What is scarring alopecia?

What is Scarring Alopecia

Scarring (cicatricial) alopecia is a group of disorders characterized by permanent, irreversible hair loss caused by destruction of hair follicle epithelial stem cells in the bulge region, with replacement by fibrous scar tissue—making these conditions trichologic emergencies requiring prompt diagnosis and aggressive treatment. 1, 2

Definition and Pathophysiology

Scarring alopecia represents disorders where the hair follicle unit is destroyed and replaced by fibrous tissue, resulting in permanent hair loss 3. The key pathologic feature is irreversible damage to epithelial stem cells located in the bulge region of the hair follicle, generally through inflammatory mechanisms 2.

Primary vs. Secondary Forms

• Primary cicatricial alopecia occurs when the hair follicle itself is the main target of the autoaggressive immune process, accounting for approximately 5% of all trichologic consultations 3
• Secondary cicatricial alopecia develops when the follicle acts as an "innocent bystander" in diseases occurring outside the follicular unit 3
• Biphasic alopecias are non-scarring conditions that may progress to permanent hair loss in late phases 3

Classification System

Primary cicatricial alopecias are classified according to the predominant inflammatory cell type in the peri-follicular infiltrate 4, 3:

• Lymphocytic forms - characterized by lymphocytic inflammatory infiltrate
• Neutrophilic forms - characterized by neutrophilic inflammatory infiltrate
• Mixed forms - characterized by mixed inflammatory patterns

This classification system was established by the North American Hair Research Society in 2001 3.

Clinical Significance and Urgency

Scarring alopecias are regarded as trichologic emergencies because hair loss is irreversible, rapidly progressive, and can be disfiguring. 1 The urgency stems from several factors:

• Hair follicle destruction is permanent and irreversible once scarring occurs 1, 4
• Disease progression can be rapid without intervention 1
• Patients experience tremendous anxiety, low self-esteem, and extreme psychosocial stress 1
• Some forms may signify underlying systemic disease 5

Diagnostic Approach

Clinical Hallmark Feature

Loss of follicular ostia (hair follicle openings) is the clinical hallmark of scarring alopecia and should be actively searched for during examination 5.

Diagnostic Tools

• Dermatoscopy/trichoscopy can be profitably used for clinical diagnosis and helps distinguish scarring from non-scarring alopecias 5
• Skin biopsy is often necessary—one or more biopsies may be required since these conditions can have similar clinical features 4, 5
• Histopathologic examination is essential for accurate diagnosis, showing follicular destruction and replacement with fibrous tissue 3

Differential Diagnosis Considerations

The British Journal of Dermatology notes that early scarring alopecia can be confused with alopecia areata and may require biopsy for definitive diagnosis 6, 7. This distinction is critical because:

• Alopecia areata is non-scarring with potential for spontaneous remission 6
• Scarring alopecia causes permanent hair loss requiring urgent intervention 1

Management Principles

Early intervention is essential—the aim of treatment is to slow or stop the progression of inflammatory waves and the scarring process at the earliest phase of involvement. 3

• Prompt diagnosis and aggressive treatment are critical since early intervention may slow down or prevent further hair loss 1
• Once scarring has occurred, hair loss is permanent and irreversible 1, 2
• Treatment must be initiated before complete follicular destruction occurs 4

Pathogenesis Insights

The exact mechanisms triggering follicular inflammation in primary cicatricial alopecia remain incompletely understood 4, 2. Current evidence suggests:

• Healthy hair follicle epithelial stem cells normally enjoy relative immunologic "privilege" in their niche 2
• This immunoprotection may collapse in primary cicatricial alopecia, allowing inflammatory assault 2
• The hair follicle becomes the target of autoaggressive immunity, though why this occurs is not fully understood 2