What are the indications for a scalp biopsy in patients with scalp symptoms or suspected scalp conditions?

Scalp Biopsy Indications

Scalp biopsy should be performed when the diagnosis of a scalp condition remains uncertain after clinical examination and dermoscopy, particularly for suspected cicatricial (scarring) alopecia, diffuse alopecia areata that is diagnostically challenging, early or atypical presentations of hair loss, and when differentiating between chronic telogen effluvium and female pattern hair loss in women with mild to moderate (stage 1-2) hair loss. 1

Primary Indications for Scalp Biopsy

Uncertain or Atypical Presentations

• Biopsy is indicated when clinical diagnosis remains uncertain despite dermoscopy, particularly in early or atypical presentations of hair loss where characteristic features are absent 1
• Diffuse alopecia areata that is diagnostically challenging requires histopathologic confirmation, especially when presenting without characteristic dermoscopic findings like yellow dots and exclamation mark hairs 1
• When the differential diagnosis includes conditions requiring different management approaches (e.g., distinguishing scarring from non-scarring alopecia), biopsy provides definitive diagnosis 1

Cicatricial (Scarring) Alopecia

• Suspected cicatricial alopecia is a primary indication for scalp biopsy, as early diagnosis and treatment are critical to prevent irreversible hair loss 1, 2
• Dermoscopy-guided biopsy should be used to select the optimal site based on specific features: perifollicular concentric white scales in lichen planopilaris and frontal fibrosing alopecia, hair tufts in folliculitis decalvans, or follicular red dots/keratotic plugs in discoid lupus erythematosus 2
• This technique yields a definitive pathological diagnosis in 95% of cases by precisely identifying even individually affected follicles in early or focal disease 2

Chronic Diffuse Hair Loss in Women

• Scalp biopsy should be reserved for women with mild to moderate (mid-scalp clinical grade 1 or 2) chronic diffuse hair loss to distinguish between chronic telogen effluvium and female pattern hair loss 3
• Women with severe hair loss (clinical grade 3,4, or 5) do not require biopsy, as 97% have female pattern hair loss on histopathology 3
• Triple horizontal biopsies achieve 98% diagnostic accuracy versus 79% with single biopsy, though single biopsy remains acceptable in clinical practice 3

Systemic Disease Evaluation

• Biopsy is indicated when systemic conditions like lupus erythematosus or secondary syphilis are in the differential diagnosis and require histopathologic confirmation 1
• Serology for lupus or syphilis should accompany biopsy when these conditions are suspected 1

Optimal Biopsy Technique

Dermoscopy-Guided Approach

• Always perform dermoscopy before biopsy to identify the most active disease site, looking for yellow dots, exclamation mark hairs, perifollicular scales, or other characteristic features 1, 2
• Dermoscopy-guided biopsy is fast, precise, and allows morphologic characterization of particular follicular structures, especially valuable in early or focal cicatricial alopecia 2

Technical Considerations

• Two 4-mm punch biopsies should be obtained from the vertex or mid-scalp: one for horizontal sectioning and one for vertical sectioning 3
• Horizontal sectioning at the mid-isthmus level allows assessment of the terminal to vellus-like hair ratio (T:V ratio), which is diagnostic for female pattern hair loss (T:V <4:1) versus chronic telogen effluvium (T:V >8:1) 3
• The biopsy specimen size and depth must be adequate to provide accurate diagnosis and identify aggressive growth patterns if present 4

When Biopsy Is NOT Indicated

Clinically Evident Diagnoses

• Laboratory investigations and biopsy are unnecessary in most cases of alopecia areata when the diagnosis is clinically evident with characteristic patchy hair loss and dermoscopic features 1
• Tinea capitis should be diagnosed by fungal culture (scalp scraping, hair pluck, brush, or swab) rather than biopsy 4
• Women with severe (stage 3-5) female pattern hair loss do not require biopsy confirmation 3

Alternative Diagnostic Methods Sufficient

• When dermoscopy reveals pathognomonic features (yellow dots and exclamation mark hairs in alopecia areata), clinical diagnosis without biopsy is appropriate 1
• Fungal culture is mandatory before treating suspected tinea capitis, as it is the most common cause of treatment failure when diagnosis is made on clinical grounds alone 4

Critical Pitfalls to Avoid

• Do not order excessive laboratory tests or perform biopsy when the diagnosis is clinically evident, as this wastes resources and delays treatment 1
• Do not biopsy without first performing dermoscopy, as this may result in sampling from an inactive or non-representative site, yielding non-diagnostic results 2
• Do not rely on a single biopsy technique—both horizontal and vertical sectioning provide complementary information, particularly for chronic diffuse hair loss 3
• Repeat biopsy should be considered if the initial specimen is inadequate for accurate diagnosis 4
• Do not delay fungal culture in suspected tinea capitis—biopsy is not the appropriate diagnostic test for fungal infections 4