A 42-year-old Indian woman with Fitzpatrick IV skin presents with a 2-year history of insidious, asymptomatic slate-gray to dark brown macules and patches on the forehead, temples, and lateral neck. The lesions are ill-defined, non-scaly, and lack the classic Wickham striae. Dermoscopy reveals diffuse brownish-gray dots, globules, and short linear structures. The structure marked **C** in the diagram is suspected based on these clinical and dermoscopic findings. Which of the following histopathological findings is MOST characteristic of this condition and distinguishes it from other pigmentary disorders in skin of color?

Question

Accepted Answer

C. Vacuolar degeneration of the basal layer with pigment incontinence and dermal melanophages. ## Why vacuolar degeneration of the basal layer with pigment incontinence and dermal melanophages is right

The structure marked **C** — lichen planus pigmentosus (LPP) — is definitively characterized by vacuolar degeneration of the basal layer with prominent pigment incontinence and numerous dermal melanophages on histopathology. This interface dermatitis pattern with melanin spillage into the dermis is the hallmark that distinguishes LPP from other pigmentary disorders affecting Indian skin. The sparse lymphocytic lichenoid infiltrate and apoptotic keratinocytes further support this diagnosis (IADVL Textbook of Dermatology 5e; Kanwar AJ Indian J Dermatol 2014).

## Why each distractor is wrong

- **Epidermal hyperplasia with increased melanin in basal keratinocytes and minimal dermal involvement**: This pattern is characteristic of melasma (marked **A**), which shows epidermal melanosis without significant dermal involvement or pigment incontinence. Melasma also presents with bilateral symmetric brown patches on the cheeks, forehead, and upper lip — not the flexural and lateral neck distribution seen in LPP.

- **Perivascular lymphocytic infiltrate with preserved basal layer integrity and superficial dermal melanosis**: This pattern is more consistent with erythema dyschromicum perstans/ashy dermatosis (marked **B**), which may show early erythematous raised rims and lacks the prominent vacuolar basal degeneration characteristic of LPP. While there is overlap between LPP and ashy dermatosis, the preserved basal layer integrity is not typical of LPP.

- **Reticulate pattern of melanin deposition in the epidermis with intact dermal-epidermal junction**: This describes Riehl melanosis (marked **D**), a pigmented contact dermatitis with reticulate brownish pigmentation and a history of cosmetic allergen exposure (hair dyes, fragrances). The dermal-epidermal junction remains relatively intact, unlike the vacuolar degeneration seen in LPP.

**High-Yield:** LPP is defined by pigment incontinence with dermal melanophages — melanin escapes the basal layer into the dermis, creating the slate-gray color on clinical exam and the characteristic dermoscopic dots and globules.

[cite: IADVL Textbook of Dermatology 5e; Kanwar AJ Indian J Dermatol 2014]

Answer

A. Epidermal hyperplasia with increased melanin in basal keratinocytes and minimal dermal involvement

Answer

B. Reticulate pattern of melanin deposition in the epidermis with intact dermal-epidermal junction

Answer

D. Perivascular lymphocytic infiltrate with preserved basal layer integrity and superficial dermal melanosis

Explanation

Why vacuolar degeneration of the basal layer with pigment incontinence and dermal melanophages is right

Why each distractor is wrong

Practice similar questions