Dermatology MCQ - Inflammatory Dermatoses - Erythema marginatum

A 10-year-old child is admitted to the hospital with fever, migratory arthritis, and a new rash. On examination, you note several non-pruritic, pink, annular and serpiginous macules on the trunk and proximal limbs. A distinctive feature of this rash is that you observe the lesions changing shape and even disappearing before your eyes over the course of minutes. This rash is most characteristic of:

A. Erythema multiforme
B. Urticaria
C. Erythema marginatum
D. Erythema chronicum migrans
E. Annular erythema of infancy

Correct Answer: C. Erythema marginatum

Answer & Explanation

Explanation:

The description is classic for Erythema marginatum, which is one of the major Jones criteria for the diagnosis of acute rheumatic fever.

• Key Diagnostic Clues:

  • Clinical Setting: Occurs in the context of acute rheumatic fever, often with associated fever, carditis, arthritis, or chorea.

  • Morphology: Pink or faint red, annular (ring-shaped) or polycyclic (serpiginous) macules. The edges are typically sharp and the centers are clear.

  • Rapid Migration: The most distinctive feature is its evanescent nature. The lesions can change shape and migrate noticeably over minutes to hours.

  • Non-Palpable and Non-Pruritic: The lesions are typically macular (flat) or barely palpable, and they are not itchy. This helps distinguish them from urticaria.

  • Distribution: Primarily on the trunk and proximal limbs, sparing the face.

The other options are incorrect:

• A. Erythema multiforme: Presents with fixed, true target lesions that have a central dusky area or blister. The lesions are stable for days and do not migrate rapidly.

• B. Urticaria: Lesions are pruritic wheals (edematous, palpable plaques) that also migrate and resolve within 24 hours. However, urticaria is characterized by itching and palpable swelling, whereas erythema marginatum is typically non-pruritic and macular.

• D. Erythema chronicum migrans: This is the rash of Lyme disease. It is a solitary, slowly expanding annular plaque that grows over days, not a multifocal rash that changes shape within minutes.

• E. Annular erythema of infancy: This is a benign condition of infants with migrating annular lesions, but it is not associated with systemic illness like rheumatic fever. The timing (age 10) and associated symptoms make this diagnosis highly unlikely.

Key Associations for Erythema Marginatum

• Pathophysiology: It is thought to be a hypersensitivity reaction associated with the immune response to a preceding group A Streptococcus pyogenes infection. It is not a direct infection of the skin.

• Associated Condition: It is one of the Major Jones Criteria for Acute Rheumatic Fever. Its presence, along with other criteria (e.g., carditis, polyarthritis, chorea, subcutaneous nodules), strongly supports the diagnosis.

• Differential Diagnosis: The main differential is urticaria. The key distinguishing feature is that urticaria is pruritic and consists of wheals (hives), while erythema marginatum is non-pruritic and macular.

• Histopathology: Nonspecific. A mild perivascular infiltrate with neutrophils may be seen, but a biopsy is rarely performed as the diagnosis is clinical.

• Prognosis: The prognosis is that of the underlying acute rheumatic fever, which can lead to chronic, progressive rheumatic heart disease if carditis is present.

• Management: Treatment is directed at the acute rheumatic fever with anti-inflammatory medications (e.g., aspirin, corticosteroids) and eradication of the streptococcal infection with antibiotics. Long-term antibiotic prophylaxis is required to prevent recurrent episodes.