Tinea and fungal skin infection — branching viva

Opening — framing the problem

The examiner begins: a five-year-old has a three-week history of an itchy, scaly bald patch on the scalp with broken hair stubs, black dots flush with the skin and an enlarged occipital node. Talk me through your approach. ^[1]

I would frame this as tinea capitis. The broken hair stubs and black dots are hair broken flush with the scalp surface, which is the endothrix pattern of Trichophyton tonsurans, and the enlarged occipital node favours a fungal scalp infection over a non-infectious dermatosis. I would confirm with potassium hydroxide microscopy of a plucked hair looking for branching septate hyphae and arthroconidia, and send fungal culture to identify the species. ^[1]