What is the characteristic rash associated with Lyme disease caused by an Ixodes tick bite?

The characteristic rash associated with Lyme disease, which is transmitted by Ixodes ticks, is erythema chronicum migrans. This rash typically presents as a red, expanding lesion that often resembles a "bull's-eye" pattern, featuring a central clearing surrounded by a red border. The rash usually appears at the site of the tick bite and can expand in size over days or weeks.

Erythema chronicum migrans typically emerges within 7 to 14 days following the tick bite and is often asymptomatic, although some patients may experience accompanying flu-like symptoms such as fever, fatigue, and muscle aches. Early identification of this rash is important for the timely diagnosis and treatment of Lyme disease with appropriate antibiotics.

In contrast, other skin conditions like erythema multiforme, psoriasis, and contact dermatitis do not match the specific characteristics and progression of the rash seen in Lyme disease. Erythema multiforme presents with target lesions but is typically not associated with tick bites. Psoriasis is a chronic skin disorder marked by scaling and red plaques, while contact dermatitis is an inflammatory reaction to allergens or irritants and does not exhibit the distinctive features of erythema chronicum migrans. Thus, the identification of erythema