Erythema migrans
From Wikipedia, the free encyclopedia
Erythema migrans (EM), formerly called erythema chronicum migrans, refers to the rash often (though not always) seen in the early stage of Lyme disease. It can appear anywhere from one day to one month after a tick bite. The EM rash does not represent an allergic reaction to the bite, but rather an actual skin infection with the Lyme bacteria. A physician-identified EM rash warrants a diagnosis of Lyme disease and immediate treatment without further testing, even by the strict criteria of the Centers for Disease Control.
[edit] Description
Erythema migrans is an expanding red rash, usually round or oval in shape, but varying greatly in size and appearance. Though the rash often expands to several inches or more in diameter, it can also appear much smaller (the Lyme bacteria have been cultured from EM rashes less than 5 cm, termed "mini EM"). It may be uniformly red, there may be central clearing ("bull's-eye"), or the center may be redder than the periphery. The rash is often warm to the touch, and it may be itchy and/or painful.
