Dermatology · Fungal Infections
The facts most likely to be tested
Trichophyton tonsurans is the most common causative organism of tinea capitis in the United States.
Physical examination reveals scaly patches with alopecia and characteristic black dot appearance due to hair shafts breaking at the scalp surface.
Kerion formation is a severe inflammatory response presenting as a boggy, tender, indurated mass that requires systemic therapy to prevent permanent scarring alopecia.
Oral griseofulvin or oral terbinafine are the first-line systemic treatments for tinea capitis.
Topical antifungal agents are ineffective as monotherapy because they cannot penetrate the hair follicle where the dermatophyte resides.
Lymphadenopathy, specifically occipital or posterior cervical nodes, is a classic associated finding in children with tinea capitis.
Wood's lamp examination is only useful for ectothrix infections caused by *Microsporum* species, which will fluoresce bright green.
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A 6-year-old boy is brought to the clinic by his mother due to a persistent rash on his scalp. Physical examination reveals a well-demarcated, scaly patch of hair loss with several broken-off hairs appearing as black dots. There is associated posterior cervical lymphadenopathy. The child has no history of fever or trauma to the area.
What is the most appropriate first-line treatment for this patient?
Oral terbinafine or oral griseofulvin
The clinical presentation of scaly alopecia with black dots and lymphadenopathy is classic for tinea capitis, which requires systemic antifungal therapy because topical agents cannot penetrate the hair follicle.
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Etiology / Epidemiology
Most common in prepubertal children; Trichophyton tonsurans is the primary pathogen in the US.
Clinical Manifestations
Presents as scaly patches with black dot hair shafts and lymphadenopathy.
Diagnosis
Fungal culture is the gold standard; KOH prep is the rapid bedside diagnostic tool.
Treatment
Oral Griseofulvin is the first-line therapy; monitor LFTs during prolonged treatment.
Prognosis
Risk of kerion formation; permanent alopecia if untreated.
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Epidemiology & Etiology
Primarily affects children aged 3–7 years due to close contact and shared fomites. Trichophyton tonsurans accounts for >90% of cases in North America. Transmission occurs via direct contact or contaminated objects like combs and hats.
Pertinent Anatomy
Infection involves the stratum corneum of the scalp and the hair follicle. The fungus invades the hair shaft, leading to structural weakening and breakage at the skin surface.
Pathophysiology
The dermatophyte invades the hair shaft in an endothrix pattern, causing the hair to become brittle. The host immune response triggers local inflammation, scaling, and potential secondary bacterial infection.
Clinical Manifestations
Classic presentation includes scaly patches of alopecia with black dot appearance from broken hairs. Patients may present with occipital lymphadenopathy. A kerion—a boggy, inflammatory mass—is a severe complication that requires prompt treatment to prevent scarring.
Diagnosis
The fungal culture of hair/scalp scrapings is the gold standard for definitive diagnosis. A KOH prep showing hyphae or spores is the rapid diagnostic test. A Wood's lamp examination is rarely useful today as most modern strains do not fluoresce.
Treatment
Systemic therapy is required because topical agents cannot penetrate the hair follicle. Oral Griseofulvin is the first-line treatment. Hepatotoxicity is a major concern, requiring baseline and periodic LFT monitoring. Terbinafine is an alternative for specific strains.
Prognosis
Early diagnosis prevents permanent cicatricial alopecia. Patients must be monitored for the development of a kerion, which may require systemic corticosteroids to reduce inflammation and scarring risk.
Differential Diagnosis
Seborrheic dermatitis: greasy yellow scales without hair loss
Alopecia areata: smooth, non-scaly patches of hair loss
Psoriasis: silvery scales with underlying erythema
Trichotillomania: irregular hair lengths with normal scalp skin
Bacterial folliculitis: pustules with surrounding erythema