Worldwide distribution suggests no predilection of lichen spinulosus in any ethnic group.
Case reports suggest an equal distribution of lichen spinulosus in males and females. Friedman's study in the Philippines included 14 males and 21 females.
Reports indicate that lichen spinulosus is a disease that occurs during childhood to young adulthood. Peak incidence appears to occur during adolescence. Lichen spinulosus can persist for decades. In most patients, lichen spinulosus remits spontaneously within 1-2 years. Friedman calculated that in the Philippines, the average age at onset was 16.2 years ± 10.1 years.
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