New concepts on erythema annulare centrifugum: a clinical reaction pattern that does not represent a specific clinicopathological entity

Summary Background Erythema annulare centrifugum (EAC) is considered an inflammatory skin disease with unknown aetiology. In most textbooks it is assigned to the incoherent conglomeration of figurate or gyrate erythemas. Objectives To re-evaluate a large cohort of patients with EAC and to assess the evidence for infection with Borrelia. Methods We retrospectively investigated 90 cases with the diagnosis of EAC. Haematoxylin and eosin sections were re-examined and diagnoses were specified; these were then confirmed by clinicopathological correlation. Infection with Borrelia was assessed by focus-floating microscopy and by a Borrelia-specific polymerase chain reaction (PCR). Results Besides a miscellaneous group of annular disorders at times confused with EAC such as urticaria, leucocytoclastic vasculitis and psoriasis (20 of 90; 22%), EAC appeared to serve as a collective term for three main clinicopathological reaction patterns: (i) (tumid) lupus erythematosus (29 of 90; 32%), (ii) spongiotic dermatitides (25 of 90; 28%) and (iii) pseudolymphoma (16 of 90; 18%). In 13 of 16 (81%) cases with a pseudolymphomatous reaction pattern spirochaetes stained positive but were negative in other reaction patterns of EAC as well as in negative controls. These findings were confirmed by a Borrelia-specific PCR which was positive in two of three (67%) of these pseudolymphomatous EAC cases but was negative in all other variants of EAC (none of five) as well as 20 controls. Conclusions We conclude that ‘EAC’ is a clinical reaction pattern that does not represent a specific clinicopathological entity and should lead to consideration of mainly lupus erythematosus, dermatitis and, in some cases, cutaneous Lyme disease.