Dermatology MCQ - Inflammatory Dermatoses - Rheumatic fever

A 12-year-old child presents with fever, migratory polyarthritis, and a new heart murmur 3 weeks after a poorly treated episode of streptococcal pharyngitis. During the examination, you note a serpiginous, pink, non-pruritic rash on the trunk that seems to fade and reappear within minutes. What is the name of this cutaneous finding?

A. Erythema Multiforme
B. Erythema Nodosum
C. Erythema Marginatum
D. Erythema Chronicum Migrans
E. Erythema Annulare Centrifugum

Correct Answer: C. Erythema Marginatum

Explanation

This presentation, following a streptococcal infection, is highly suggestive of Acute Rheumatic Fever. The Jones Criteria are used for diagnosis, and the described rash is one of the major criteria.

• Erythema Marginatum: This is the pathognomonic rash of Acute Rheumatic Fever. It is characterized by:

  • Pink or faint red, non-pruritic macules or papules that spread outwards in a serpiginous (snake-like) pattern.

  • A key diagnostic feature is its evanescent nature; the lesions can change shape and fade dramatically within minutes to hours.

  • It is typically located on the trunk and proximal limbs, sparing the face.

Why other options are incorrect

• A. Erythema Multiforme: This is an acute, often self-limited hypersensitivity reaction, classically presenting with "target lesions." It is frequently associated with herpes simplex virus or Mycoplasma pneumoniae infections, not streptococcus.

• B. Erythema Nodosum: This presents as tender, red or violaceous, subcutaneous nodules typically on the shins. It is associated with a wide variety of conditions, including sarcoidosis, inflammatory bowel disease, and infections (but not typically streptococcal pharyngitis in the context of rheumatic fever).

• D. Erythema Chronicum Migrans: This is the pathognomonic rash of Lyme disease. It begins as a red macule or papule at the site of a tick bite and expands over days to weeks to form a large, annular, red plaque with central clearing. It is not evanescent.

• E. Erythema Annulare Centrifugum: This is a reactive erythema characterized by slowly expanding, annular or arciform, erythematous lesions with a characteristic "trailing scale" inside the advancing edge. It is persistent and not evanescent like erythema marginatum.

Key Associations for Rheumatic Fever

• Pathogenesis: A delayed autoimmune sequelae of a Group A β-hemolytic Streptococcal (GAS) pharyngitis. Antibodies directed against the M-protein of the bacterium cross-react with human tissues in the heart, joints, skin, and brain (molecular mimicry).

• Jones Criteria (Revised): Diagnosis requires evidence of a preceding GAS infection plus either 2 major criteria, or 1 major and 2 minor criteria.

  • Major Criteria:

    • Carditis (new heart murmur)

    • Polyarthritis (migratory)

    • Chorea (Sydenham's chorea)

    • Subcutaneous Nodules

    • Erythema Marginatum

  • Minor Criteria: Fever, arthralgia, elevated acute phase reactants (ESR, CRP), prolonged PR interval on ECG.

• Other Cutaneous Finding: Subcutaneous nodules are another major criterion. They are small (0.5-2 cm), firm, painless nodules that appear over bony prominences or extensor tendons, similar to those in rheumatoid arthritis.

• Differential Diagnosis: Includes other causes of fever and arthritis in a child, such as Juvenile Idiopathic Arthritis, Lyme Disease, SLE, and Post-streptococcal Reactive Arthritis.

• Management & Prognosis:

  • Acute Episode: Anti-inflammatory treatment with high-dose aspirin or corticosteroids to control carditis and arthritis.

  • Secondary Prevention: The cornerstone of management is long-term antibiotic prophylaxis (e.g., monthly intramuscular benzathine penicillin G) to prevent recurrent GAS infections and further cardiac damage. The duration depends on the severity of carditis.

  • Prognosis depends almost entirely on the severity of cardiac involvement, which can lead to chronic Rheumatic Heart Disease.