What is the classification of primary and secondary scarring (cicatricial) alopecia?

Classification of Scarring Alopecia

Scarring (cicatricial) alopecias are classified into primary forms—where the hair follicle is the direct target of destruction—and secondary forms—where follicular destruction occurs as a consequence of a neighboring non-follicular dermatologic process affecting the dermis. 1, 2

Primary Scarring Alopecias

Primary cicatricial alopecias are further subclassified based on the predominant inflammatory cell type in the infiltrate:

Lymphocytic Primary Scarring Alopecias

• Chronic cutaneous (discoid) lupus erythematosus is a lymphocytic scarring alopecia that can cause permanent follicular destruction 1, 3
• Lichen planopilaris represents lymphocytic inflammation targeting hair follicles, with frontal fibrosing alopecia being a variant of this condition 1, 3
• Pseudopelade of Brocq is characterized by lymphocytic inflammation and represents a distinct primary scarring entity 1, 4, 3
• Central centrifugal cicatricial alopecia (previously called diffuse scarring of the vertex in African-Americans) involves lymphocytic inflammation 4, 3

Neutrophilic Primary Scarring Alopecias

• Folliculitis decalvans is characterized by predominantly neutrophilic inflammation and represents one of the most important secondary scarring alopecias in some classification schemes, though it is considered primary in others 1, 4, 3
• Dissecting cellulitis of the scalp (dissecting folliculitis) involves neutrophilic inflammation 1, 3
• Tufted folliculitis is a neutrophilic cicatricial alopecia 3

Mixed Inflammatory Primary Scarring Alopecias

• Folliculitis keloidalis demonstrates a mixed inflammatory infiltrate with both lymphocytes and neutrophils 3

Secondary Scarring Alopecias

In secondary cicatricial alopecias, follicular destruction is not the primary pathologic event but rather occurs as collateral damage from a dermatologic process primarily affecting the reticular dermis or epidermis. 1, 4, 2

Key Distinguishing Feature

• The critical histopathologic distinction is whether the hair follicle itself is the prime target of destruction (primary) versus being involved secondarily in a neighboring non-follicular process that impinges upon and ultimately destroys the follicle (secondary) 2
• Secondary scarring can result from physical trauma, burns, radiation, infections, infiltrative processes, or inflammatory dermatoses where the follicle is not the primary target 2

Diagnostic Approach

Clinical and Dermoscopic Evaluation

• Dermoscopy differentiates non-scarring from scarring alopecia by identifying follicular ostia disappearance in cicatricial forms, while yellow dots and exclamation mark hairs suggest non-scarring alopecia areata 5
• The British Association of Dermatologists emphasizes that early scarring alopecia must be distinguished from alopecia areata, as they are separate entities requiring different management 5

Histopathologic Confirmation

• Skin biopsy is essential when diagnosis is uncertain to definitively distinguish cicatricial from non-scarring alopecia and to subtype primary scarring alopecias 6, 5
• Systematic evaluation using hematoxylin and eosin, Periodic acid-Schiff, and Weigert stains allows accurate diagnosis in over 92% of cases, even in late pauci-inflammatory or non-inflammatory phases 1
• Multiple biopsies may be necessary as these disorders can have similar clinical features despite different etiologies 7

Management Implications

Early and accurate diagnosis with aggressive treatment is critical in primary scarring alopecias to prevent irreversible follicular destruction and permanent hair loss. 7

• The pathogenesis of most primary cicatricial alopecias remains incompletely understood, making histopathologic confirmation particularly important for guiding therapy 7
• Close clinicopathologic correlation is often required for correct diagnosis, as clinical presentation alone may be insufficient 2