Dermatology Online Journal

Linear lichen planus
Priya Batra MD, Nadia Wang MD, Hideko Kamino MD, Paul Possick MD
Dermatology Online Journal 14 (10): 16

Department of Dermatology, New York University

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Abstract

A 50-year-old man presented with pruritic, hyperpigmented papules and plaques on the right lower extremity following Blaschko lines. A skin biopsy specimen was consistent with lichen planus (LP). Linear LP accounts for less than 0.2 percent of all patients with LP, and the segmental formation is thought to be due to a postzygotic mutation that affects one of the genes predisposing its development. This loss of heterozygosity may occur from a mutation, deletion, or DNA recombination and leads to the formation of a keratinocyte clone that is more susceptible to development of the skin disease. Histopathologically, linear LP is identical to LP, with the presence of hyperkeratosis, focal hypergranulosis, irregular acanthosis with a sawtooth appearance, vacuolar change of the basal-cell layer, and a dense band-like lymphocytic infiltrate at the dermal-epidermal junction. It is important to differentiate linear LP from lichen striatus, inflammatory linear verrucous epidermal nevus, linear psoriasis, and linear Darier-White disease, which have different presentations clinically and histopathologically.

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Figure 1	Figure 2

History

A 50-year-old man presented to the Charles C. Harris Skin and Cancer Pavilion in October, 2007, with a pruritic, hyperpigmented eruption on his right lower extremity. It started on the right great toe approximately one and one-half years ago and, over the last six months, has spread to involve his right extremity. Lidex ointment was used with minimal improvement. He has no medical problems and takes no medications. Similar lesions are not present in any members of his family. Review of systems is noncontributory.

Physical Examination

Hyperpigmented, well-demarcated, flat-topped papules and small, thin plaques without scale extended from the right great toe around the lateral aspect of the lower leg. Brown-black discoloration of the right great toe nail plate was noted. No oral lesions or genital lesions were present.

Lab

A complete blood count, basic metabolic profile, and hepatic panel were normal. Hepatitis C antibody and hepatitis B surface antigen were negative.

Histopathology

There is a superficial and mid perivascular, perifollicular, and focal band-like infiltrate in the papillary dermis composed of predominantly lymphocytes. At the dermoepidermal junction, there is basal vacuolar change with individually necrotic keratinocytes and pigment incontinence. The epidermis is atrophic with overlying hypergranulosis and orthokeratosis.

Comment

Lichen planus (LP) is an idiopathic inflammatory disease of the skin that affects between 0.2 percent to 1 percent of the adult population. Classic LP is characterized by violaceous, polygonal, pruritic, flat-topped papules with an overlying lace-like scale, which usually occur on the flexor surfaces of the extremities. Mucous membrane involvement is present in up to four percent of the adult population [1]. Pathogenesis is thought to involve T cell-mediated autoimmune damage to the basal keratinocytes in response to agents such as viruses, medications, contact allergens, and even neoplasms [2].

When skin lesions form, they may have a random distribution or follow patterns that were laid down during embryologic development [3]. As a result of cutaneous mosaicism, individuals may have distinct cell populations within their skin that are more likely to develop a skin condition [4]. Linear LP is an example of this phenomenon and accounts for less than 0.2 percent of all patients with LP. Although LP may occur in a linear pattern simply from the Koebner phenomenon, true linear LP is more extensive and follows the lines of Blashko, which are embryogenic developmental pathways [5]. The lines of Blaschko were first described in 1901 and were based on the observed distribution on the skin of various congenital and acquired dermatoses [6].

Because LP is a polygenic skin disease, it may show segmental involvement if a postzygotic mutation affects one of the genes predisposing to its development. This loss of heterozygosity may occur from a mutation, deletion, or DNA recombination and lead to the formation of a keratinocyte clone that is more susceptible to development of the skin disease. This concept was first introduced in 1991 to describe linear psoriasis and, since then, has been applied to segmental forms of atopic dermatitis, erythema multiforme, pemphigus vulgaris, vitiligo, and granuloma annulare in addition to LP [7, 8]. Segmental disease may be superimposed on nonsegmental lesions, with the segmental lesions usually being more difficult to treat. Because of the polygenic nature of LP, family members may have the condition in its nonsegmental form. LP occurs in up to ten percent of first-degree relatives of affected patients.

Histopathologically, linear LP is identical to LP. Lichen planus shows hyperkeratosis, focal hypergranulosis, irregular acanthosis with a sawtooth appearance, vacuolar change of the basal-cell layer, and a dense band-like lymphocytic infiltrate at the dermal-epidermal junction [9]. The dermis may contain rare eosinophils, plasma cells, or macrophages. Civatte bodies, which represent apoptotic keratinocytes, may be present in the lower epidermis or upper dermis [1].

The differential diagnosis of linear LP includes lichen striatus, inflammatory linear verrucous epidermal nevus (ILVEN), linear psoriasis, and linear Darier-White disease. Lichen striatus often affects children, is usually asymptomatic, spontaneously resolves after several months to a year, and is characterized on histopathologic examination by a lichenoid infiltrate that involves the adnexae. Linear psoriasis appears clinically like psoriasis. Inflammatory linear verrucous epidermal nevus is usually present at birth or develops early in childhood. Darier-White disease is easily differentiated by the acantholysis and dyskeratosis seen on histopathologic examination [6].

References

1. Shiohara T, Kano Y. Lichen Planus. In: Bolognia, J et al eds, Dermatology. 2nd edition, London: Mosby, 2008: 159

2. Krasowska D, et al. Unilateral multiple linear lichen planus following the Blaschko lines recurring after deliveries. Dermatology 2001; 202: 340 PubMed

3. Paus R, et al. What is the biological basis of pattern formation of skin lesions? Exp Dermatol 2006; 15: 547 PubMed

4. Frank G, Happle R. Cutaneous mosaicism: right before our eyes. J Clin Invest 2007; 117: 1216 PubMed

5. Sciallis G.F, Loprinzi C.L. Progressive linear lichen planus and metastatic carcinoma. Br J Dermatol 2005; 152: 399 PubMed

6. Kabbash C, et al. Lichen planus in the lines of Blaschko. Pediatr Dermatol 2002; 19: 541 PubMed

7. Grosshans E. Acquired Blaschkolinear dermatoses. Am J Med Genet 1999; 85: 334 PubMed

8. Happle R. Superimposed segmental manifestation of polygenic skin disorders. J Am Acad Dermatol 2007; 57: 690 PubMed

9. Rapini, R. Eczematous and Papulosquamous Diseases. In: Practical Dermatopathology. Philadelphia: Elsevier, 2005: 53

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