A 42-year-old woman of South Asian descent presents with a 2-year history of progressive, asymptomatic hyperpigmented lesions on her forehead, temples, and lateral neck. On examination, she has multiple ill-defined, slate-gray macules as marked **A** in the diagram, predominantly on sun-exposed areas. Dermoscopy reveals pigment incontinence with dermal melanophages. Which of the following best explains the pathophysiological mechanism responsible for the slate-gray coloration seen in the lesion marked **A**?

Question

Accepted Answer

B. Melanin spillage from damaged basal keratinocytes into the dermis, taken up by dermal melanophages, producing color via the Tyndall effect. ## Why option 2 is right

Lichen planus pigmentosus (LPP) is a CD8+ T-cell-mediated cytotoxic disorder that disrupts the dermoepidermal junction, causing basal keratinocytes to undergo apoptosis (Civatte bodies). This disruption allows melanin to spill into the dermis, where dermal melanophages (macrophages) phagocytose the melanin. The characteristic slate-gray to brown color results from the Tyndall effect — the optical scattering of light by melanin particles in the deeper dermis, which absorbs longer wavelengths and reflects shorter (blue) wavelengths, creating the slate-gray appearance. This pigment incontinence is the hallmark histopathological finding in LPP and directly explains the clinical presentation in lesion **A** (Bolognia Dermatology 5e; Indian Journal of Dermatology 2020).

## Why each distractor is wrong

- **Option 1**: This describes normal melanin physiology and epidermal pigmentation seen in melasma or post-inflammatory hyperpigmentation, not the pathological pigment incontinence characteristic of LPP. Lesion **A** shows dermal, not epidermal, melanin deposition.
- **Option 3**: LPP is characterized by an atrophic epidermis, not thickened epidermis. Melanin trapped in the stratum granulosum would produce a brown or tan color, not the deep slate-gray hue seen in lesion **A**.
- **Option 4**: Hemosiderin deposition produces a yellow-brown or rust-colored appearance typical of stasis dermatitis or post-inflammatory changes, not the slate-gray coloration of LPP. Vascular ectasia is not a feature of LPP pathogenesis.

**High-Yield:** Pigment incontinence + Tyndall effect = slate-gray color in LPP; this distinguishes it from melasma (epidermal, lighter) and erythema dyschromicum perstans (ashy, trunk-predominant).

[cite: Bolognia Dermatology 5e; Indian Journal of Dermatology 2020]

Answer

A. Vascular ectasia in the superficial dermis with hemosiderin deposition

Answer

C. Melanin synthesis in the basal keratinocytes with upward migration to the stratum corneum

Answer

D. Increased epidermal thickness with melanin trapped in the stratum granulosum

Explanation

Why option 2 is right

Why each distractor is wrong

Practice similar questions