An 8-year-old Hispanic boy presents for evaluation of mildly itchy, pinpoint bumps that have been present for 2 to 3 months. The “rash” is primarily involving the patient’s trunk. Patient is otherwise healthy, and no one else at home has a similar eruption. The mother of the patient has tried some over-the-counter hydrocortisone, which has helped some with the mild itching, but the lesions persist. The pediatrician noted the linear pattern of the pinpoint papules and made the clinical diagnosis of lichen nitidus (Figure 139-1). These lines represent the Koebner phenomenon caused by scratching done by the child in areas that are reachable.
FIGURE 139-1
Lichen nitidus with several linearly arranged groups of tiny, skin-colored papules amidst a background of scattered pinpoint papules on the trunk of a child. The linearly arranged groups of papules are secondary to scratching (Koebner phenomenon). (Used with permission from John Browning, MD.)
Lichen nitidus and lichen striatus are two distinct entities under the umbrella of lichenoid dermatoses, a grouping that is based on clinical findings resembling lichen planus, the prototypical lichenoid dermatosis, and the characteristic histologic findings of a band-like inflammatory infiltrate with or without vacuolar alteration of the dermoepidermal junction. Both conditions can present in a linear array; lichen nitidus because it exhibits the Koebner phenomenon (Figure 139-1) and lichen striatus (Figure 139-2) because it follows the lines of Blaschko. We will further discuss some of the similarities and distinguishing features of these two entities.
Lichen nitidus is a relatively rare disorder, more common in children and young adults.
Lichen nitidus often presents in preschool and school-aged children.
There does not seem to be a race or sex predilection.
Lichen striatus is seen primarily in children 5 to 15 years of age.1
Females are more often affected than males, with some reports of a female to male ratio as great as 2-3:1 (Figure 139-3).
Lichen nitidus was once thought to be a tuberculous reaction because of its distinctive histologic findings of a lymphohistiocytic infiltrate, but no infectious agents have ever been elucidated.
Lichen striatus is also thought to be related to infectious agents, viruses in particular. This postulation is based on the predominance of lichen striatus in children and its tendency to appear more commonly in the spring and summer.
The Blaschkoid distribution of lesions in lichen striatus point to a somatic mutation as another potential cause, but no gene association has been established.
Some hypothesize that a combination of the two previously mentioned processes may be required for development of lichen striatus.
Still, lichen striatus may be related to atopy.
There are no proven risk factors, but some authors do believe that lichen nitidus is a cutaneous manifestation of Crohn’s disease.2
Atopy may be a predisposing factor for lichen striatus, but it is suspected that an infectious agent is still a necessary trigger.
Lichen nitidus is characterized by numerous, discrete, skin-colored, shiny, flat-topped 1 to 2mm papules, clustered in groups (Figures 139-4 and 139-5). If inflammatory, the papules may appear more red.
FIGURE 139-5
Close-up view of lichen nitidus with scattered skin-colored, flat-topped papules on the trunk. (Used with permission from Richard P. Usatine, MD.)
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