IL6 and pachyonychia congenita: In PC type idiopathic multicentric Castleman disease (PC‐iMCD), overproduction of interleukin‐6 (IL‐6) is deeply involved in the pathogenesis of the disease, which leads to systemic symptoms, such as fever, elevated acute‐phase protein and hypergammaglobulinemia in blood, and sheet‐like PC proliferation in tissues.3, 4