Violaceous Flat-Topped Papules and Plaques


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A 39-year-old African American man presents to the clinic with a 5-month history of a pruritic rash on his back. His wife noticed that he has had several purple-colored bumps on his back that appear to be growing and spreading. The patient is otherwise healthy but reports a remote history of intravenous drug use. On examination, there are multiple violaceous flat-topped papules and plaques located on the patient’s back. He does not have any other lesions on his body.

Lichen planus (LP) is an inflammatory condition of unknown cause that primarily affects mucocutaneous surfaces. It most commonly involves the skin of the extremities (cutaneous LP) and oral mucosa (oral LP), but it is known to affect the hair, nails,...

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Lichen planus (LP) is an inflammatory condition of unknown cause that primarily affects mucocutaneous surfaces. It most commonly involves the skin of the extremities (cutaneous LP) and oral mucosa (oral LP), but it is known to affect the hair, nails, and other mucous membranes including the esophagus and genitalia.1-3 LP is estimated to affect <1% of the population and tends to present in middle age, typically between 30 and 60 years.1-3 Cutaneous LP does not have a predilection for race or sex, but oral LP appears to affect women more often than men.4 The condition rarely occurs in children, with pediatric LP accounting for only 1% to 4% of cases.5

The pathogenesis of LP is not well understood.1-7 Activated CD4+ and CD8+ T lymphocytes have been implicated in an immune-mediated mechanism whereby they are recruited to the dermal-epidermal junction and interact with basal keratinocytes. Upregulations in intercellular adhesion molecule-1 and T-helper-1 cytokines such as interferon-γ, tumor necrosis factor-α (TNF-α), and nuclear factor-kb-dependent cytokines lead to basal keratinocyte apoptosis.3 Other proposed mechanisms include upregulation of matrix metalloproteases and mast cell-mediated release of chemokines that disrupt the epithelial basement membrane.6

LP is known to be associated with hepatitis C virus infection (HCV), which may play an important role in the pathogenesis of the disease. A meta-analysis of 70 studies showed that the prevalence of HCV exposure was significantly greater among patients with LP compared with control patients (odds ratio, 5.4).7 In addition, patients with HCV infection have a higher prevalence of LP than the general population.7 Therefore, clinicians should have a low threshold for suspecting LP in patients with HCV who present with clinical features suggestive of the disease. Other risk factors that have been identified in association with LP include genetic polymorphisms in interferon-γ promoter and TNF-α genes.6 Exposure to certain drugs such as β-blockers, nonsteroidal anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, and penicillamine can cause lichenoid drug eruptions, which resemble idiopathic LP.1,3

The clinical characteristics of LP are manifold and vary based on the site of involvement. Cutaneous LP presents with a widespread, papulosquamous eruption of erythematous to violaceous isolated, flat-topped papules and plaques that commonly involve the extremities, especially the flexor surfaces of the ankles and wrists. These findings are commonly referred to as the “6 Ps”: purple, pruritic, polygonal, planar, papules, and plaques. Koebner phenomenon due to scratching of lesions is often observed. Variants of cutaneous LP include hypertrophic LP, which is characterized by thick plaques, and bullous LP, which results in vesicles and or bullae within the lesions.1-3

Oral LP can occur either alone or in conjunction with other forms of LP. Oral LP most frequently involves the posterior buccal mucosa, gingiva, and tongue and can be classified into 3 types: reticular, erythematous, and erosive.1,2,4 Lesions of reticular oral LP are often asymptomatic and characterized by a lacelike network of white lines known as Wickham striae on the mucosa. Erythematous LP appears as atrophic, erythematous patches. Erosive LP can result in painful, burning ulcers or rarely bullae.1-4

Nail involvement is not uncommon and occurs in 1% to 16% of patients; fingernails are more frequently affected than toenails.2 LP of the nails results in nail thinning, longitudinal ridging, and distal splitting, which leads to onycholysis and subungual hyperkeratosis.1,3 These changes have been shown to involve the nail matrix. When the nail plate splits longitudinally, the central area is raised and the lateral edges are angled downward, resulting in an “angel wing deformity.”2

Histologic findings include thickening of the stratum corneum with focal orthokeratosis, liquefactive degeneration of the basal cell layer, irregular acanthosis, and an eosinophilic amorphous band at the basement membrane. Wickham striae appear to be due to a thickened granular cell layer. The characteristic histologic feature is a band-like inflammatory infiltrate composed of lymphocytes and histiocytes adjacent to the basal layer.1,2,4

Diagnosis of LP is based on clinical findings.1,3 A thorough physical examination should focus on all sites of potential involvement including the skin, mucosa, genital area, nails, and hair. No specific laboratory-based test exists, but screening for HCV infection is recommended.1,3,7 A careful drug history may elicit a cause for a lichenoid drug eruption.1,3 Skin biopsy and histopathology can confirm the diagnosis by demonstrating the lymphohistiocytic infiltrate at the dermal-epidermal junction with associated degeneration of basal keratinocytes.3

Differential diagnosis includes other papulosquamous disorders such as psoriasis, pityriasis rosea, lichen nitidus, lichen striatus, and lichenoid drug eruptions, but a careful history and clinical findings can usually differentiate between these.1,2 Genital involvement in LP resulting in desquamative vaginitis, for example, can be mistaken for lichen sclerosis or atrophic vaginitis. Oral LP may be mimicked by secondary syphilis, candidiasis, leukoplakia, or discoid lupus erythematosus. Histologically, LP is extremely difficult to differentiate from discoid lupus erythematosus, with no consensus as to the exact microscopic features to distinguish between the 2 disorders; the differentiating factors are clinical.2

LP is usually benign and self-limited, resolving within a few years.1-3 First-line treatment is high-potency topical corticosteroids, although their efficacy has not been evaluated with clinical studies.1-3,5 Intralesional corticosteroid injections can also be used in larger or hypertrophic lesions.3 Second-line therapy consists of systemic corticosteroids such as oral prednisone or intramuscular injections of triamcinolone; data are inconclusive regarding shorter (weeks) vs longer-course (months) treatments. Oral retinoid therapy has also been reported to successfully treat LP, but the side effects and longer length of therapy should be deliberated before beginning treatment. Phototherapy, including combined psoralen and long-wave ultraviolet A radiation (PUVA) and narrow-band UVB, can also be utilized in conjunction with other treatment modalities, but clinical trial data are still limited. Case studies also support treatments such as antihistamines, griseofulvin, dapsone, cyclosporine, and other immunomodulators.1-3,5

The patient in the case described applied 0.05% betamethasone dipropionate cream to the lesions twice daily for 1 month and dramatic regression of his cutaneous lesions was noted by 1-month follow-up.

Kelvin Wang, BSE, is a medical student; Talia Noorily, BA, is a medical student; and Christopher Rizk, MD, is a dermatology fellow at Baylor College of Medicine, Houston, Texas.


  1. Le Cleach L, Chosidow O. Clinical practice. Lichen planus. N Engl J Med. 2012;366(8):723-732.
  2. Boyd AS, Neldner KH. Lichen planus. J Am Acad Dermatol. 1991;25(4):593-619.
  3. Lehman JS, Tollefson MM, Gibson LE. Lichen planus. Int J Dermatol. 2009;48(7):682-694.
  4. Eisen D. The clinical features, malignant potential, and systemic associations of oral lichen planus: a study of 723 patients. J Am Acad Dermatol. 2002;46(2):207-214.
  5. Pandhi D, Singal A, Bhattacharya SN. Lichen planus in childhood: a series of 316 patients. Pediatr Dermatol. 2014;31(1):59-67.
  6. Roopashree MR, Gondhalekar RV, Shashikanth MC, George J, Thippeswamy SH, Shukla A. Pathogenesis of oral lichen planus—a review. J Oral Pathol Med. 2010;39(10):729-734.
  7. Shengyuan L, Songpo Y, Wen W, Wenjing T, Haitao Z, Binyou W. Hepatitis C virus and lichen planus: a reciprocal association determined by a meta-analysis. 2009;145(9):1040-1047.
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