Dermatology MCQ - Inflammatory Dermatoses - Annular erythema of infancy

A healthy 9-month-old male infant is brought to clinic for an evaluation of a recurrent rash. The mother describes transient, pink, annular and arciform patches that appear mainly on the trunk and limbs. The individual lesions expand and migrate over a few hours and resolve without scaling or crusting within 24 hours. The infant is otherwise well, afebrile, and meeting developmental milestones. The most likely diagnosis is:

A. Urticaria
B. Neonatal lupus erythematosus
C. Erythema migrans
D. Erythema annulare centrifugum
E. Annular erythema of infancy

Correct Answer: E. Annular erythema of infancy

Answer & Explanation

Explanation:

The presentation is classic for Annular Erythema of Infancy (AEI), now often classified under the spectrum of Benign Annular Erythemas of Infancy.

• Key Diagnostic Clues:

  • Age: Onset in infancy (typically before 12 months).

  • Lesion Morphology: Annular, arcuate, or polycyclic pink or red patches.

  • Rapid Evolution: Lesions can change shape and migrate within hours, distinguishing them from the slower-moving erythema annulare centrifugum.

  • Transience: Individual lesions resolve completely within 24 hours, similar to urticaria, but they are typically non-pruritic.

  • Lack of Scale/Crust: The lesions resolve without any secondary changes.

  • Well Infant: The child is otherwise entirely healthy, which is a critical positive finding.

The other options are incorrect:

• A. Urticaria: While urticarial wheals are also transient (<24 hours), they are typically pruritic and have a more whealed, edematous center. AEI lesions are often macular (flat) or only slightly raised and are notably non-pruritic.

• B. Neonatal lupus erythematosus (NLE): This presents with annular or polycyclic erythematous plaques, often with scale and/or central atrophy. They are typically photodistributed (face, scalp), are not transient, and are associated with maternal anti-Ro/SSA and anti-La/SSB antibodies. The infant may have systemic manifestations (e.g., congenital heart block).

• C. Erythema migrans: This is the rash of Lyme disease, which is an expanding annular erythema. However, it is not transient; it persists and expands over days to weeks. It would be exceptionally rare in a non-ambulatory infant and requires a tick bite.

• D. Erythema annulare centrifugum (EAC): This is a condition of adults (rarely older children) characterized by lesions that expand slowly over days to weeks and have a characteristic "trailing scale" inside the advancing border, which is absent in this case.

Key Associations for Annular Erythema of Infancy

• Pathophysiology: The cause is unknown. It is considered a benign, reactive phenomenon, possibly a unique hypersensitivity response in infant skin.

• Clinical Presentation: The eruption is characterized by its recurrent, migratory nature. New lesions appear as old ones fade. It is often confused with urticaria but is distinguished by the lack of pruritus and the more macular, serpiginous morphology.

• Differential Diagnosis: The main differentials, as listed above, are urticaria and neonatal lupus. A careful history and physical exam are usually sufficient to distinguish it.

• Histopathology: Nonspecific. A superficial perivascular lymphohistiocytic infiltrate may be seen, but a biopsy is rarely indicated or performed given the classic clinical presentation.

• Prognosis: Excellent. This is a self-limited condition. It typically resolves spontaneously without sequelae, usually within several months to a few years.

• Management: Primarily reassurance. No treatment is necessary. Parents should be educated that the condition is benign, resolves on its own, and does not cause the infant any discomfort. Topical treatments are ineffective and not recommended.