Dermatology & Pediatrics & Infectious Diseases & Family Medicine
Kerion (inflammatory ringworm of the scalp)
Kerion - from the Greek kerion, meaning «honeycomb» - is the most severe and inflammatory form of scalp ringworm (tinea capitis), resulting from an intense host immune reaction against the antigens of a dermatophyte invading the hair follicles and perifollicular stroma. It presents as a boggy (soft + fluctuating like a fluid-soaked sponge) + purulent (suppurating) + painful + alopecising inflammatory plaque of the scalp, often accompanied by tender regional cervical adenopathy, fever and altered general condition. Unlike dry ringworm (non-inflammatory tinea capitis - scaly + alopecia), kerion is triggered by a type IV (delayed) hypersensitivity reaction of the host against fungal antigens - this intense inflammatory reaction is itself responsible for follicular damage and the risk of permanent scarring alopecia if treatment is delayed. It affects almost exclusively children of prepubertal age (2-14 years) and constitutes a pediatric dermatological therapeutic emergency. Zoophilic dermatophytes (from animals - Microsporum canis + cats and dogs + Trichophyton verrucosum + cattle) and geophilic dermatophytes (from soil - Microsporum gypseum) are the agents most often responsible for kerion, as they trigger a more intense inflammatory reaction than anthropophilic dermatophytes (Trichophyton tonsurans - transmitted from human to human - more often responsible for dry ringworm). Treatment is based on oral systemic antifungals (griseofulvin + terbinafine + itraconazole) - topical antifungals alone are insufficient, as follicular penetration requires systemic treatment. The addition of systemic corticosteroids is recommended by some experts to accelerate resolution of inflammation and reduce the risk of scarring alopecia.
Microbiology, pathophysiology, and clinical presentation
- Etiologic agents, sources of contamination, and pathophysiology of kerion: dermatophytes responsible for scalp ringworm and kerion: anthropophilic dermatophytes (transmitted from human to human - mainly causing dry ringworm): Trichophyton tonsurans : most frequent agent in North America (particularly in African-American and Caribbean communities) → endothrix ringworm (spores inside the hair → hair brittle + easily pulled out) → often dry ringworm → kerion possible but less frequent + Trichophyton violaceum + Microsporum audouinii (rare) → zoophilic dermatophytes (transmitted by animals - trigger intense inflammatory reactions → kerion ++): Microsporum canis: cats + dogs → most frequent zoophilic agent in Quebec → teigne ectothrix (spores outside the hair sheath → brittle hair + fluoresces under Wood's lamp - yellow-green) → intense inflammatory reaction → kerion + Trichophyton mentagrophytes : rabbits + guinea pigs + rodents + Trichophyton verrucosum: cattle + horses → responsible for deep kerions (boggy) + geophilic dermatophytes (originating from the soil - trigger intense inflammatory reactions): Microsporum gypseum: soils → gardening work + contact with soil → kerion sometimes + kerion pathophysiology: invasion of hair follicles by the dermatophyte → penetration into the hair cortex (endothrix) or around the sheath (ectothrix) → production of keratinolytic enzymes (keratinases + proteases) → degradation of keratin → activation of adaptive immunity (CD4+ Th1 T lymphocytes) → type IV delayed hypersensitivity reaction → influx of neutrophils → formation of folliculitis + follicular abscesses → suppuration → this immune reaction is initially protective (it eliminates the fungus) but if excessive → damage to hair follicles → perifollicular fibrosis → risk of permanent scarring alopecia if treated late → kerion represents an immunological battle between the host (intense reaction) and the fungus → antifungal treatment + corticoids (to moderate the reaction) must be initiated rapidly to preserve viable hair follicles + id reaction (trichophytide) : remote allergic reaction → vesicular lesions on hands + feet + or trunk → immune mechanism (no remote infection - no local antifungal treatment at these sites) → regression with systemic antifungal treatment
- Clinical Presentation and Differential Diagnosis: clinical presentation of kerion: single (or multiple) plaque on the scalp → boggy appearance (soft + fluctuating like a soaked sponge) + suppurating (pus drains on pressure or spontaneously from follicular ostia → «honeycomb» appearance) + erythematous + painful to the touch + alopeciating (alopecia of the plaque + peeling of the hair on the lesion) + crusts + scales + size: 2-10 cm in diameter → broken hair remains on the plaque (unlike alopecia areata where the scalp is smooth) + location: scalp preferentially → may involve beard + eyelashes + eyebrows + posterior cervical + suboccipital adenopathies + painful + voluminous → almost constant in kerion → may be the first sign leading to consultation + fever + asthenia (in severe forms) + sometimes : id reaction (trichophytide) at a distance + characteristics depending on the agent: Microsporum canis → yellow-green fluorescence with Wood's lamp (ultraviolet lamp - present in around 50 % of cases of M. canis) → endothrix of T. tonsurans → NO fluorescence + paraclinical work-up: direct mycological examination: hair + scales removed → microscopic examination + potash (KOH) → visualizes spores around (ectothrix) or inside the hair (endothrix) + culture on Sabouraud agar + actidione + chloramphenicol → 2-4 weeks for identification → genus + species specification → guides epidemiology + source + CBC: moderate leukocytosis + sign of systemic inflammation + elevated CRP → differential diagnosis: bacterial scalp abscess: staphylococcus + streptococcus → frank pus + without hair breakage → bacterial culture + furunculosis + bacterial pustular folliculitis → no diffuse alopecic plaque + alopecia areata (alopecia): non-inflammatory + non-purulent + smooth scalp + no broken hair + no adenopathies + centrifugal extension possible + chickenpox + burn scars
Antifungal treatment and management
| Treatment / appearance | Data, methods and results | Key studies and recommendations |
|---|---|---|
| Systemic antifungals — griseofulvin, terbinafine, itraconazole Griseofulvin — terbinafine — itraconazole — fluconazole — treatment duration — dosage by weight — treatment of choice by agent — follow-up — mycological test — fatty foods — adverse effects |
Systemic antifungal treatment - mainstay of kerion treatment: fundamental reminder: topical antifungals alone are INSUFFICIENT → do not penetrate hair follicles to the required depth → oral SYSTEMIC treatment is essential + education: avoid sharing hairbrushes + caps + pillows + during treatment → no systematic school eviction if treatment initiated (AAP + NICE) → antifungal shampoo (ketoconazole 2 % or selenium sulfide 2.5 %) × 2-3/week as a supplement (reduces fungal load and risk of contamination) → griseofulvin : historical antifungal + still widely used + pediatric approved → mechanism: inhibition of fungal tubulin polymerization → mitosis arrest + dosage: micronized griseofulvin 20-25 mg/kg/d PO in 1-2 doses → max 1 g/d → or ultramicronized griseofulvin 10-15 mg/kg/d → take with a fatty meal (increased absorption × 2) → duration: 6-12 weeks (up to 4 weeks after clinical and mycological cure) → efficacy: cure rate 80-95 % for M. canis + less effective for T. tonsurans (sometimes requires higher doses or longer duration) → adverse effects: photosensitivity + headache + GI disorders + drug interactions (CYP3A4 inducing enzyme → reduces efficacy of hormonal contraceptives + warfarin + ciclosporin) + contraindication: pregnancy (teratogenic) → porphyrias → lupus erythematosus; terbinafine: 2nd-generation antifungal → mechanism: inhibition of squalene epoxidase → stops ergosterol synthesis + accumulation of toxic squalene → fungicide → superior to griseofulvin for T. tonsurans → pediatric dosage: 35 kg: 250 mg/d → duration: 4-6 weeks → superior to griseofulvin in terms of treatment duration (shorter) → Chen 2001 - Journal of the American Academy of Dermatology: terbinafine superior to griseofulvin for T. tonsurans + shorter duration → terbinafine is now recommended as 1st-line for T. tonsurans in the USA (AAP 2021) → for M. canis → griseofulvin or itraconazole preferred (terbinafine less effective against Microsporum) → adverse effects: GI disorders + rash + rarely hepatotoxicity (liver workup if prolonged treatment) → monitor CBC if prolonged treatment (neutropenia rare); itraconazole : azole → mechanism: inhibition of fungal cytochrome P450 (14α-demethylase) → cessation of ergosterol synthesis → pediatric dosage: 5 mg/kg/d PO in 1 dose → duration: 4-6 weeks → effective for Microsporum + Trichophyton → alternative to griseofulvin if intolerance → numerous drug interactions (CYP3A4 inhibitor ++ ) → contraindication: congestive heart failure + taken with meals (capsules) → fluconazole: triazole + dosage: 6 mg/kg/d × 2-4 weeks → or pulse protocol (6 mg/kg/week × 4-8 weeks) → alternative if griseofulvin + terbinafine + itraconazole not available or not tolerated → less robust data for ringworm + choice according to causative agent (summary): T. tonsurans: terbinafine (1st line AAP) + or griseofulvin (long-term) → M. canis: griseofulvin + or itraconazole → T. verrucosum: griseofulvin + or itraconazole | Chen 2001 — Journal of the American Academy of Dermatology: terbinafine vs griseofulvin + T. tonsurans → terbinafine superior + shorter duration → drug of choice for T. tonsurans + AAP (American Academy of Pediatrics) 2021: scalp ringworm guidelines + terbinafine first-line for T. tonsurans + griseofulvin if M. canis + NICE 2018: ringworm guidelines + kerion → griseofulvin + terbinafine + itraconazole + British Association of Dermatologists (BAD) 2014: tinea capitis guidelines → kerion → systemic treatment → +/- corticosteroids + Gupta 2005 — Journal of the American Academy of Dermatology: review of systemic antifungals for pediatric ringworm → Seebacher 2007 — Mycoses: kerion → treatment + epidemiology + INESSS Quebec + RAMQ: griseofulvin reimbursed for tinea capitis + terbinafine 250 mg reimbursed + itraconazole reimbursed + Health Canada: griseofulvin + terbinafine + itraconazole approved |
| Systemic corticosteroids, topical care, and supportive measures Prednisone - methylprednisolone - cicatricial alopecia prevention - local care - drainage contraindicated - compresses - drying - home monitoring - contamination - animals - sibling screening - antifungal shampoo - return to school |
Systemic corticoids - reduce inflammation and prevent scarring alopecia: role of corticoids in kerion: excessive immune response (type IV hypersensitivity) is itself destructive to hair follicles → corticoids reduce inflammation + preserve viable follicles → recommendation: prednisone PO 1-2 mg/kg/d × 7-14 days → in association with the systemic antifungal → never as monotherapy (the fungus will continue to proliferate on corticoids alone) → results: faster regression of kerion + reduced pain + reduced adenopathy + possible reduced risk of scarring alopecia (less solid data) → Hussain 2007 - Journal of the European Academy of Dermatology and Venereology : corticosteroids + kerion → reduced inflammation + improved regression → moderate level of evidence → BAD 2014 + NICE 2018 guidelines recommend considering systemic corticosteroids in bulky + painful + kerion with risk of scarring alopecia + local management of kerion: DO NOT incise the kerion (nor drain surgically) → the kerion is NOT a frank bacterial abscess → incision only aggravates the lesion + risk of bacterial superinfection + soft compresses soaked in an antiseptic solution (saline + or mildly diluted chlorhexidine) → maintain local hygiene without trauma → antifungal shampoo (ketoconazole 2 % + or selenium sulfide 2,5 %) × 2-3/week → reduces fungal load + decreases risk of contamination of surroundings → especially in the first few weeks + secondary bacterial superinfection : possible in highly suppurative kerions → staphylococcus + streptococcus → oral antibiotic therapy if documented superinfection (amoxicillin-clavulanate + or cefalexin) → bacterial culture of pus → check on cure: check mycological examination at 6-8 weeks → negative culture = mycological cure → clinical cure often precedes mycological cure; surrounding and public health measures: look for animal source: M. canis → cats + dogs → veterinary examination → antifungal treatment of animal if affected (miconazole lotion + or veterinary griseofulvin) → T. verrucosum → farm animals (cattle + horses) → veterinary report → screening of siblings and close contacts: clinical scalp examination + mycological sampling if symptoms → treatment of symptomatic carriers → asymptomatic carrier children transmit the fungus but require treatment if mycological confirmation + return to school : AAP + Canadian authorities generally recommend NOT to exclude the child from school once systemic treatment is initiated → antifungal shampoo during treatment period → inform school + parents of contacts → school eviction is excessive and not recommended in most guidelines | Hussain 2007 - Journal of the European Academy of Dermatology and Venereology: systemic corticoids + kerion → reduced inflammation + accelerated regression + BAD 2014 (British Association of Dermatologists): tinea capitis guidelines → kerion → systemic corticoids recommended in severe forms + NICE 2018: tinea capitis + kerion → systemic treatment + corticoids if severe + AAP 2021: ringworm + back to school → no exclusion if treatment initiated + Gupta 2005 - JAAD: comprehensive review of childhood ringworm → sources + treatment + screening + Seebacher 2007 - Mycoses: kerion → European epidemiology + treatment + Hay 2017 - Mycoses: tinea capitis → worldwide epidemiology + treatment → recent review + Public Health Agency of Canada (PHAC): tinea capitis + management in the community + SCD (Canadian Dermatology Society): tinea capitis + kerion recommendations in Canada + INESSS Québec + RAMQ: griseofulvin + terbinafine + itraconazole + prednisone → reimbursed in pediatric indications |
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A child with a boggy inflammatory plaque of the scalp with suppuration, cervical adenopathy, and alopecia must be treated urgently with an oral systemic antifungal; topical antifungals alone do not penetrate the hair follicles and are insufficient. the choice of antifungal agent depends on the suspected agent (terbinafine for T. tonsurans / griseofulvin or itraconazole for M. canis). The addition of oral prednisone (1-2 mg/kg/d × 7-14 days) accelerates resolution of inflammation and may reduce the risk of permanent scarring. DO NOT incise the kerion - it is not a bacterial abscess. DO NOT use topical corticoids alone - they aggravate fungal growth.
Situations requiring urgent medical attention
Child 2-12 years old with boggy (soft + fluctuating) scalp plaque + suppuration + broken hair + plaque alopecia + voluminous + tender cervical lymphadenopathy + fever → kerion (severe inflammatory ringworm) → urgent medical consultation → mycological samples (KOH + culture) → immediate oral systemic antifungal without waiting for culture: griseofulvin 20-25 mg/kg/d if M. canis suspected (contact with cat or dog) OR terbinafine if T. tonsurans → prednisone 1 mg/kg/d × 7-14 days if significant inflammation → antifungal shampoo × 2-3/week → DO NOT incise.
Child treated for kerion for 4 weeks with no clinical improvement—persistent inflammation + new suppuration + increasing hair loss → treatment failure → check compliance (griseofulvin with fatty meals?) → reassess mycological culture for species identification + antifungal → if M. canis non-responder → increase griseofulvin dose → or switch to itraconazole → if T. tonsurans → terbinafine → pediatric dermatological consultation → risk of scarring alopecia if prolonged delay.
Child with kerion + diffuse vesicular rash on palms + soles + or trunk without infection of these sites → id reaction (trichophytide) → remote allergic reaction to dermatophyte antigens → NO remote infection → NO local antifungal treatment of id lesions → trichophytide regresses with systemic treatment of kerion → antihistamines if intense pruritus → medical consultation for confirmation.
Consult at Clinique Omicron
Clinique Omicron physicians diagnose kerion clinically (boggy, suppurative, alopecic plaque + cervical lymphadenopathy in children), prescribe mycological samples (KOH + culture), initiate appropriate systemic antifungal treatment based on the suspected agent (griseofulvin + terbinafine + itraconazole), add systemic corticosteroids if the kerion is large or severe, advise on surrounding measures (animal contact + siblings + hygiene), and refer to a pediatric dermatologist if the case is complex or resistant. Consultations are available at several service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
The content of this page is provided for informational purposes only and does not substitute for medical or dermatological advice. Kerion is a therapeutic emergency — delayed treatment carries the risk of permanent scarring alopecia. An oral systemic antifungal is essential — topical treatments alone are insufficient.
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