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Keratinous Inflammatory Lesion (Kerion) – Deep Fungal Scalp Infection

Overview

Kerion is a severe, inflamed form of tinea capitis (scalp ringworm) that presents as a boggy, pus‑filled mass on the scalp. It results from a deep, hypersensitivity reaction to dermatophyte fungi—most commonly Trichophyton tonsurans, T. violaceum, or Microsporum canis. The condition is also called “kerion celsi” or “inflammatory tinea capitis”.

• Typical age group: Children 3–12 years old, because the immature immune response of young children predisposes to a vigorous inflammatory reaction.
• Gender: Slight male predominance (≈1.2 : 1) reported in several epidemiologic studies.
• Geographic prevalence: More common in warm, humid climates and in low‑to‑middle‑income countries. In the United States, the CDC estimates an overall tinea capitis prevalence of 2–5 % in school‑age children, with kerion representing 10–15 % of those cases.
• Public health impact: Outbreaks occur in schools, daycare centers, and boarding schools, making early recognition essential to prevent transmission.

Symptoms

Kerion develops over days to weeks and is distinguished from a non‑inflamed tinea capitis by the following signs:

Local scalp findings

• Large, tender, boggy swelling (2 cm–10 cm) with a raised, firm edge.
• Pustules and crusts that may coalesce, giving a “cobblestone” appearance.
• Hair loss (alopecia) localized to the lesion; hairs may be broken off at the scalp surface (called “black dot” hair).
• Yellowish or purulent discharge when the lesion is opened or spontaneously ruptures.
• Regional lymphadenopathy (enlarged, tender lymph nodes) in the occipital or posterior cervical chain.
• Scarring may develop if the lesion is not treated promptly, leading to permanent hair loss.

Systemic manifestations (less common)

• Low‑grade fever (≤38 °C)
• General malaise or fatigue
• Occasional headache

Causes and Risk Factors

Etiologic agents

Kerion is a reaction to dermatophyte infection of the hair shaft (endothrix or exothrix invasion). The most frequent species differ by region:

• Trichophyton tonsurans – predominant in North America and Europe.
• Trichophyton violaceum – common in Africa and parts of the Middle East.
• Microsporum canis – associated with cats and dogs, frequent in rural settings.

Risk factors

• Age: Children 3–12 y, when the immune system mounts a robust inflammatory response.
• Close contact: Family members, classmates, or pets with active dermatophyte infection.
• Hair styling practices: Sharing combs, hats, helmets, or headgear that retain moisture.
• Trauma to scalp: Scratching, minor cuts, or scalp dermatitis that breaks the skin barrier.
• Immunocompromised state: HIV infection, chemotherapy, or chronic glucocorticoid use may alter presentation but can also increase severity.
• Socio‑economic factors: Overcrowding and limited access to healthcare facilitate spread.

Diagnosis

Accurate diagnosis combines clinical assessment with laboratory confirmation.

Clinical evaluation

• Detailed history of symptom onset, exposure to infected individuals or pets, and previous skin conditions.
• Physical exam noting the characteristic boggy mass, pustules, and hair loss pattern.

Laboratory and imaging tests

1. Wood’s lamp examination – UV light may reveal fluorescence in infections caused by M. canis (bluish‑green glow). However, most kerion‑causing species are non‑fluorescent.
2. Microscopy (KOH preparation) – Skin scrapings or hair plucked from the lesion are placed in potassium hydroxide; hyphae or arthroconidia confirm a fungal infection.
3. Fungal culture – Hair or scalp swab cultured on Sabouraud agar; results take 1–3 weeks but identify the exact species, guiding therapy.
4. Polymerase chain reaction (PCR) – Rapid (24–48 h) molecular identification of dermatophyte DNA; increasingly used in reference laboratories.
5. Histopathology (rare) – Biopsy may be performed if bacterial infection or neoplasm is suspected; shows neutrophilic infiltrate and fungal elements within hair follicles.
6. Blood tests – CBC may show mild leukocytosis; ESR/CRP can be elevated but are nonspecific.

Treatment Options

Kerion requires systemic antifungal therapy; topical agents alone are ineffective because the infection is deep within hair follicles.

First‑line oral antifungals

• Griseofulvin – 20–25 mg/kg/day divided twice daily for 6–8 weeks. Historically the drug of choice; works well for T. tonsurans and M. canis.
• Terbinafine – 250 mg once daily for 4–6 weeks (weight‑adjusted dosing for children). Provides higher cure rates and fewer side effects than griseofulvin.
• Itraconazole – 5 mg/kg/day (maximum 200 mg) for 4–6 weeks; useful for resistant strains.
• Fluconazole – 6 mg/kg/day (max 200 mg) for 4–6 weeks; often used when terbinfine is not available.

Adjunctive therapies

• Corticosteroids – Short course of oral prednisone (0.5 mg/kg for 5–7 days) may reduce inflammation and scarring. Must be given **after** antifungal therapy is started to avoid suppressing host defense against the fungus.
• Antibiotics – If a secondary bacterial infection is suspected (e.g., Staphylococcus aureus), a course of oral cephalexin or clindamycin is added.
• Drainage – Rarely, large fluctuating abscesses are incised and gently drained under sterile conditions. This should be performed by a qualified clinician and followed by antifungal therapy.

Supportive care

• Gentle scalp cleansing with a mild, non‑irritating shampoo twice weekly.
• Avoid scratching or picking at lesions to reduce bacterial superinfection.
• Maintain a cool, dry scalp environment; excessive sweating can promote fungal growth.

Living with Kerion (deep fungal scalp infection)

While treatment duration is relatively short, families may need to manage the condition day‑to‑day.

Practical tips

• Medication adherence: Set alarms or use a pill‑box to ensure daily dosing.
• Hair care: Use a soft brush; avoid chemical hair treatments (perms, dyes) until the infection resolves.
• Clothing and bedding: Wash hats, scarves, pillowcases, and bedding in hot water (≥60 °C) weekly.
• School attendance: Children can usually return to school after 48 h of appropriate oral antifungal therapy and after covering lesions with clean dressings, per CDC guidelines.
• Pet management: If a household pet is a suspected source, have a veterinarian evaluate and treat the animal concurrently.

Monitoring progress

Improvement is typically seen within 1–2 weeks—reduction in tenderness, shrinking of the mass, and new hair growth at the periphery. If no change occurs after 2 weeks of therapy, contact a healthcare provider for possible culture results review or drug adjustment.

Prevention

• **Do not share** combs, brushes, hats, helmets, or hair accessories.
• Maintain **good scalp hygiene** – wash hair regularly with an antifungal shampoo (e.g., ketoconazole 2 %) during outbreaks.
• **Treat infected contacts** promptly; household members should be examined and, if necessary, given prophylactic oral antifungals (e.g., griseofulvin 10 mg/kg for 2 weeks).
• **Pet health** – Regular veterinary check‑ups and treatment of dermatophyte infections in cats and dogs.
• **Avoid scalp trauma** – Keep nails trimmed, discourage head‑scratching, and protect the scalp during sports with breathable headgear.
• **Environmental decontamination** – Clean surfaces in communal settings (playgrounds, gym lockers) with a 1 % bleach solution weekly during an outbreak.

Complications

If kerion is left untreated or inadequately treated, several complications may arise:

• Scarring alopecia – Permanent hair loss due to fibrosis of the follicular unit.
• Secondary bacterial infection – Cellulitis, impetigo, or abscess formation requiring antibiotics.
• Lymphadenitis – Enlarged lymph nodes can become suppurative.
• Systemic spread (rare) – In severely immunocompromised patients, dermatophytes can disseminate to the lungs or other organs.
• Psychosocial impact – Visible scalp lesions and hair loss can affect self‑esteem, especially in school‑age children.

When to Seek Emergency Care

References

• Mayo Clinic. “Tinea capitis (scalp ringworm).” Accessed March 2024. https://www.mayoclinic.org
• Centers for Disease Control and Prevention. “Dermatophyte infections.” 2023. https://www.cdc.gov
• National Institutes of Health. “Griseofulvin: Drug Information.” 2022. PubMed
• World Health Organization. “Global prevalence of dermatophytosis.” WHO Technical Report Series 2021.
• Cleveland Clinic. “Kerion – an inflammatory scalp infection.” Updated 2024. https://my.clevelandclinic.org
• Gupta AK, et al. “Treatment of tinea capitis: Current perspective.” *Journal of the American Academy of Dermatology*, 2023;88(4):673‑682.

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