Scarring Alopecia Definition
Scarring alopecia (cicatricial alopecia) is a group of disorders characterized by permanent, irreversible hair loss caused by destruction of the hair follicle unit, which is replaced by fibrous scar tissue. 1, 2
Key Defining Features
The fundamental pathologic process involves irreversible damage to epithelial stem cells located in the bulge region of the hair follicle, resulting in permanent follicular destruction. 3
- The hair follicle unit is completely destroyed and replaced by fibrous tissue, making hair regrowth impossible 1, 2
- This represents a trichologic emergency requiring prompt diagnosis and aggressive treatment, as hair loss is irreversible and rapidly progressive 4
Classification Framework
Scarring alopecias are divided into two major categories based on whether the follicle is the primary target:
Primary Cicatricial Alopecia
- The hair follicle itself is the main target of the inflammatory/disease process 1, 2
- Accounts for approximately 5% of all trichologic consultations 2
- Further classified by the predominant inflammatory cell type in the infiltrate 1, 5:
- Lymphocytic: includes discoid lupus erythematosus, lichen planopilaris, frontal fibrosing alopecia, central centrifugal alopecia, and pseudopelade of Brocq 5
- Neutrophilic: includes folliculitis decalvans, tufted folliculitis, and dissecting cellulitis of the scalp 5
- Mixed: includes folliculitis keloidalis 5
Secondary Cicatricial Alopecia
- The follicle acts as an "innocent bystander" in a disease process occurring outside the follicular unit 2
- Hair loss is a secondary consequence of dermal damage rather than primary follicular targeting 2
Critical Diagnostic Distinction
The British Journal of Dermatology emphasizes that determining whether hair loss is scarring or non-scarring through scalp examination fundamentally directs all subsequent diagnostic and therapeutic decisions. 6
- Scarring alopecia shows complete absence of follicular ostia on examination, unlike non-scarring conditions like alopecia areata where follicles remain intact 6
- Scalp inflammation or scaling raises concern for scarring alopecia and requires urgent evaluation 6
Pathogenesis
- The exact mechanisms are not fully understood for most primary cicatricial alopecias 1
- Evidence suggests that collapse of the hair follicle's immunologically "privileged" niche allows inflammatory assault on epithelial stem cells 3
- The common final pathway is follicular destruction regardless of the initiating inflammatory mechanism 2
Clinical Urgency
Early and accurate diagnosis with aggressive treatment is essential to prevent further follicular destruction, as the process is irreversible once scarring occurs. 1, 4
- Patients experience tremendous anxiety, low self-esteem, and extreme psychosocial stress due to permanent, disfiguring hair loss 4
- Treatment aims to halt inflammatory waves and scarring at the earliest phase of involvement 2
- Diagnosis often requires one or more skin biopsies, as clinical features may overlap between different types 1