What is the pathophysiology, signs, symptoms, diagnosis, management, and differential diagnosis of scarring alopecia?

Scarring Alopecia: Comprehensive Clinical Overview

Pathophysiology

Scarring alopecia results from irreversible destruction of epithelial stem cells in the hair follicle bulge region, leading to permanent replacement of follicles with fibrous scar tissue. 1

The pathogenic mechanisms include:

• Collapse of immune privilege: Healthy hair follicle stem cells normally exist in an immunologically privileged niche that protects them from inflammatory assault; this protection breaks down in primary cicatricial alopecia (PCA), though the exact triggers remain incompletely understood 1

• Inflammatory targeting: In primary scarring alopecias, the hair follicle itself is the primary target of autoaggressive immunity, whereas in secondary forms, the follicle acts as an "innocent bystander" to disease processes occurring outside the follicular unit 2, 3

• Classification by infiltrate: PCAs are categorized by the predominant inflammatory cell type—lymphocytic, neutrophilic, or mixed—which reflects distinct immunologic pathways driving follicular destruction 2, 3

Signs and Symptoms

Look for patches of permanent hair loss with visible scalp scarring, absence of follicular openings, and associated symptoms of active inflammation. 3

Key clinical features to identify:

• Visible scarring: Smooth, shiny scalp surface with complete absence of follicular ostia in affected areas 3, 4

• Active inflammation indicators: Perifollicular erythema, scaling, pustules, or crusting suggest ongoing disease activity requiring aggressive intervention 2

• Pattern recognition: Distribution patterns vary by subtype—frontal hairline involvement suggests frontal fibrosing alopecia, vertex involvement suggests lichen planopilaris, and crown involvement suggests central centrifugal cicatricial alopecia 5

• Associated symptoms: Pruritus, burning, pain, or tenderness often accompany active inflammatory phases 3

Diagnostics

Scalp biopsy is mandatory for definitive diagnosis, as clinical features alone are often insufficient to distinguish between scarring alopecia subtypes. 2, 3

Diagnostic Algorithm:

Step 1: Clinical Assessment

• Examine for follicular dropout, scarring, and inflammation patterns 3
• Document distribution and extent of hair loss photographically 6

Step 2: Dermoscopy/Trichoscopy

• Perform trichoscopy to identify loss of follicular openings, perifollicular scaling, and inflammatory features that guide biopsy site selection 6
• Trichoscopy helps differentiate scarring from non-scarring alopecias and monitors treatment response 6

Step 3: Histopathologic Confirmation

• Obtain 4mm punch biopsies from areas showing active inflammation at the periphery of hair loss, not from completely scarred central areas 3, 4
• Request both horizontal and vertical sectioning for optimal follicular assessment 4
• Histology reveals follicular destruction with fibrous tract replacement and characterizes the inflammatory infiltrate (lymphocytic vs. neutrophilic vs. mixed) 2, 4

Step 4: Laboratory Testing

• Check for underlying systemic disease when indicated: ANA and anti-dsDNA for discoid lupus erythematosus, bacterial culture for folliculitis decalvans 3
• Fungal culture if tinea capitis cannot be excluded clinically 7

Common Pitfall: Delaying biopsy while attempting empiric treatment allows irreversible follicular destruction to progress 2, 3

Management

Initiate aggressive anti-inflammatory therapy immediately upon diagnosis to halt progression, as any delay results in permanent, irreversible hair loss. 2, 3

Treatment Algorithm by Disease Activity:

Active Inflammatory Phase (Priority: Stop Progression)

• First-line: Intralesional corticosteroids (triamcinolone acetonide 5-10 mg/mL) injected monthly into active borders 3

• Concurrent systemic therapy for extensive disease:

  • Oral corticosteroids (prednisone 0.5-1 mg/kg/day) for rapid control, then taper 3
  • Add steroid-sparing immunosuppressants: hydroxychloroquine 200-400 mg daily, mycophenolate mofetil 1-2 g daily, or methotrexate 15-25 mg weekly 3

• Refractory cases: Consider off-label biologics or JAK inhibitors, with TNF-α inhibitors, IL-17 inhibitors, and JAK inhibitors showing the most promise for disease stabilization 5

Stabilized/Inactive Phase

• Continue maintenance immunosuppression at lowest effective dose to prevent recurrence 3
• Monitor every 3-6 months with clinical examination and trichoscopy for early detection of reactivation 6, 3

Subtype-Specific Considerations:

• Folliculitis decalvans: Add prolonged oral antibiotics (rifampin plus clindamycin) targeting Staphylococcus aureus 3
• Discoid lupus erythematosus: Hydroxychloroquine is particularly effective 3
• Frontal fibrosing alopecia: 5α-reductase inhibitors (finasteride 5 mg daily) may slow progression 3

Critical Caveat: No treatment reverses established scarring; all interventions aim solely to halt further destruction 2, 3

Patient Counseling

Inform patients immediately that scarring alopecia causes permanent hair loss that cannot be reversed, making early aggressive treatment essential to preserve remaining hair. 2, 3

Key Counseling Points:

• Permanence of hair loss: Destroyed follicles are replaced by scar tissue and will never regrow hair, even with treatment 3, 1

• Treatment goals: All therapies aim to stop disease progression and preserve existing hair, not to restore lost hair 2, 3

• Urgency of treatment: Delays in diagnosis or treatment allow irreversible follicular destruction to continue unchecked 2

• Psychological impact: Permanent hair loss profoundly affects quality of life; assess for anxiety and depression and offer psychological support resources 7

• Long-term monitoring: Lifelong surveillance is necessary as disease can reactivate even after years of quiescence 3

• Cosmetic options: Once disease is stabilized, discuss camouflage techniques, wigs, or hair transplantation into stable scarred areas (though transplants carry risk of disease reactivation) 3

Differential Diagnosis

Distinguish scarring from non-scarring alopecias first, then differentiate between scarring alopecia subtypes using clinical patterns, dermoscopy, and histopathology. 7, 6

Primary Scarring Alopecias (Follicle is Primary Target):

Lymphocytic:

• Lichen planopilaris: Perifollicular erythema and scaling, often at vertex 3
• Frontal fibrosing alopecia: Symmetric frontal hairline recession with eyebrow loss 5, 3
• Central centrifugal cicatricial alopecia: Crown involvement, predominantly affects women of African descent 5, 3
• Discoid lupus erythematosus: Associated with systemic lupus, requires ANA testing 7, 3

Neutrophilic:

• Folliculitis decalvans: Pustules, crusting, positive bacterial culture 5, 3
• Dissecting cellulitis: Painful nodules and draining sinuses on scalp 5, 3

Mixed:

• Erosive pustular dermatosis: Elderly patients with scalp trauma history 3

Non-Scarring Alopecias to Exclude:

• Alopecia areata: Exclamation mark hairs, yellow dots on dermoscopy, preserved follicular openings, potential for complete regrowth 7, 6
• Trichotillomania: Incomplete hair loss, broken hairs firmly anchored, no follicular destruction 7, 6
• Tinea capitis: Requires fungal culture, responds to antifungals 7, 6
• Telogen effluvium: Diffuse shedding, preserved follicles, reversible 7

Secondary Scarring Alopecias (Follicle is Bystander):

• Physical trauma: Burns, radiation, traction 3
• Infections: Bacterial (kerion), fungal (severe tinea), viral (herpes zoster) 3
• Neoplasms: Metastases, primary skin tumors 3

Diagnostic Pitfall: "Biphasic alopecias" like long-standing traction alopecia or androgenetic alopecia can eventually develop secondary scarring in late stages, blurring the distinction between scarring and non-scarring forms 3