What is the proper procedure for performing a skin scrape on a pediatric patient suspected of having tinea capitis?

How to Perform a Skin Scrape for Tinea Capitis

For tinea capitis, use a blunt scalpel to scrape the affected scalp areas, collecting scale and broken hair stubs, and combine this with hair plucking of affected hairs for optimal diagnostic yield. 1, 2

Specimen Collection Technique

Primary Method: Scalp Scraping

• Use a blunt scalpel to scrape the scalp surface, focusing on areas with visible scale, broken hairs, or inflammation 1, 2
• Scrape vigorously enough to collect both scale and hair stubs, particularly targeting "black dot" areas where hairs have broken off at the scalp surface 2
• The scalpel technique is preferred because it collects both fungal elements from the scalp surface and broken hair fragments containing arthroconidia 3

Complementary Sampling Methods

Multiple sampling techniques should be performed during the same visit to maximize diagnostic yield: 2, 4

• Hair plucking: Use forceps to pluck 10-15 affected hairs (not cut them), selecting hairs that appear broken, dull, or are in areas showing fluorescence under Wood's lamp if M. canis is suspected 2
• Brush sampling: Massage a sterile toothbrush or cytobrush over the affected scalp areas for 10-15 seconds, which collects spores and scale 1, 2
• Gauze swab: Rub a moistened gauze pad over affected areas as an alternative collection method 2, 4

Pre-Collection Steps

Wood's Lamp Examination

• Perform Wood's lamp examination before specimen collection if Microsporum species are suspected (based on local epidemiology or animal contact history) 2
• M. canis infections show bright green fluorescence, allowing you to target specifically affected hairs for plucking 2
• Note that Trichophyton species (including T. tonsurans, the most common cause in North America) do not fluoresce, so a negative Wood's lamp does not rule out tinea capitis 5, 6

Dermoscopy (If Available)

• Use dermoscopy to identify characteristic features before sampling: comma-shaped hairs, corkscrew hairs, black dots, and broken hair stubs 2, 7
• This helps target the most productive areas for specimen collection 2

Specimen Handling

Critical Storage Requirements

• Place specimens in paper envelopes or card packs, never in plastic containers 2
• Plastic traps moisture and promotes bacterial overgrowth that can obscure fungal elements 2
• Label clearly with patient information and clinical suspicion 1

Laboratory Processing

• Request both microscopy (KOH preparation) and fungal culture on Sabouraud agar with cycloheximide 1, 2, 4
• KOH microscopy (10-30% solution) provides rapid preliminary diagnosis within hours 4
• Culture requires at least 2 weeks of incubation and identifies the specific dermatophyte species, which guides treatment selection 1, 4

Common Pitfalls to Avoid

• Don't rely on a single sampling method: Using only one technique reduces diagnostic sensitivity; combining scalp scraping with hair plucking increases yield 2, 4
• Don't collect insufficient material: Inadequate specimen collection is a major cause of false-negative results 1
• Don't use plastic containers: This is a critical error that can ruin specimens 2
• Don't wait for mycology results if clinical suspicion is high: In the presence of kerion, significant scale, lymphadenopathy, or alopecia, it is reasonable to start treatment while awaiting confirmatory results 1

Post-Treatment Sampling

• Repeat mycological sampling is mandatory after completing the standard treatment course to document mycological clearance 2, 4
• Continue monthly sampling until clearance is confirmed, as clinical improvement alone is insufficient to determine cure 2, 4
• Treatment should not be stopped based solely on clinical appearance without mycological confirmation 2, 4