DOLORisk: study protocol for a multi-centre observational study to understand the risk factors and determinants of neuropathic pain by Pascal, M, Themistocleous, AC, Baron, R, Binder, A, Bouhassira, D, Crombez, G, Finnerup, NB, Gierthmühlen, J, Granovksy, Y, Groop, L, Hebert, HL, Jensen, TS, Johnsen, K, McCarthy, MI, Meng, W, Palmer, CNA, Rice, ASC, Serra, J, Solà, R, Yarnitsky, D, Smith, BH, Attal, N, Bennett, DLH