It is also sometimes called erythema migrans (without the "chronicum") or "EM". However, this phrase is also used to describe geographic tongue.
In a 1909 meeting of the Swedish Society of Dermatology, Arvid Afzelius first presented research about an expanding, ring-like lesion he had observed. Afzelius published his work 12 years later and speculated that the rash came from the bite of an Ixodes tick, meningitic symptoms and signs in a number of cases and that both sexes were affected. This rash is now known as erythema migrans, the skin rash found in early-stage Lyme disease.
In the 1920s, French physicians Garin and Bujadoux described a patient with meningoencephalitis, painful sensory radiculitis, and erythema migrans following a tick bite, and they postulated the symptoms were due to a spirochetal infection. In the 1940s, German neurologist Alfred Bannwarth described several cases of chronic lymphocytic meningitis and polyradiculoneuritis, some of which were accompanied by erythematous skin lesions.
The EM rash occurs, according to sources, in 80% to 90% of those infected with Borrelia. A systematic review of the medical literature shows that 80% of patients have an expanding EM rash, at the site of the tick bite, although some patients with EM do not recall a tick bite. In endemic areas of the United States homogeneously red rashes are more frequent.
A small group of practitioners disputes the generally accepted incidence of the rash, claiming that it occurs in less than 50% of infections. These practitioners suggest that a condition they call "chronic Lyme" (resembling chronic fatigue syndrome or fibromyalgia) exists in the absence of evidence for Borrelia infection. Their proposed treatment of patients with months or years of antibiotics is opposed by the wider medical community's scientific consensus, since these treatments are potentially dangerous, are not based on diagnoses with objective evidence, and have been shown in clinical trials to be ineffective even when evidence of infection is at hand.