What Is the Cause of the Patch on This Man’s Chin?

A 46-year-old South Asian man with skin type IV presented with a linear brown-gray patch extending from his chin onto his anterior neck (Figure 1). The lesion had been present for 7 months with no associated symptoms and remained stable in appearance over this period. He denied previous trauma to the area, new exposures, or previous dermatologic history. A shave biopsy performed at an outside dermatology office showed acanthosis. The patient was given fluocinonide ointment, which he used for 2 weeks with no significant change.

What Is The Diagnosis?

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Linear Lichen Planus Pigmentosus

Lichen planus pigmentosus (LPP) is a rare pigmentary disorder and subtype of lichen planus that is most prevalent among skin type III-IV individuals.¹ It presents as dark brown to gray macules and patches in photoexposed areas, although involvement of intertriginous regions and along the lines of Blaschko have been reported.

LPP along the lines of Blaschko may be categorized as a linear, segmental, or zosteriform distribution.² Linear LPP commonly presents on the face and neck as reported in this case.² Linear LPP has been commonly reported in Asian men between their first and sixth decades of life, which was the demographic group of our patient.¹ This is contrary to the preponderance in women who are menopausal that is typically reported for nonlinear LPP.¹

Although the cause of LPP is unknown, it is suspected to be immune mediated. LPP is likely caused by T-cell dysregulation, in which CD8+ T-cells target and destroy epidermal keratinocytes, leading to pigment incontinence and dermal pigmentation.¹ In linear LPP, dyspigmentation along the lines of Blaschko may exemplify genetic mosaicism, in which the lines correlate with migration of T-cells and clonal expression during the embryonic phase.^1-3

On histopathology, LPP is characterized by vacuolar degeneration of the basal cell layer of the epidermis, a patchy band-like lichenoid infiltrate, perivascular lymphocytes within the papillary dermis, and dermal melanophages reflecting pigment incontinence.^1,2 Epidermal atrophy and hyperkeratosis may also be visualized.¹

LPP may present in conjunction with other systemic diseases, including hepatitis C, type 2 diabetes mellitus, and autoimmune diseases.¹ It may also be associated with increased sun exposure; various topical agents, such as nickel and henna; and topical and oral consumption of mustard oil.^1,2 Additionally, products that include musk ambrette; sandalwood, bergamot, rosemary, or lavender oil; or lime can trigger LPP.⁴

The differential for patients with this presentation includes linear lichen planus, linear morphea, lichen striatus, erythema dyschromicum perstans, and postinflammatory hyperpigmentation.

LPP is chronic in nature and clinical improvement is often gradual.¹ Treatment options include topical medications, such as corticosteroids, tacrolimus, hydroquinone, retinoids, and other lightening agents. Oral treatments, including dapsone and isotretinoin, have shown promise in some patients. Laser therapy with the Q-switched Nd:YAG laser has also been successful in reports.^1,2 Combination treatments with either topical compounds or a combinationof topical, oral, and/or procedural treatments can be considered.Patients may also choose not to receive treatment.

Sun protection is advised, regardless of the patient’s method of treatment, to prevent exacerbation of the pigmentation or recurrence after clinical improvement. Patients should also avoid identified triggers, such as nickel, hair dye, and alma oil.¹ The duration of therapy and need for maintenance therapy are currently unknown.¹ Associated disorders should be treated in conjunction with LPP to prevent further progression.

Physical examination revealed a dark brown to gray atrophic linear patch extending from the chin to the anterior neck. The differential included linear LPP, linear morphea, linear lichen planus, lichen striatus, pigmentary mosaicism, and postinflammatory hyperpigmentation.A punch biopsy was performed for further evaluation revealing mild epidermal atrophy with significant hyperkeratosis and hypergranulosis. The basal cell layer had a sparse, superficial band-like lymphohistiocytic infiltrate with focal squamatization. Occasional necrotic keratinocytes and focal, deep periadnexal inflammation were noted (Figure 2). Melanin-laden macrophages were also prevalent throughout the papillary dermis. Our patient’s clinical and histologic findings were consistent with previously reported cases of linear LPP,^2,3 and a diagnosis of linear LPP was confirmed.

The patient was started on a topical compound containing hydroquinone, kojic acid, niacinamide, corticosteroid, and tretinoin and was encouraged to apply sunscreen daily. He has not yet returned to the clinic for follow up.

In summary, linear LPP is a difficult to treat, acquired pigmentary disorder with unclear etiology and pathogenesis that should be included in the differential for patients presenting with hyperpigmented linear patches, particularly on the head and neck.

1. Robles-Méndez JC, Rizo-Frías P, Herz-Ruelas ME, Pandya AG. Lichen planus pigmentosus and its variants: review and update. Int J Dermatol. 2018;57(5):505-514. doi:10.1111/ijd.13806

2. Arpa MG, Flores-Terry MÁ, González-Ruiz L, Villasanti-Rivas N. Linear facial lichen planus pigmentosus. An Bras Dermatol. 2019;94(3):378-379. doi:10.1590/abd1806-4841.20198537

3. Seo JK, Lee HJ, Lee D, Choi JH, Sung HS. A case of linear lichen planus pigmentosus. Ann Dermatol. 2010;22(3):323. doi:10.5021/ad.2010.22.3.323

4. Mendiratta V, Sanke S, Chander R. Lichen planus pigmentosus: a clinico-etiological study. Indian Dermatol Online J. 2019;10(3):288. doi:10.4103/idoj.IDOJ_253_18