What is kerion and what is the recommended management, including first‑line systemic antifungal therapy and the use of oral corticosteroids?

Kerion: Definition and Management

What is Kerion?

Kerion (kerion celsi) is a severe inflammatory variant of tinea capitis presenting as a painful, boggy, inflammatory mass with associated alopecia, studded with pustules and matted with thick crust. 1

• This represents a delayed host inflammatory response to the causative dermatophyte, not a primary bacterial infection (though secondary bacterial infection should be evaluated). 1
• Regional lymphadenopathy is common. 1
• Plaques may be solitary or multiple. 1
• Historically associated with zoophilic, large-spore ectothrix species (e.g., T. mentagrophytes, T. verrucosum), but now increasingly caused by endothrix infections with T. tonsurans or T. violaceum, particularly in urban areas. 1
• Misdiagnosis as bacterial abscess is common—maintain high clinical suspicion. 1

First-Line Systemic Antifungal Therapy

Organism-Directed Treatment Algorithm

Initiate oral systemic antifungal therapy immediately when kerion is identified, without awaiting culture results. 2

For Trichophyton Species (Most Common in Urban Areas):

Terbinafine is the preferred first-line agent due to its fungicidal activity and superior efficacy: 2, 3

• Children <20 kg: 62.5 mg/day for 2-4 weeks 2, 3
• Children 20-40 kg: 125 mg/day for 2-4 weeks 2, 3
• Children >40 kg and adults: 250 mg/day for 2-4 weeks 2, 3
• Advantages include shorter treatment duration (improving compliance) and gastrointestinal disturbances occurring in <8% of children. 2

For Microsporum Species:

Griseofulvin is the preferred first-line agent: 2, 3

• 15-20 mg/kg/day for 6-8 weeks (children <50 kg) 2, 3
• 1 g/day for 6-8 weeks (children >50 kg and adults) 2
• Terbinafine fails against Microsporum because it cannot be incorporated into hair shafts in prepubertal children and doesn't reach the scalp surface where arthroconidia are located. 2

When Organism is Unknown (Empiric Treatment):

• Start treatment immediately if cardinal clinical signs are present (scale, lymphadenopathy, alopecia, or kerion). 2
• Collect specimens via scalp scrapings, hair pluck, brush, or swab for microscopy and culture before initiating therapy. 2, 3
• Consider local epidemiology: T. tonsurans predominates in North America and urban areas, while M. canis is more common with animal exposure. 1, 4

Second-Line Options:

Itraconazole: 5 mg/kg/day for 2-4 weeks or 50-100 mg/day for 4 weeks (effective against both Trichophyton and Microsporum species). 2, 3

Fluconazole: Favorable tolerability profile, available in liquid form, useful for refractory cases. 2, 3

Use of Oral Corticosteroids

The Controversy:

The evidence for oral corticosteroids in kerion is mixed and controversial. 4, 5

• Some experts advocate for corticosteroids to inhibit the host inflammatory response and minimize scarring risk. 4
• However, a 2011 retrospective study concluded that oral and intralesional corticosteroids are an unnecessary adjunct to oral antifungal therapy for children with kerion in urban areas. 5

Practical Recommendation:

Add topical or oral corticosteroids to alleviate severe inflammatory symptoms associated with kerion. 2

• Reserve corticosteroids for the most severe cases with intense inflammation, pain, and risk of scarring. 4
• Consider a short burst of oral corticosteroids (e.g., prednisone 1-2 mg/kg/day for 5-7 days) or topical corticosteroids for less severe cases. 4
• Corticosteroids may improve diagnostic yield: highly inflammatory kerions have significantly higher rates of negative fungal cultures (80% vs. 16.7% for mildly inflammatory kerions), but sampling after combined oral antibiotic and steroid course improved culture positivity (90.9% vs. 18.2% at baseline). 6

Critical Management Principles

Diagnostic Considerations:

• Highly inflammatory kerions are frequently culture-negative (80% false-negative rate) before treatment. 6
• If possible, sample non-inflammatory tinea capitis lesions (when present in addition to kerion) for highest culture sensitivity. 6
• Wood's lamp examination can detect M. canis infections (characteristic fluorescence). 2
• Dermoscopy shows "comma-shaped" hairs in ectothrix infections (white children) or corkscrew hairs (Afro-Caribbean children). 2

Treatment Endpoint:

The endpoint of treatment is mycological cure, not clinical improvement. 2, 3

• Repeat mycology sampling is mandatory until clearance is achieved. 2, 3
• If clinical improvement occurs but mycology remains positive, continue current therapy for an additional 2-4 weeks. 2, 3

Adjunctive Measures:

• Topical antifungal therapy should be used as adjunctive treatment only—never as monotherapy. 2, 3
• Screen all family members and close contacts, especially for T. tonsurans infections. 2, 3
• Cleanse hairbrushes and combs with bleach or 2% sodium hypochlorite solution. 3
• Children receiving appropriate systemic and adjunctive topical therapy can attend school or nursery. 3

Common Pitfalls to Avoid

• Do not use terbinafine for Microsporum infections—it has poor efficacy and leads to treatment failures. 2, 3
• Do not rely on topical therapy alone—it cannot eradicate scalp infections. 2, 3
• Do not underdose griseofulvin—higher doses (20-25 mg/kg/day) are needed due to increasing treatment failures with lower doses. 2, 4
• Do not mistake dermatophytid ("id") reactions for drug reactions—these pruritic papular eruptions (especially around the outer helix of the ear) represent a cell-mediated response to dying dermatophytes after effective therapy initiation and do not warrant cessation of systemic antimycotic therapy. 1, 2
• Do not overlook secondary bacterial infection—while kerion is a fungal-driven inflammatory response, secondary bacterial infection should be evaluated when clinically indicated. 1, 2