Background
A ‘kerion’ (‘kerion celsi’) refers to an abscess formed secondary to a fungal infection of the skin – ‘tinea’; it is thought to be a complication of an overactive inflammatory response by the body’s immune system. A kerion is most commonly found on the scalp and can be associated with localised hair loss (alopecia).
Tinea is a general term to describe a fungal skin infection, and is classified according to which part of the body is infected. For example tinea capitis (head), tinea cruris (groin) and tinea pedis (foot). One of the top causes of tinea (and hence kerion) worldwide is Microsporum canis, this is spread from animals to humans.
Tinea mostly affects children of primary school age, especially in urban areas. It is less common in adults, but may be seen in the immunocompromised.
Signs & symptoms
A kerion appears as an inflamed, boggy lump (or multiple lumps) that is tender to touch. The overlying skin may ooze or be crusted, with localised alopecia; there is often regional lymphadenopathy. There may be systemic signs of infection such as fevers and nausea.
In some patients, an extensive, itchy erythematous rash may appear – secondary to kerion. This is known as ‘dermatophytide’, a rash caused by an allergic reaction to the fungal infection. However as this dermatophytide rash is not infective in nature, the fungus cannot be isolated from it.
Diagnosis
A thorough history and clinical examination are first required, which may highlight risk factors for a fungal infection such as animal exposure or family members with rashes.
A kerion can be examined under a Wood’s lamp (a special device that emits UV light), which may reveal skin fluorescence secondary to the fungal infection.
Skin scrapings and hair samples can be taken for microscopy to confirm tinea capitis. Fungal culture can also identify the causative agent, however this is slow and can take up to 4 weeks.
Differentials
- Bacterial scalp infection (pyogenic abscess, folliculitis, impetigo)
- Alopecia areata and trichotillomania
- Scalp psoriasis
- Atopic dermatitis, seborrhoeic dermatitis
Management
- Oral antifungals; topical antifungals alone are not sufficient to treat a kerion.
- Family screening; if family members are left untreated this can result in recurrence.
- Thorough cleaning of sheets, towels, hairbrushes etc. (fomites).
- Children should be allowed to attend school if receiving correct oral and topical antifungal treatment.
References
https://dermnetnz.org/topics/kerion/
https://www.bad.org.uk/library-media/