An international multispecialty validation study of the IgG4‐related disease responder index by Wallace, ZS, Khosroshahi, A, Carruthers, MD, Perugino, CA, Choi, H, Campochiaro, C, Culver, EL, Cortazar, F, Della-Torre, E, Ebbo, M, Fernandes, A, Frulloni, L, Hart, PA, Karadag, O, Kawa, S, Kawano, M, Kim, M-H, Lanzillotta, M, Matsui, S, Okazaki, K, Ryu, JH, Saeki, T, Schleinitz, N, Tanasa, P, Umehara, H, Webster, G, Zhang, W, Stone, JH