What is kerion?

Dermatophyte fungi such as Trichophyton spp. and Microsporum spp can cause infections of the scalp hair known as Tinea capitis ( commonly ringworm).¹ Kerion is a severe inflammatory form with a hypersensitivity reaction against dermatophytes, which is characterised by painful, pus-filled lesions on the scalp.¹ Usually affecting children, it can also be diagnosed in adults. The inflammation can lead to follicular destruction leading to scarring of the scalp and hair loss.² Timely and accurate diagnosis is essential to prevent irreversible damage and scarring alopecia. Kerion can mimic other scalp conditions, leading to misdiagnosis and delayed treatment. Healthcare providers should maintain a high index of suspicion in patients presenting with inflammatory scalp lesions to ensure favourable outcomes.³

What are the clinical features of kerion?

The most commonly identified presentations of kerion involve:

• lesion appearance: raised, boggy swelling, purulent, painful scalp lesions almost a honeycomb appearance⁴
• alopecia
• crusting pustules, change in skin colour of the scalp usually redness and warm⁴
• occasionally fever and swelling of the lymph nodes
• secondary bacterial infections are common
• presenting in children ages 3 - 14- rarely seen in adults^5,6

What is the differential diagnosis of kerion?

The lack of standardised guidelines for diagnosing Kerion can cause delays in accurate diagnosis and the delivery of treatment.⁴ Typically, diagnosis is based on clinical suspicion. Further confirmation is carried out through lesion culture or microscopic identification using direct testing with potassium hydroxide preparation (KOH).⁴ There are numerous conditions that are often considered as the etiology in the early stages of Kerion diagnosis which include:

• Bacterial abscess
• Scalp psoriasis or infected eczema
• Alopecia areata- hair is lost from some or all of the body
• Dissecting cellulitis - a chronic inflammatory condition of the scalp
• Trichotillomania- compulsive hair-pulling disorder
• Secondary syphilis
• Systemic lupus erythematosus- an autoimmune condition where the immune system attacks healthy bodily tissues
• Skin infections or pyoderma: characterised by pus-filled lesions example impetigo
• Seborrheic dermatitis: long-term skin disorder with flaky, scaley, greasy skin⁶

What is noted on clinical evaluation prior to a diagnosis of kerion?

Clinical evaluation usually begins with a detailed history including onset, symptoms and whether the patient has had exposure to pets/farm animals. Following this, a thorough physical exam is performed by the healthcare provider, which accesses lesion characteristics, hair shaft integrity and regional nodes. The key physical features noted in the clinical examination include:

• Scalp lesions
• Crusting pustules
• Hair loss
• Lymph node enlargement 
• Fever and malaise

What diagnostic tools are available to diagnose kerion?

The initial stages of kerion diagnosis can often be challenging due to high rates of false-negative mycological samples in early-stage analysis. The below methods are used in combination to confirm a diagnosis.

A. Wood's Lamp

This technique uses ultraviolet light to detect fluorescence in certain fungal infections. Some dermatophytes, like Microsporum species which progress to kerion, fluoresce under UV light, aiding in diagnosis. However, not all dermatophytes fluoresce.⁷

B. Direct Microscopy (Potassium Hydroxide or KOH preparation)

A sample of hair or scalp scraping is treated with KOH solution. It is reviewed under a microscope. By dissolving keratin, this test helps detect fungal elements and fungal hyphae become more visible.²

C. Fungal Culture

Samples from the affected area are cultured to specific fungal media. Fungi are slow-growing and could take 2 – 4 weeks to yield results. This is a specific test where growth enables the precise identification of the species involved. It can confirm kerion if the causative dermatophyte species Trichophyton, and Microsporum are identified.²

D. Dermatoscopy (Trichoscopy)

This technique is noninvasive for the patient. It is an imaging method that allows visualization of hair and scalp structures. In kerion, dermoscopy may reveal specific patterns such as “comma hairs,” “corkscrew hairs,” black dots and yellow crusts, which support the diagnosis.⁹

E. Skin Biopsy (rare)

Used when diagnosis remains unclear; a skin biopsy may be performed to examine the tissue histologically and rule out other conditions.¹⁰

F. Molecular Methods

Techniques including polymerase chain reaction (PCR) can detect fungal DNA, offering rapid and specific identification. These methods are particularly useful when traditional cultures are inconclusive.¹

G. Bacterial Culture

Often performed if a secondary infection is suspected.

Why is a combined approach to kerion diagnosis so important?

A combined diagnostic approach plays an important role in accurately identifying kerion.

• Initial clinical assessment involves a thorough examination to identify chief characteristics that can guide us to an initial diagnosis of Kerion
• Laboratory confirmation, namely dermoscopy and other mycological studies enhances the clinician's ability to differentiate kerion from other scalp disorders 

This strategy strengthens diagnostic accuracy and reduces the chance of misdiagnosis. This approach ensures timely and appropriate antifungal treatment is prescribed and thereby reduces the risk of complications such as permanent hair loss and scarring.

Summary 

Diagnosing kerion—a severe inflammatory form of tinea capitis—requires early, combined clinical assessment and laboratory investigations to ensure accurate identification and prompt treatment, thereby minimizing long-term sequelae such as scarring and permanent hair loss.