Acrodermatitis chronica atrophicans (ACA) is a skin rash indicative of the third or late stage of European Lyme borreliosis.

ACA is a dermatological condition that takes a chronically progressive course and finally leads to a widespread atrophy of the skin.

This progressive skin process is due to the effect of continuing active infection with the spirochete Borrelia afzelii, which is the predominant pathophysiology.

It begins with an inflammatory stage with bluish red discoloration and cutaneous swelling, and concludes several months or years later with an atrophic phase.

Other methods include microscopy and culture (in modified Kelly's medium) of skin biopsy or blood samples.