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.
