A new case report identifies an infant with annular erythema of infancy (AEI) that was mistaken for systemic mastocytosis (SM) due to elevated serum tryptase levels. The report, published in Pediatric Dermatology, highlights the importance of differentiating AEI and other conditions that can present during infancy.

“The presence of annular erythema carries a broad differential, and in some cases, aberrant laboratory findings may lead to workup for systemic diseases even in the absence of symptoms,” the authors wrote. “Herein, we report a case of AEI mistaken for systemic mastocytosis.”

The case involved a 5-month-old boy who presented with a diffuse erythematous rash of 4-months’ evolution, which was being treated with propranolol. Due to a suspicion of SM, he was referred to the authors’ dermatology clinic.

Read more about SM diagnosis

Prior testing for viral or drug-induced multiforme was negative and he did not improve after propranolol was suspended. A lesional punch biopsy was performed and mast cell staining revealed scattered interstitial cells but no aggregates of mast cells.

The patient was not bothered by the rash and there were no accompanying symptoms. Further testing ruled out neonatal lupus, and due to the lack of Darier sign and no mast cell aggregation, systemic mastocytosis was then also ruled out.

Given the waxing and waning nature of the rash and lack of additional symptoms, a diagnosis of AEI was made. The parents decided not to administer further treatment and at 15 months, the rash was completely resolved.

Although AEI is a benign condition, the authors note the importance of distinguishing it from other conditions that may be less benign. An annular pattern in these patients is a key aspect of achieving an accurate diagnosis and can prevent these young patients from having to undergo further invasive tests such as bone marrow biopsies.  


Kingsley JT, Lee EB, Adams JL. A case of annular erythema of infancy accompanied by elevated tryptase. Pediatr Dermatol. Published online July 20, 2022. doi:10.1111/pde.15037