Harmless, but ultimately annoying skin disease
Granuloma Annulare is a common, harmless, but cosmetically disfiguring skin problem that affects women about 3 times as much as men and most commonly strikes in patients under thirty. It can affect every part of the skin and often appears in more than one location (in the disseminated type) but very rarely appears on faces. Most of the time the upper extremities, especially the hands are affected. It is self-limiting and often will disappear within two years, but has been known to hang around in rare cases for up to ten years.
Due to its characteristic pattern it is rather easy to diagnose: it starts of as a ring of small, mildly reddish-brown firm papules that slowly but surely grows. After some time the centre of said ring will start to sink a bit and become more discoloured, giving the whole affair the classic look of a teacup. Shape and size may vary, but, depending on the location of the lesion it can grow to 5 cm diameter. As the presentation is quite common, it is not hard to come up with the right diagnosis, but it's best to keep some other ring-shaped skin lesions within the differential diagnosis: Discoid Lupus, Erythema Multiforme, early Lyme Disease should at least be pondered about.
Why does it appear? Nobody knows. Viral and autoimmune causes have been suggested, but the truth is that nobody knows. The same goes for treatment: The few studies out there were either inconclusive or didn't have enough patients. The usual suspects have all been tried: steroid injections, anti-inflammatories, immune-suppressants, Isotrentoine, etc. Everything that Dermatologists like to play around with, but nothing works on all patients.
The easiest is probably to just wait for it to go away, but in today's medicine that suggestion will probably get you sued.
Sources: My Dermatology lectures and
'Diagnosis and Management of Granuloma Annulare';
Peggy R. Cyr; American Family Physician, Volume 74, Number 10, November 15, 2006