Pérez C, Gálvez R, Huelbes S, Insausti J, Bouhassira D, Díaz S, et al. Validity and reliability of the Spanish version of the DN4 (Douleur Neuropathique 4 questions) questionnaire for differential diagnosis of pain syndromes associated to a neuropathic or somatic component. Health Qual Life Outcomes. 2007;5(1):66.