Types of Secondary Scarring Alopecia
Secondary scarring alopecia results from nonfollicular scalp conditions that damage the dermis and secondarily destroy hair follicles, as opposed to primary scarring alopecias where the follicle itself is the primary target of inflammation. 1
Classification Framework
Secondary scarring alopecias are histologically distinguished from primary forms by involvement of the reticular dermis rather than primary follicular targeting 2. The key distinction is that the underlying pathologic process affects the dermis first, with follicular destruction occurring as a consequence rather than as the primary event 1.
Major Categories of Secondary Scarring Alopecia
Congenital Defects
- Developmental abnormalities of the scalp can result in areas of permanent alopecia where normal follicular structures never formed or are malformed 1
Traumatic Causes
- Physical injury to the scalp—including burns, mechanical trauma, and radiation injury—causes dermal scarring that secondarily destroys follicles 1
- Traction alopecia in advanced stages can progress to permanent scarring 1
Inflammatory Dermatoses
- Late-stage lupus erythematosus represents one of the most important secondary scarring alopecias, where the inflammatory process extends beyond the follicle to involve the dermis 2
- Sarcoidosis affecting the scalp can cause secondary follicular destruction 1
- Morphea (localized scleroderma) of the scalp produces scarring alopecia through dermal fibrosis 1
Infectious Causes
- Severe bacterial infections (such as carbuncles or abscesses) that extend into the dermis 1
- Deep fungal infections affecting the scalp 1
- Herpes zoster of the scalp in severe cases 1
Neoplastic Causes
- Primary or metastatic tumors involving the scalp destroy follicular structures through tissue replacement 1
- Post-surgical scarring from tumor excision 1
Rare Drug-Related Causes
- Certain medications can rarely cause secondary scarring, though this is an uncommon mechanism 1
Diagnostic Approach
When evaluating suspected secondary scarring alopecia, skin biopsy is essential when diagnosis is uncertain, as end-stage lesions may obscure the underlying disorder 3, 1. Histopathology will show dermal involvement as the primary process with secondary follicular destruction, distinguishing it from primary scarring alopecias 2.
Key Diagnostic Features
- Dermoscopy shows absence of follicular ostia (indicating permanent follicular loss), but lacks the specific features of primary scarring alopecias like yellow dots or exclamation mark hairs 3
- Associated signs and symptoms of the underlying condition (such as systemic lupus features, trauma history, or tumor presence) aid diagnosis 1
- Detection of the underlying disorder may be difficult in end-stage lesions where only fibrosis remains 1
Management Principles
- Treatment is specific for active underlying conditions—addressing the primary dermatologic or systemic disease is essential to prevent progression 1
- Once scarring is established, hair loss is permanent 1
- Surgery and hair transplantation are options for localized scars after the underlying condition is controlled 1
Common Pitfall
The critical error is failing to distinguish secondary from primary scarring alopecia, as this fundamentally changes the treatment approach—secondary forms require treatment of the underlying dermal/systemic condition rather than follicle-directed therapy 2, 1.