Erythema Annulare Centrifugum
Erythema annulare centrifugum (EAC) is an idiopathic rash that is classified with the gyrate erythema family. It is believed to be a cutaneous reaction to many different antigenic stimuli, although no firm conclusion on the pathogenesis has been made. It has a characteristic clinical presentation that is easily recognized. The pathology of EAC is also characteristic and helps make the diagnosis by ruling out other conditions. EAC can be a marker of internal malignancy, but most cases, by far, are not associated with an underlying malignancy.
Clinical Findings: EAC often manifests insidiously. It has been reported to occur at any age and has no sexual or racial predilection. It has an unusual and peculiar morphology. The lesions start as small, pink papules that slowly expand. The patches of EAC are pink to red with a slowly expanding border. The peculiar and characteristic finding is the presence of a trailing scale. The leading edge of the rash advances and is followed by a few millimeters of fine trailing scale that continues to track the leading edge. As the rash expands outward, a central area of clearing forms. This central area is flesh colored. In tinea infections, in contrast, the scale represents the leading edge and travels in front of the expanding erythema. The main differential diagnosis is between erythema annulare centrifugum, tinea corporis, and mycosis fungoides. Potassium hydroxide (KOH) examination will rule out a dermatophyte, and a biopsy is required to differentiate EAC from mycosis fungoides.
The rash of EAC can be asymptomatic to severely pruritic. Most cases are mildly pruritic, but the most common complaint is of the unsightly appearance. The trunk is the body area most commonly involved, followed by the extremities. It is rarely seen on the face. Some areas may resolve at the same time that new areas are occurring.
Pathogenesis: The exact etiology of EAC is unknown. It is believed to be a reaction to many different antigenic stimuli. Research has suggested that EAC can be seen as a reaction pattern to an underlying tinea infection; this is thought to be a type IV hypersensitivity reaction. Many causes have been reported, including infections (fungal, bacterial, and viral) and medications, and EAC has been reported in association with many different underlying malignancies.
Histology: Biopsies of EAC lesions should be taken from the advancing border. EAC has a superficial and deep perivascular lymphocytic infiltrate. The infiltrate has a highly characteristic “coat sleeve” appearance around the vessels. The lymphocytic infiltrate is concentrated immediately around the vessels in the dermis, and the lymphocytes appear to be coating the vessel walls.
Treatment: EAC is almost always a self-limited process that spontaneously resolves. If an underlying infection is suspected, treatment and resolution of the infection has been shown to help resolve the rash of EAC. Malignancy-associated EAC is chronic in nature; it tends to resolve with treatment of the malignancy and to recur with relapses. Drug-induced EAC responds to discontinuation of the offending medication. Topical corticosteroids such as triamcinolone may be used to help decrease the erythema and pruritus.