Fungal infection of the skin is caused predominantly by dermatophytes (also known as ringworm or tinea). It commonly presents on the foot (Athlete’s foot), scalp (tinea capitis) and groin but can present anywhere on the body.
Dermatophytes are are group of fungal organisms (incorporating Epidermophyton, Microsporum and Trichophyton) which inhabit the keratin layer of the epidermis (i.e. the dead layer). Although they can release enzymes which can promote deeper invasion, this is usually prevented by host defenses. They instead invade peripherally outwards, producing a ring like lesion. At the periphery, there is often increased skin proliferation in response to the infection, which may result in scaling and itch. In the centre, the skin is left to heal and can be normal.
- Classically present with an itchy, annular (ring-like) rash
- Usually red/pink and scaly at the border, and normal colour in the centre
- May be flat with the skin or raised (may resemble a plaque)
- Occasionally can be vesicular/pustular (vesiculobullous tinea)
- Most common places to be affected are the groin, skin folds and feet (which can either be interdigital or ‘mocassin’ distribution)
- Another common area is the scalp- in which scalp scaling, patchy/irregular hair loss and itch (NB exclude seborrhoeic dermatitis – no hair loss; and psoriasis – more scaling)
- Nail infections commonly present with onycholysis and nail dystrophy but won’t often be itchy
- If you suspect tinea as a cause, then skin scrapings for fungal hyphae are the first line investigation
- NB Wood’s lamp test may be useful in scalp infections (tinea capitis) but not in that of the body
- These infections can be mistaken for eczema and psoriasis. Topical steroids used to treat eczema can often mask the symptoms of tinea infection (tinea incognito).
- Ultimately, the diagnosis is a clinical one
- Treatment with a topical imidazole (e.g. clotrimazole) is first line. If the itch is severe, then the use of combined antifungal and steroid treatment can be used (e.g. trimovate)
- Scalp infections should be treated with an oral antifungal (e.g. griseofulvin or terbinafine).