Cutaneous/systemic plasmacytosis (C/SP) is a plasma cell disorder characterized by reddish-brown patches, lymphadenopathy, and hypergammaglobulinemia. The degree to which C/SP overlaps with other plasma cell proliferative disorders and neoplasms is incompletely understood. We present the case of a patient with a several-year history of cutaneous plasmacytosis and evidence of systemic involvement with concurrent idiopathic multicentric Castleman disease (iMCD) involving a lymph node. There have been only a few reports of systemic iMCD preceded by a long, asymptomatic phase of cutaneous manifestations. We discuss the relationship between C/SP and iMCD and elaborate on the pathophysiological overlap of these 2 conditions and potential similarities in their pathogenesis. We suggest that the 2 diseases may represent the same entity presenting on a spectrum, with individuals diagnosed with C/SP at risk for progression to iMCD.

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A healthy 12‐month‐old female presented with relapsing and remitting urticaria since birth that was resistant to treatment with antihistamines. A thorough history revealed extensive rheumatic disease on the father's side of the family, and subsequent genetic testing was positive for a missense variant of NLRP3, indicating cryopyrin‐associated periodic fever syndrome (CAPS). CAPS encompasses a spectrum of diseases, all related to a defect in the same gene; manifestations vary in severity and presentation, but most are associated with recurrent rash and fever. Because the patient's only presenting symptom was rash, this case highlights the importance of having a high index of suspicion for cryopyrin‐associated periodic fever syndrome in infants with persistent, early urticaria.