Lichen Planus Along the Lines of Blaschko

For 2 months, a 72-year-old woman had a rash on her inner right leg that extended from her ankle to her groin. She reported that the rash developed after she had worn a knee brace on the affected leg. Initially, the lesions were slightly red, but they became more purplish over time. She noted that the rash had seemed to improve slightly without any intervention.

The patient had type 2 diabetes, hyperlipidemia, and hypertension; her long-term medications were simvastatin, lisinopril, hydrochlorothiazide, and aspirin. She had no known allergies and denied any alcohol or illicit drug use.

Vital signs were normal. Physical examination revealed numerous violaceous polygonal, planar papules, some with scale and some without, in a linear distribution from the posterior thigh to the medial ankle.

Fluocinonide 0.05% was prescribed, and the patient was instructed to apply it to the affected area twice daily for 1 month. After 1 month of treatment, the appearance of the lesions had significantly improved.

Lichen planus typically manifests as pruritic, purple, planar, polygonal plaques and papules. The lesions of this inflammatory condition can be found on the oral and genital mucosa as well as flexural surfaces of the skin. Because of the appearance and distribution of lichen planus, the differential often includes lichenoid drug eruptions, syphilis, psoriasis, fungal infections, graft-versus-host disease, lichen simplex chronicus, tinea corporis, and herpes zoster.

Lichen planus can be distributed along the lines of Blaschko, which are thought to represent the pathways of epidermal cell migration and proliferation during embryological stages of development. The distribution of the lines of Blaschko does not follow vascular, lymphatic, or neuronal pathways. The lines are V-shaped in the posterior midline (more so on the upper spine), inverted U-shaped on the chest and upper arm, S-shaped on the abdomen, and linear on the legs and lower arms. A literature review by Kabbash and associates¹ found that 11.4% of cases of pediatric lichen planus were linear along the lines of Blaschko; this subvariant is sometimes referred to as Blaschkoian lichen planus. Herpes zoster should be in the differential because variants of lichen planus do not always have Blaschkoian distribution patterns, and even when they do, they can be mistaken as dermatomal.

The diagnosis of lichen planus is made on the basis of the clinical history and examination results. The history may include a change in medications or local trauma prior to the appearance of the lesions. The physical examination focuses on the distribution of the rash and inspection for the characteristic lesions. Punch biopsy is also helpful and will show inflammation and lymphocytic infiltration between the dermis and epidermis in a band-like pattern, leading to hyperkeratosis, as well as epidermal hyperplasia and hypergranulosis in a sawtooth pattern.

The natural course of lichen planus is usually spontaneous resolution within 1 year of onset. About 65% of cases will resolve completely with a 10% to 20% recurrence rate. Treatment is aimed at symptomatic relief of pruritus or improvement in appearance. If a patient is taking a drug that can cause lichen planus, discontinuation of that agent is recommended.²

Treatment can start with twice-daily application of a topical corticosteroid for 2 to 3 weeks. Lesions that are refractory to topical therapy can be treated with intra-lesional triamcinolone injection; oral corticosteroids can also be used. For lesions that do not improve with corticosteroid therapy, acitretin 30 mg/d for 8 weeks is an option as well as PUVA therapy; improvement usually occurs within 8 weeks.

REFERENCES:

1. Kabbash C, Laude TA, Weinberg JM, Silverberg NB. Lichen planus in the lines of Blaschko.
Pediatr Dermatol. 2002;19(6):541-545.

2. Akarsu S, Ilknur T, Ozer E, Fetil E. Lichen planus pigmentosus distributed along the lines of
Blaschko. Int J Dermatol. j.1365-4632. February 23, 2011.

FOR MORE INFORMATION:

•Batra P, Wang N, Kamino H, Possick P. Linear lichen planus. Dermatol Online J. 2008;14(10):16.

•Cho S, Whang KK. Lichen planus pigmentosus presenting in zosteriform pattern. J Dermatol. 1997;24:193-197.

•Hong S, Shin JH, Kang HY. Two cases of lichen planus pigmentosus presenting with a linear pattern. J Korean Med Sci. 2004;19:152-154.

•Rajani K. Lichen planus. Am Fam Phys. 2000;61(11):3319-3324.

•Seo JK, Lee HJ, Lee D, Choi JH, Sung HS. A case of linear lichen planus pigmentosus. Ann Dermatol. 2010;22(3):323-325.

•Yamamoto M, Imai Y, Nakagawa N, Yamanishi K. Lichen planus-like dermatosis distributed along
the lines of Blaschko. J Dermatol. j.1346-8138. September 28, 2010.