Hematoxylin-eosin–stained sections showed dilated infundibula with orthokeratotic follicular plugs protruding slightly above the surrounding surface. There was a scant subjacent lymphocytic infiltrate. Fungal and bacterial stains revealed no organisms.
Lichen spinulosus is an idiopathic disorder characterized by scattered 2- to 6-cm patches of keratotic follicular papules. Individual papules are 1 to 3 mm in diameter and consist of a hairlike horny spine.1,2 The clinical appearance results from protrusion of the follicular plugs through the skin surface3 and gives the patch an overall raspy texture. Lesions are typically skin colored and asymptomatic or mildly pruritic.1 They may persist indefinitely if not treated. Other follicular keratotic disorders in the differential diagnosis include keratosis pilaris, lichen planopilaris, pityriasis rubra pilaris, keratosis follicularis (Darier disease), and phrynoderma (hypovitaminosis A).1,4 Histologically, LS is most similar to keratosis pilaris, but differs clinically by its more rapid onset and its tendency to occur in more sharply grouped lesions. Keratosis pilaris is, of course, far more common than LS.
Spiny Eruption on the Neck. Arch Dermatol. 2000;136(9):1165-1170. doi: