What is an Erythema Migrans (EM)?
The Erythema Migrans or EM, commonly referred to as the Lyme disease “bull’s-eye” rash, is considered pathognomonic (or diagnostic) of Lyme disease. This skin rash varies in size and shape; often has expanding rings of varying shades, but can be uniformly discolored. It may be hot to touch, it may even itch. It may change in color from reddish to purple to bruised looking, and it can seldom be necrotic (crusty/oozy). Multiple rashes per bite and multiple rashes not at the site of the bite may indicate disseminated disease. Lyme disease usually begins with an EM rash and flulike symptoms (headache, stiff neck, fever, muscle aches, or fatigue). The EM can appear days to weeks after the bite. However, only 60% of light-skinned patients notice this rash. And recent studies indicate that as many as 40%-55% of people never present with a rash at all, but with a flulike illness as the first sign of onset of LD. If you get an EM after a tickbite (and/or multiple rashes), it is advisable to see
