Australian clinical practice guideline: diagnosis and treatment of idiopathic multicentric Castleman disease

Abstract Idiopathic multicentric Castleman disease (iMCD) is a rare condition. The pathogenesis is incompletely understood; however, interleukin‐6 (IL‐6) is a major mediator. The clinical presentation is heterogeneous, from mild constitutional symptoms to severe multi‐organ failure. The diagnosis is challenging, as it incorporates clinicopathologic criteria and requires careful evaluation to exclude various systemic disorders. Targeting IL‐6 activity forms the cornerstone of modern therapy for iMCD, with siltuximab recommended as first‐line therapy. Rituximab‐based regimens are recommended for second‐line therapy. However, many patients do not achieve adequate responses with limited evidence to guide further therapy. In the context of these substantial challenges, herein we provide a multidisciplinary Australasian clinical practice guideline to characterise clinical and pathological features, summarise treatment pathways and discuss clinical outcomes of the condition. The objective is to develop a multidisciplinary clinical practice guideline in the diagnosis and management of iMCD in Australia.