Asymptomatic Discolored Lesions on the Groin

The Diagnosis: Lichen Planus Pigmentosus-Inversus

Histopathologic examination revealed hyperkeratosis with dense, bandlike, lymphocytic inflammation at the dermoepidermal junction with associated melanin-containing macrophages in the papillary dermis (Figure 1). The physical examination and histopathology were consistent with a diagnosis of lichen planus pigmentosus-inversus (LPPI). Treatment was discussed with the patient, with options including phototherapy, tacrolimus, or a high-dose steroid. Given that the lesions were asymptomatic and not bothersome, the patient denied treatment and agreed to routine follow-up.

Figure 1. Lichen planus pigmentosus-inversus. A, Hyperkeratosis with lymphocytic inflammation at the dermoepidermal junction with melanin-containing macrophages in the papillary dermis (H&E, original magnification ×40). B, Bandlike lymphocytic infiltrate at the dermoepidermal junction (H&E, original magnification ×20).

The first case of LPPI was reported in 20011; since then, approximately 100 cases have been reported in the literature.² A rare variant of lichen planus, LPPI predominantly occurs in middle-aged women.^2,3 Lichen planus pigmentosus-inversus is characterized by well-circumscribed, brown macules confined to non-sun-exposed intertriginous areas such as the axillae and groin.² Although the rash remains localized, multiple lesions could arise in the same area, such as the groin as seen in our patient (Figure 2). Unlike in lichen planus, the oral mucosa, nails, and scalp are not affected. Furthermore, pruritus typically is absent in most cases of LPPI.^2,4 Histopathologic findings include an atrophic epidermis with lichenoid infiltrates of lymphocytes and histocytes as well as substantial pigmentary incontinence with melanin-containing macrophages in the papillary dermis.^4,5

Figure 2. Lichen planus pigmentosus-inversus. Well-circumscribed, hyperpigmented macules on the lower abdomen and groin.

Given the gender, age, and clinical features of our patient, this case represents a classic scenario of LPPI. It currently is unknown if ethnicity plays a role in the disorder. Lichen planus pigmentosus-inversus initially was thought to be more prevalent in White patients; however, studies have been reported in individuals with darker skin.^1,2

The main differential diagnosis includes erythema dyschromicum perstans, postinflammatory hyperpigmentation, and lichen planus. Although erythema dyschromicum perstans develops in individuals with darker skin, lesions are restricted to the upper torso and limbs.^2-4 In both lichen planus and lichen actinicus, skin findings primarily develop in sun-exposed areas, such as the face, neck, and hands.^4,6 Given the negative history of trauma, postinflammatory hyperpigmentation was unlikely in our patient. Furthermore, a distinguishing characteristic of LPPI is the deposition of melanin deep within the dermal layer.³

Lesions developing in nonexposed intertriginous skin makes LPPI unique and distinguishes it from other more common conditions. The lesions commonly are hyperpigmented and are not as pruritic as other lichen-associated conditions. Lichen planus pigmentosus-inversus often persists for months, and the rash generally is resistant to treatment.^2,5 Topical tacrolimus and high-dose steroids may improve symptoms, though results have varied substantially. In addition, some cases have resolved spontaneously.^1,4,6,7 Because LPPI is asymptomatic and benign, spontaneous resolution and routine care is a reasonable treatment strategy. Some cases have supported this strategy as safe and high-value care.²