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

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.