Dermatoscopic rainbow pattern in lichen planus pigmentosus inversus in a middle-aged African American man

Introduction

Lichen planus pigmentosus (LPP)-inversus is a rare variant of lichen planus that presents predominately in middle-aged adults as well-demarcated, pruritic, dark-gray plaques in intertriginous zones such as the axilla and inguinal areas.^1,2 To date, only a few cases have been described in the literature. The precise etiology remains unclear; however, several causal agents have been implicated, including hepatitis C and topicals such as mustard oil and perfumes.³

Lichen planus (LP) and its variants are often misdiagnosed in patients with skin of color (SOC),⁴ likely because of limited research on LP in individuals with dark skin. The lack of diversity in images has contributed to dermatologists reporting low confidence when diagnosing skin conditions in SOC.⁵ Moreover, the literature on dermatoscopic findings of LPP in SOC is almost nonexistent.^3,4 Therefore, the objective of this report is to describe an unusual presentation of LP and highlight some of the unique differences and key findings of LPP in SOC.

Case report

A 35-year-old African American man with no significant medical or dermatologic history presented to our academic hospital with a 7-month history of dry patches in the axillae bilaterally. He endorsed mild pruritus in the axillae but denied any pain in the region. The patient had not been evaluated for his condition previously and had not received any treatment for his symptoms. When asked about potential triggers or exacerbating factors, the patient denied a recent history of trauma, infection, drug use, or use of new oils, perfumes, or antiperspirants.

A dermatologic examination revealed multiple hyperpigmented dark-brown-to-purple annular lesions, some in a linear array, with satellite 1- to 2-mm, shiny, violaceous papules on the posterior aspect of the axillae (Fig 1, A). Confluent flat-topped, scaly, dark-gray papules and plaques, some with fine white scales, were also visible in the axillae (Fig 1, B). No abnormalities were observed on the palms, soles, mucous membranes, or nails.

Fig 1.

A, Multiple hyperpigmented dark lesions, some in a linear array, with satellite millimetric, shiny, violaceous papules. B, Confluent flat-topped, scaly, violaceous papules and plaques, some with fine white scales visible in the axilla.

Dermatoscopy was used to aid in the diagnosis. We observed annular dark, purple-colored lesions with peripheral tramming, with scaling surrounding violaceous plaques (Fig 2, A and B). There were dark, violaceous, macular lesions with an annular granular pattern. Atop some lesions were whitish-blue, reticular fine lines, whereas others appeared with gray-blue globules with white dots in the background (Fig 2, C and D). Additionally, in many of the lesions, we observed a rainbow pattern (Fig 2, B).

Fig 2.

A,B, Dermatoscopic images showing annular, purple-colored lesions with peripheral tramming and scaling (red arrow). There was an annular granular pattern at the periphery of the lesions, likely due to pigment incontinence secondary to previously healed lesions (black arrow). Some lesions showed a rainbow pattern (purple arrow). C, Violaceous plaques with whitish, reticular, fine lines on the surface (orange arrow). D, Round Wickham striae surrounding a dark spot, known as the black-hole pattern (yellow arrow), and gray-blue globules over the pigmented lesions. Notably, none of the lesions showed vascular features.

The differential diagnosis of this patient’s presentation included LP, sarcoidosis, and granuloma annulare. A punch biopsy of the annular lesion shown in Fig 2, B was performed. Histology revealed a superficial band-like, lymphocytic, inflammatory infiltrate that extended to the epidermis (Fig 3, A). There was also lichenoid inflammation, with wedge-like hypergranulosis, mild hyperkeratosis, basal vacuolization, and individual necrotic epidermal keratinocytes and melanophages (Fig 3, B). The histiocytes were positive for S100 stain (Fig 3, D). This confirmed the diagnosis of LPP. The appearance of lesions in the intertriginous areas rather than in sun-exposed areas, as in classic LPP, made LPP-inversus the most likely diagnosis.² Consent for the publication of all patient photographs and medical information was provided by the authors at the time of article submission to the journal stating that the patient gave consent for his photographs and medical information to be published in print and online and with the understanding that this information may be publicly available.

Fig 3.

Histologic images of lesions. A, Basket-weave stratum corneum with epidermal acanthosis, with wedge-shaped, lymphocytic, inflammatory infiltrate in the superficial dermis with conspicuous pigment incontinence (hematoxylin-eosin stain; original magnification: ×4.) B, Higher magnification showed mild hyperkeratosis with epidermal acanthosis, hypergranulosis, and saw-tooth appearance of the dermoepidermal junction, with an underlying lichenoid infiltrate and interface changes as well as individual necrotic epidermal keratinocytes and melanophages (hematoxylin-eosin stain; original magnification: ×10.) C, Large histiocytes with abundant pale cytoplasm and emperipolesis of lymphocytes and plasma cells (hematoxylin-eosin stain; original magnification: ×20.) D, The histiocytes were positive for S100 stain (S100 stain; original magnification: ×20.)

Discussion

LPP predominantly occurs in persons with darker skin and presents as hyperpigmented papules and plaques that appear dark brown or gray.^1,6 In darker skin, the lesions of LPP can appear dark brown or gray rather than pink or violaceous, as is the case in lighter skin types.⁶

Although dermatoscopy has been shown to be beneficial in diagnosing LPP,⁴ there are limited descriptive studies or images available in the literature involving dermatoscopic findings of LPP in SOC. Vázquez-López et al⁷ conducted a previous study in which 3 dermatoscopic patterns of LPP were defined: diffuse, dotted, and mixed. The diffuse pattern is characterized by brown, structureless areas, whereas the dotted pattern is characterized by a coarse, gray-blue or brown globus. In our patient, we observed brown, structureless areas with a conspicuous rainbow pattern and peripheral tramming, likely due to heavy pigmentation in skin type VI and the heavy pigment incontinence seen using histology. The rainbow pattern has been previously reported as the main pattern seen in Kaposi sarcoma.⁸ It has also been reported in LP and lichen sclerosus et atrophicus but not yet in LPP.^4,9,10 The rainbow pattern may result from polarized light interacting with structural components in these lesions. The rich vascular network, diffuse homogeneous fibrosis, and dense lymphocytic infiltrate of lichenoid dermatosis may contribute to this phenomenon; however, the exact mechanism is not well established.^8,9

In addition, we observed Wickham striae in small, patchy lesions, which appear bluish gray using dermatoscopy, on our patients’ darker skin. This is consistent with Wickham striae on SOC, which often appear globular as well as veil like and bluish rather than pearly white on light skin.^3,4 There were several white rings surrounding dark spots, a finding known as the black-hole pigmentation pattern (Fig 2, D). García-García et al⁴ studied LP in 5 patients with skin types V and VI and proposed that the black-hole pattern may be more common in dark skin. Additionally, the dotted, dark-brown pattern suggests hyperpigmentation, which is a characteristic of LPP and a feature that is more common in patients with darker skin.⁷ Lastly, we noted the lack of vascular features, which may be less viable on darker skin types.⁴

Conclusion

Here, we present the physical, dermatoscopic, and histologic findings of a patient with SOC presenting with a rare diagnosis of LPP-inversus. Further research is warranted to elucidate both predisposing factors for LPP-inversus and unique presentations in patients with SOC. Future research should also seek to clarify the progression of LPP-inversus and incorporate images of underrepresented skin types to improve the lack of diversity in images present in the current literature. Finally, we hope that this case can serve as a learning tool for dermatologists to familiarize clinicians with this rare diagnosis and its presentation in SOC.

Conflicts of interest

None disclosed.