RESUMEN
CONTEXT: The multidimensional nature of the fibromyalgia syndrome means that different instruments need to be used to assess the patients' perception of this constellation of physical and psychological symptoms and their impact on their daily lives. Six questionnaires (Multidimensional Fatigue Inventory MFI, Fibromyalgia Impact Questionnaire FIQ, Multiple Ability Self-report Questionnaire MASQ, State-Trait Anxiety Inventory STAI, Beck Depression Inventory-II BDI-II and Patient Global Impression of Change PGIC) were linguistically validated into 12 languages. METHODS: The standardized cross-cultural adaptation process includes the following steps: forward translation, backward translation, and review of the version by a clinician and comprehension tests on subjects in the target country. RESULTS: Regardless of the instruments and dimensions studied, the same translation and cultural adaptation issues arose: (1) an issue that is strictly related to translation, for example, the word "things" was translated as "something"; (2) literal translation is possible but culturally irrelevant, for example the expression "to walk several blocks", which is a completely abstract concept in Europe, was translated as "to walk for more than one kilometre"; (3) the translation needed to be reformulated or the tense needed to be changed for idiomatic reasons. For example, the present perfect does not exist in German and so the present simple was used in the first version. The imperfect was eventually used with adverbs such as "lately". CONCLUSIONS: Linguistic adaptation was completed according to a recognized and rigorous method allowing for the wide-scale use of these patient-reported outcomes instruments in international studies.