Erythema migrans

What it means

An expanding erythematous (red) skin lesion, usually round or oval, by definition at least 5 cm in size (in largest diameter).

Erythema migrans develops at the site of the deposition of Borrelia burgdorferi 7 to 14 days (range, 1-36 days) following the detachment of certain Ixodes ticks. The most important differential diagnosis is a localized and transient inflammatory reaction to the bite of an arthropod that is not associated with infection and resolves spontaneously within a day or two, and is usually less than 5 cm in size.

Rare diseases that can present with this1

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Erythema chronicum migrans