Why does the diagnosis of lichen planus pigmentosus (LPP), characterized by a hem-like pattern in the face and intertriginous areas, particularly in individuals with darker skin types, require the expertise of a dermatologist skilled in dermoscopy?

Dermoscopic Features of Lichen Planus Pigmentosus in Face and Intertriginous Areas

Lichen planus pigmentosus (LPP) in facial and intertriginous areas displays a characteristic "hem-like" pattern on dermoscopy due to deep dermal pigmentary incontinence, which creates diffuse brownish hues with irregularly distributed dots and globules—features that require dermoscopic expertise to distinguish from clinically similar conditions like acanthosis nigricans, post-inflammatory hyperpigmentation, and erythema dyschromicum perstans. 1

Why Dermoscopy Expertise is Essential

Diagnostic Challenge in Darker Skin Types

• LPP predominantly affects individuals with darker skin phototypes, where clinical examination alone cannot reliably differentiate between multiple hyperpigmentation disorders that present similarly in flexural areas 1, 2
• The intertriginous variant (lichen planus pigmentosus inversus/LPPI) can closely mimic acanthosis nigricans clinically, presenting as symmetric hyperpigmented dark brown patches in axillary and other flexural regions 1

Specific Dermoscopic Patterns Requiring Expert Recognition

• The "hem-like" pattern manifests as a diffuse brownish background hue with dots and globules of inconsistent size and distribution, reflecting dermal melanophage deposition from pigmentary incontinence 1
• Expert dermoscopists can identify the absence of hyperkeratosis and papillomatosis that would suggest acanthosis nigricans, and the reduction in density and color intensity of pigmented structures that characterizes LPP 1, 3
• The dermoscopic accuracy depends critically on the clinician's experience and familiarity with the technique, as emphasized for pigmented lesion evaluation 4, 5

Differential Diagnosis Requiring Dermoscopic Expertise

Conditions That Mimic LPP in These Areas

• Acanthosis nigricans: Would show velvety texture with papillomatosis on dermoscopy, absent in LPP 1
• Post-inflammatory hyperpigmentation from contact dermatitis: Lacks the specific dot-globule pattern and diffuse brownish hue characteristic of dermal pigmentary incontinence 1
• Symmetrical drug-related intertriginous and flexural exanthema (SDRIFE): History and acute presentation differ, but dermoscopy helps confirm chronicity 1
• Fixed drug eruption: More circumscribed lesions with different dermoscopic architecture 1
• Erythema dyschromicum perstans: Requires dermoscopic differentiation based on pigment distribution patterns 1

Clinical Context Supporting Dermoscopic Findings

Distribution Patterns

• LPP-inversus specifically affects flexural and intertriginous areas (axillae, groin, inframammary folds) while sparing sun-exposed areas, unlike classic LPP which favors face and neck 2
• Friction is an associated trigger in intertriginous LPP, explaining the predilection for these sites 2
• The face remains a common site for classic LPP, particularly in sun-exposed areas 2

Histopathologic Correlation

• Dermoscopic findings must correlate with histopathology showing absence of hyperkeratosis and papillomatosis (ruling out acanthosis nigricans), presence of basal hydropic degeneration with lymphohistiocytic infiltrates, and numerous melanophages in the dermis 1, 6
• The deep dermal pigmentary incontinence visible on dermoscopy as the hem-like pattern corresponds to melanophage deposition seen histologically 1, 3

Practical Approach for Diagnosis

Three-Pronged Evaluation

1. Thorough history: Document triggers (sun exposure, contactants like mustard oil or nickel, friction), associated conditions (hepatitis C, autoimmune diseases, endocrinopathies), and medication use 2

2. Dermoscopic examination by experienced operator: Look specifically for diffuse brownish hue with dots and globules of inconsistent size, lightening of background color in treated cases, and absence of papillomatosis features 1, 3

3. Histopathological confirmation: Mandatory before treatment initiation, showing characteristic features without hyperkeratosis/papillomatosis 1

Common Pitfall to Avoid

• Do not rely on clinical appearance alone in facial and intertriginous LPP, as multiple conditions present with similar hyperpigmentation in these areas—dermoscopy bridges the gap between clinical suspicion and histopathologic confirmation 1
• The harmonious overlap between patient-reported improvement, physician-graded improvement, and dermoscopic changes validates dermoscopy as an objective monitoring tool for treatment response 3

Treatment Monitoring Value

• Dermoscopy provides objective assessment of treatment efficacy by documenting lightening of background color and reduction in density/color intensity of pigmented structures over time 3
• This is particularly valuable given that LPP is notoriously treatment-refractory due to deep dermal pigmentary incontinence 3, 2