Tinea is an infection of keratinised tissues, including skin, hair, or nails, caused by a group of fungi known as dermatophytes. It is a common presentation in children and young people, but differential diagnosis can be challenging.
Pictures and information courtesy of Timothy G Berger MD Source: The Dermatology Glossary, UCSF School of medicine
Tinea may infect various parts of the body and is termed accordingly, eg:
- Tinea capitis (scalp)
- Tinea corporis (body)
- Tinea cruris (groin)
- Tinea pedis (feet)
- Tinea manuum (hand)
- Tinea faciale (face)
- Tinea unguium (nails)
- Tinea versicolor (trunk)
The usual distribution for tinea versicolor is that of a short-sleeved turtleneck sweater – neck, trunk, upper arms. The responsible organism is the yeast Pityrosporum orbiculare (called Malassezia furfur when in the infectious hyphal form). Fungal enzymes produce compounds that inhibit melanin production. Often the lesions are asymptomatic and patients become aware of the lesions because affected areas do not tan.
The test involves vigorous scraping of scale from the edge of a scaling lesion. If vesicles or pustules are being tested, the underside of the vesicle is sampled. The scraping is deposited onto a glass slide and a drop of 10 to 20% KOH is added before covering with the cover slip. The undersurface of the slide is gently heated before microscopic examination. Under 100X magnification, the entire cover slip is scanned for the presence of hyphae which are thread-like branching tubular cells interconnected by septa.
Microscopically, a KOH preparation shows a combination of fungal hyphae and yeast forms in a “spaghetti and meatballs” appearance within the superficial layers of the epidermis.
Microscopically there are septate fungal hyphae in the superficial layers of epidermis which are more easily demonstrated with PAS (periodic acid Schiff) stains that stain fungal hyphae walls. The epidermis may show hyperkeratosis with variable neutrophil infiltrates and spongiosis. The dermis may have a mixed inflammatory infiltrate and tinea can cause subepidermal bulla Formation. Speciation of fungi is not reliable by simple microscopic methods and is not needed for therapy.