Tinea Capitis

How It Develops: Patterns of Hair Shaft Invasion

Depending on where the fungal spores form and how they are arranged relative to the hair shaft, tinea capitis falls into three main invasion patterns:

• Ectothrix Invasion: spores form a sheath around the outside of the hair shaft (the cuticle), while hyphae grow inside it. The main culprits are Microsporum canis (caught from cats and dogs) and Microsporum gypseum (from soil). Spores building up on the outer surface damage the cuticle, so the hair loses its shine, weakens and snaps a few millimeters above the scalp.
• Endothrix Invasion: spores grow inside and completely fill the core of the hair shaft (the cortex), while the outer cuticle stays intact. Typical causes are Trichophyton tonsurans and Trichophyton violaceum (spread from person to person). With the core packed with spores, the hair becomes very brittle and breaks right at the follicle opening, leaving small black dots on the scalp.
• Favus: caused by Trichophyton schoenleinii. Hyphae and spores grow inside the hair shaft along with air bubbles. This produces characteristic yellow, cup-shaped crusts (scutula) around the follicle openings, leading to scalp atrophy and permanent hair loss.
• Kerion Celsi Inflammatory Reaction: kerion is not caused by bacteria. It results from an intense delayed-type (type IV) hypersensitivity response by the host to antigens from zoophilic fungi (M. canis, T. verrucosum). Neutrophils pour in and form micro-abscesses around the follicles, destroying the hair stem cells in the bulge region.

Clinical Features and Differential Diagnosis

Clinical Types:

• Gray patch tinea capitis: usually ectothrix (M. canis). One or more well-defined round patches of hair loss, 1–5 cm across, covered in fine gray dandruff-like scale. All the hairs in the patch are broken off 2–4 mm above the scalp and look dull and gray. Itching is usually mild.
• Black dot tinea capitis: usually endothrix (T. tonsurans). Many small, scattered patches of hair loss with poorly defined edges. Because the hairs break right at the scalp surface, the stumps left in the follicle openings appear as dense, tiny black dots. Scale may be mild or almost absent.
• Kerion celsi: a deep, raised, boggy pustular nodule with clear borders, its surface riddled with honeycomb-like openings that ooze thick yellow pus. Light pressure squeezes pus out of the follicle openings. Hair in the area falls out completely or pulls out easily and painlessly. Patients often have a low-grade fever and tender swollen lymph nodes behind the ears or in the neck.
• Favus: thick, bright yellow, cup-shaped crusts (scutula) form around the hair roots, with a depressed center and a characteristic "mousy" odor. Lifting a crust leaves a red, raw, bleeding base. Over time the crusts shed, leaving red, atrophic scalp and permanent scarring baldness.

Differential Diagnosis in the Clinic:

• Seborrheic dermatitis: thick, sticky, yellow greasy scale on the crown and along the hairline, but no broken hairs or short-stubble hair loss.
• Scalp psoriasis: very well-defined red plaques with thick, silvery-white scale that often extends beyond the hairline. Hairs keep growing through the scale normally without breaking.
• Alopecia areata: completely smooth bald patches with no scale or inflammation. "Exclamation mark hairs" may be seen at the advancing edge, but there are no broken gray hairs or black dots.

Our Diagnostic Workup at Haute-Derma

• Wood's Lamp Examination: 365 nm UV light is shone directly on the scalp in a fully darkened room. Infection with Microsporum species (ectothrix) glows a bright green from pteridine produced by the fungus. Trichophyton schoenleinii (favus) gives a pale blue-green glow. Trichophyton tonsurans (endothrix) does not fluoresce at all (negative).
• Trichoscopy (Scalp Dermoscopy): reveals microscopic features typical of each type. Ectothrix: boomerang-shaped hairs and band-like scale around the hair openings. Endothrix: comma hairs, corkscrew hairs, Morse code-like hairs and black dots. Kerion: red, eroded skin, pustules around the follicles and enlarged vessels.
• KOH Microscopy with Fluorescent Staining: scalp scale is scraped and broken hairs are plucked and soaked in 10–20% KOH. Under a Calcofluor White fluorescence microscope, we can see exactly where the spores sit: in chains inside the hair shaft (endothrix) or coating its outer surface (ectothrix).
• Fungal Culture to Identify the Species: affected hairs are cultured on Sabouraud dextrose agar (SDA) with chloramphenicol and cycloheximide. Colony appearance is followed for 2–3 weeks to pinpoint M. canis, T. tonsurans or T. verrucosum.

Comprehensive Treatment at Haute-Derma

Important clinical note: tinea capitis cannot be cured with creams or shampoos alone, because the fungus lives deep inside the hair shaft and follicle. Oral antifungal treatment is essential.

• First-Line Oral Antifungal Therapy:
  • Griseofulvin (first choice for Microsporum): pediatric dose 15–20 mg/kg/day (microsize), once daily or in two divided doses. It must be taken with a fatty meal (whole milk, yogurt, butter) to maximize absorption. Duration: 6–8 weeks.
  • Terbinafine (first choice for Trichophyton): children under 20 kg, 62.5 mg/day; 20–40 kg, 125 mg/day; over 40 kg and adults, 250 mg/day. Duration: 4–6 weeks.
  • Itraconazole: 5 mg/kg/day continuously for 4 weeks, or pulse therapy for older children and adults.
• Topical Support and Clearing Hidden Carriers: wash with 2% ketoconazole or 2.5% selenium sulfide shampoo 2–3 times a week, leaving it on for 10 minutes before rinsing, to kill loose spores on the scalp and reduce spread to others. We advise all family members to use 2% ketoconazole shampoo for 2 weeks to clear asymptomatic carriage.
• Urgent Management of Kerion Celsi: never incise and drain a kerion: it is a hypersensitivity reaction, not a simple bacterial abscess, and cutting it is painful and increases the risk of scarring. Oral corticosteroids (prednisolone 0.5–1 mg/kg/day) are added for the first 1–2 weeks under cover of systemic antifungals to calm the destructive inflammation quickly and protect the hair stem cells in the bulge region.