Several skin conditions produce annular lesions. These may be confusing.
Dermatophytosis is the most common, certainly in general practice. Pragmatically lesions which look like it and behave like it are likely to be treated with an antifungal agent such as terbinafine, usually topically but in severe cases or diagnosed and intransigent cases orally. Granuloma annulare may mimic it but has no fluorescence and does not grow fungus in skin scrapings or show hyphae on microscopy in Potassium hydroxide.
Clinical photography has an obvious role in following the development of difficult lesions, and since "difficult" is usually a retrospectoscopic diagnosis photographing lesions should probably be done more often.
This article is a stub. Please feel free to expand it and make it more encyclopaedic.