Updated 2026 Japanese Diagnostic Criteria for Takayasu Arteritis.

Takayasu arteritis (TAK) is a chronic, refractory large-vessel vasculitis designated as a Designated Intractable Disease in Japan. The Japanese diagnostic criteria for TAK, last revised in 2017, have been updated to the 2026 version as part of the Japanese Circulation Society 2026 guidelines on the management of large vessel vasculitis, and are presented here in English for the first time. The revision was conducted through a 3-round modified Delphi process involving a panel of 21 experts, supplemented by email discussion and an in-person meeting. The updated criteria incorporate 3 major changes: new symptoms were added and a qualifying statement introduced in Section A; pulmonary artery involvement was elevated to a main criterion in Section B; and IgG4-related periaortitis, Cogan syndrome, and drug-induced aortitis were added in Section C. These updates reflect advances in imaging technology and international classification frameworks, with an emphasis on improving diagnostic sensitivity to reduce missed diagnoses.