Dermatology MCQ - Inflammatory Dermatoses - Erythema annulare centrifugum

A 35-year-old woman presents with an asymptomatic, slowly expanding, erythematous eruption on her thighs of several weeks' duration. On examination, you find several annular and arcuate plaques with a characteristic trailing scale just behind the advancing, non-scaly red border. The most likely diagnosis is:

A. Tinea corporis
B. Subacute cutaneous lupus erythematosus
C. Erythema migrans
D. Granuloma annulare
E. Erythema annulare centrifugum

Correct Answer: E. Erythema annulare centrifugum

Answer & Explanation

Explanation:

The description provided is the classic presentation for Erythema Annulare Centrifugum (EAC). The key diagnostic clue is the presence of "trailing scale" – a delicate rim of scale found just inside the advancing edge of the erythematous border. This distinguishes it from other annular eruptions.

• Clinical Course: EAC lesions typically expand slowly (over weeks) and can reach a large size. They are often asymptomatic or mildly pruritic.

The other options are incorrect:

• A. Tinea corporis: This also presents with an annular, scaly plaque. However, the scale in tinea is typically at the leading edge of the plaque (the active border), not trailing behind it. A potassium hydroxide (KOH) preparation would be positive for fungal hyphae.

• B. Subacute cutaneous lupus erythematosus (SCLE): This presents with annular or psoriasiform plaques, often in a photodistribution. The scale is usually finer and more diffuse, and the lesions are not typically described as having a "trailing scale." Patients are often ANA and anti-Ro/SSA positive.

• C. Erythema migrans: This is the characteristic rash of Lyme disease. It presents as a rapidly expanding, erythematous, annular patch or plaque, but it classically has central clearing and lacks scale. It is often described as a "bull's-eye" but is not scaly.

• D. Granuloma annulare: This presents with annular, flesh-colored to erythematous plaques composed of firm papules. It is non-scaly, and the border is typically smooth and firm upon palpation.

Key Associations for Erythema Annulare Centrifugum

• Pathophysiology: The exact cause is unknown, but it is considered a reactive hypersensitivity reaction. It is often idiopathic but can be associated with underlying triggers.

• Associated Conditions / Triggers:

  • Infections: (e.g., dermatophytosis, candidiasis, EBV, helminths) – it is thought to be a "id" reaction in some cases.

  • Malignancy: In older adults, EAC can be a paraneoplastic phenomenon, associated with hematologic malignancies and solid tumors.

  • Drugs: Certain medications have been implicated.

  • Endocrine Disorders: (e.g., thyroid disease).

• Histopathology: A superficial and deep perivascular lymphocytic infiltrate ("coat-sleeve" distribution) is characteristic. The epidermis may show mild spongiosis and focal scale-crust (corresponding to the trailing scale).

• Differential Diagnosis: The main differential is other "gyrate erythemas," which include erythema marginatum (associated with rheumatic fever) and erythema gyratum repens (a dramatic, wood-grain-like eruption that is almost always paraneoplastic).

• Prognosis: The course is variable. Individual lesions can persist for months to years, and the overall condition may resolve spontaneously or recur intermittently.

• Management:

  1. Search for a Trigger: A careful history and appropriate workup for underlying infection, malignancy (especially in older adults with new-onset EAC), or other associated conditions is paramount.

  2. Symptomatic Treatment: If no cause is found, treatment is often unsatisfactory. Mid-potency topical corticosteroids may help with pruritus and inflammation, but they rarely clear the eruption. Systemic agents like antihistamines or oral corticosteroids can be tried for severe or widespread cases.