= Erythema migrans
<Erythema migrans> is an expanding skin lesion associated with early <Lyme disease>, commonly developing near the site of an infected <tick> bite. The name describes the outward enlargement of the affected area, not movement of the entire patch across the body. Its appearance varies: central clearing may create rings, but a uniform expanding patch can also occur.<Signs and Symptoms of Untreated Lyme Disease by CDC>[Early signs, erythema migrans: delayed onset, gradual expansion and varied appearance]{ref}
The time course is part of the observation. Recording the border and size on successive days provides information that a single photograph cannot supply. An immediate small local reaction to a bite and a lesion that enlarges over subsequent days are different patterns. <Erythema migrans> is not present in every <Lyme disease> case, so absence of the familiar bullseye image cannot be equated with absence of <infection>.<Signs and Symptoms of Untreated Lyme Disease by CDC>[Rash frequency and distinction from immediate bite-site irritation]{ref}
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