Background: STAT5 is a transcription factor that is vital for mast cell function. Results: Loss of Fyn kinase prevents, whereas loss of Lyn, Gab2, or SHP-1 enhances, Fc⑀RI-mediated STAT5 tyrosine phosphorylation. Conclusion: IgE-mediated STAT5 activation in mast cells requires Fyn kinase.Significance: Elucidating the mechanisms of mast cell activity is essential to understanding and treating allergic pathologies.

Atopic dermatitis (AD) is a common, chronic pediatric skin disease characterized by intense pruritus and a predominantly type 2 inflammatory response. 1 AD is estimated to affect between 7% and 8.6% of adolescents in the United States. 1 Dupilumab is a monoclonal antibody that binds to the interleukin (IL)-4 receptor alpha subunit, inhibiting the IL-4/IL-13 signaling pathway and thereby decreasing levels of two key type 2 inflammatory cytokines implicated in atopic and allergic disease pathogenesis. 2 It is the only US Food and Drug Administration (FDA)-approved systemic therapy for moderate-to-severe AD and was approved for adults in 2017, for adolescents 12 years and older in 2019, 1 and for children ages 6 years and up as of May 2020.While the most commonly reported adverse reactions in adults and adolescents are injection site reactions and conjunctivitis, 1,2 several studies have reported new onset or acute worsening of head and facial erythema and pruritus after dupilumab therapy in adults, [3][4][5][6][7][8][9][10][11][12][13] and recently, in 7/24 (29%) of children. 14 Clinically, these symptoms are consistent with head and neck dermatitis (HND).The exact etiology of dupilumab-associated HND remains unclear.Hypotheses include that dupilumab unmasks or causes a Malassezia hypersensitivity reaction, 3,14,15 psoriasis or rosacea, 6,8,11 or allergic contact dermatitis (ACD). 3,6,9,10 Here, we describe a series of five adolescent patients with AD who were treated with dupilumab and experienced new onset or an exacerbation of HND. All five patients improved with systemic antifungal therapy.

The Shapiro xanthogranuloma is a histopathologic form of xanthogranuloma that shows closely packed monomorphous cells, which can extend into the subcutaneous fat; it usually lacks routine diagnostic features of xanthogranuloma. Herein we describe two cases of Shapiro xanthogranuloma occurring in a neonate and in an infant, which were initially thought to be hematologic malignancies. One patient's presentation as a "blueberry muffin baby" added to the diagnostic confusion. Pediatric dermatologists, dermatologists, and dermatopathologists need to be aware of the Shapiro xanthogranuloma and its clinicopathologic features to avoid misdiagnosis of a hematopoietic malignancy in neonates and infants.

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