Pediatric Sweet syndrome initially misdiagnosed as immunoglobulin a vasculitis: the importance of repeat biopsy.

Sweet syndrome is characterized by tender erythematous plaques, histologically presenting as marked neutrophilic infiltration in the dermis. In general, this syndrome manifests in middle-aged adults, and given its extreme rarity in the pediatric population, it is rarely considered by pediatricians in routine clinical practice, which often leads to misdiagnosis. A 1-year-old girl had developed palpable purpura subsequent to experiencing upper respiratory symptoms, and at a previous hospital, she was preliminarily diagnosed with immunoglobulin A (IgA) vasculitis in the absence of skin biopsy evidence. The purpura developed into refractory hemorrhagic blisters and subsequently became ulcerated. Although intravenous glucocorticoid therapy was initiated, there was no discernable improvement. After being transferred to our hospital, she initially underwent a skin biopsy, which failed to lead to a diagnosis. We tapered the administration of intravenous glucocorticoid and performed a second skin biopsy, retrieving a specimen from a newly affected lesion. The histopathological findings for the second biopsy revealed marked neutrophilic infiltration extending from the dermis to the adipose tissue, with interstitial dermal edema, which met the diagnostic criteria of Sweet syndrome. This case highlights the importance of prioritizing early diagnostic biopsy prior to initiating empiric therapy when atypical cutaneous features are observed in suspected individuals.