Erythema annulare centrifugum (EAC) is a rare dermatological reaction that initially presents as an urticaria-like papule or plaque. This erythematous lesion enlarges centrifugally and clears centrally, frequently exhibiting scaling along the inner portion of the advancing edge (e.g., trailing scale). Annular plaques can cause pruritus and appear in serpiginous, gyrate, or polycyclic patterns. The etiology behind EAC is incompletely understood, although its occurrence has been associated with various conditions, including drug reactions, fungal infections, food allergy reactions, autoimmune disorders, and stress [1- 2].

EAC can occur in patients of all ages, although it is most commonly reported in adults 40 years or older. Moreover, it most frequently affects the buttocks, arms, and thighs, although it can be found in any body location. Diagnosis of EAC can be achieved based on physical examination alone if the characteristic trailing scale is present or in conjunction with histological findings. Histopathologically, EAC can manifest as two variants: superficial and deep [2]. Superficial EAC is characterized by superficial perivascular lymphocytic infiltration accompanied with dermal edema. These findings may or may not be accompanied by epidermal changes, including hyperkeratosis, spongiosis, parakeratosis, or crusting. Contrastingly, while deep EAC manifests as superficial and deep dermal perivascular lymphocytic cuffing, it is not accompanied by epidermal changes [2].

Most cases of EAC are idiopathic or a result of a hypersensitivity to the aforementioned conditions. Currently, there is no standard of care for EAC, and treatment often involves the discontinuation of known contributors. Topical steroids and antihistamines, which may provide some relief in cases of psoriasis, are typically ineffective for treating EAC, as relapse is common following their discontinuation [3]. Systemic administration of prednisone, etanercept,3 and doxycycline4 have been shown to elicit resolution of cutaneous findings, although relapse is also likely following drug discontinuation.

The case we report in this article suggests that diagnosis of EAC based on physical examination alone should be corroborated with histological findings, for other skin conditions can manifest as EAC. Namely, skin eruptions that can present as EAC include hypereosinophilic dermatitis [4], bullous pemphigoid [5], secondary syphilis [6], pityrosporum infection [7], pustular psoriasis [8] and acute-eruptive psoriasis [9].

Psoriasis is a skin condition whose etiology is multifactorial. Although the diagnosis of psoriasis can also be made based on the clinical presentation of its classical features, in rare instances, psoriasis can masquerade as different skin conditions and thus complicate its diagnosis. EAC-like psoriasis was first reported in 1933 by Milian and Katchoura and later by Lapiere in 1959, subsequently leading to the term EAC-type psoriasis (EACP) [9,10]. EACP may be easily misdiagnosed given its varied clinical histopathological presentations. Clinical features may or may not involve the presence of annular and circinate plaques with peripheral pustulation, scabbing, or scaling collarettes and do not necessitate a medical history of psoriasis. Histologically, EACP ordinarily showcases polymorphonuclear microabscesses, spongiform pustules, and neutrophil infiltration in the epidermis. Still, these may not be present in all cases and may also vary in severity or intensity [10].

EACP is transient and may reoccur cyclically. It is responsive to topical therapy (i.e., topical 0.1% triamcinolone cream or mometasone ointment, as presented in this case) and retinoids. However, more severe cases may benefit from systemic administration of corticosteroids [9,10]. Patients who suffer from comorbid conditions and require chronic administration of other medications (i.e., antineoplastic agents, antihypertensive drugs, etc.) may not be responsive to antipsoriatic treatments like retinoids, cyclosporine A, PUVA, or topical therapies that usually help relieve EACP symptoms [10]. In these instances, patients have been shown to benefit from the replacement or discontinuation of previous medication and combinatorial treatment with methotrexate, acitretin, and topical calcitriol. In general, though, medical professionals should alter the concentrations of current medications to ensure they are well tolerated by the patient.