The Central Sensitization Inventory validated and adapted for a Brazilian population: psychometric properties and its relationship with brain-derived neurotrophic factor

Abstract

Objectives

The primary aim was to assess the psychometric properties (including internal consistency, construct validity, reproducibility, and factor structure) of the Central Sensitization Inventory (CSI), adapted and validated for a Brazilian population (CSI-BP). Additionally, we evaluated the relationship between the CSI-BP and the serum brain-derived neurotrophic factor (BDNF) and determined if the symptoms elicited by the CSI-BP discriminate between subjects who do/do not respond to the conditioned pain modulation (CPM) task, as assessed by change in numeric pain scale (0–10) score.

Patients and methods

A cross-sectional study was conducted in a pain clinic in a tertiary teaching hospital. A total of 222 adults with chronic musculoskeletal pain and 63 healthy control subjects completed the CSI-BP and the Brazilian Portuguese pain-catastrophizing scale (BP-PCS). A team of experts translated the CSI according to the international guidelines. Test–retest, item analysis, convergent validity, and factor analysis were performed. Later, a random subsample (n=77) was used to correlate the CSI-BP adjusted index with change in numeric pain-scale score during the CPM task and a BDNF blood sample.

Results

The CSI-BP presented strong psychometric properties (test–retest reliability 0.91, Cronbach’s α=0.91). Confirmatory factor analysis yielded a four-factor structure, supporting the original English version. The CSI-BP adjusted index showed moderate positive correlation with the BP-PCS, and classified more than 80% of patients correctly vs healthy controls. Serum BDNF levels explained 27% of the variation in the CSI-BP adjusted index. Subjects with impairment in the descending modulatory system had higher CSI-BP adjusted index scores than subjects who responded normally to the CPM task: 49.35 (12.1) vs 39.5 (12.33), respectively (P<0.05).

Conclusion

The CSI-BP was found to be a psychometrically strong and reliable instrument, with primary evidence of validity. Higher scores on the CSI-BP were correlated positively with serum BDNF and with greater dysfunction of the descending pain-modulatory system.

Keywords:

• confirmatory factor analysis
• cross-cultural adaptation
• conditioned pain modulation
• serum brain-derived neurotrophic factor
• central sensitization
• chronic pain

Supplementary material

Phase I: translation, synthesis, and back-translation

Translation

The original English version of the Central Sensitization Inventory (CSI) was translated into Brazilian Portuguese. Cross-cultural adaptation was carried out by previously published guidelines.^1–3 Four native Brazilian Portuguese speakers carried out independent translations of the pain-catastrophizing scale from English to Brazilian Portuguese: a professional translator, a psychologist, a physician with pain specialization, and a linguist. Forward-translations were compared with one another and with the original English version. After discussing any discrepancies, the four versions were combined into one Brazilian Portuguese version.

Several items were difficult to translate between English and Brazilian Portuguese. For item 3 (anxiety attacks), we decided to use the term “crises”. For item 11, “discomfort in the bladder” was modified to “discomfort and burning sensation”. For item 25, “trauma” was amended to “suffering”, because “trauma” in Brazilian Portuguese is more associated with physical lesions.

Back-translation

Two native English speakers translated the original CSI to Brazilian Portuguese and also carried out a back-translation into English. Brazilian Portuguese was their second language. According to the definition of Deyo,⁴ both back-translators were considered bilingual, but they were not familiar with the subject matter of the questionnaire. Any gross inconsistencies or conceptual errors in the content of the translated versions in preparation for the expert committee meeting were corrected by a third bilingual person.

Delphi method to assess semantics and conceptual content of each item

A team of experts assessed each translated CSI item to ensure content validity. The expert committee consisted of one methodologist, one clinical research scientist, and all of the translators and back-translators. This expert panel was responsible for ensuring semantic and idiomatic equivalence and experiential and conceptual equivalence (ie, to address any peculiarities unique to the cultures examined) between the Brazilian Portuguese and English versions of the questionnaire. The committee members and the panel director corresponded by electronic communication. The panel director processed CSI adapted for a Brazilian population (CSI-BP) item information from the committee members and filtered out the relevant content until everyone came to a consensus on the content of each item on the CSI. If a consensus could not be reached on specific items, rounds coordinated by two clinical research scientists with experience in validating instruments were made until they came to a final consensus.⁵ All changes on the CSI-BP items were based on the consensus of members involved in the translation process. Their goal was to assure that each CSI item on the English and Brazilian versions referred to the same underlying concepts and had the same meanings, to produce the best idiomatic and conceptual (rather than merely literal) equivalence. The forward-translations were compared with one another and with the original English version. The forward-translations were compared with the original English version. As a result of this process, a pilot version of the CSI-BP was completed.

Phase II: pretesting of CSI-BP

Assessment of CSI-BP in the pilot version

Thirty medical school employees – half men, half women – who work with chronic pain patients volunteered to evaluate the meaning of the translated questions and the layout of the “prefinal” version of the CSI-BP. In addition, they were interviewed to explore how they understood each of the 25 items. They had an average age of 30.67 (8.89 SD) years and an average of 19.56 formal years of schooling. Each employee’s self-reported comprehension of the items was assessed with a 10 cm visual analogue scale (VAS; from 0 representing unclear to 10 representing entirely clear). The global mean ± SD of comprehension of the 25 questions of CSI was 9.42±1.23.

In addition to the medical school employees, 20 females with fibromyalgia volunteered to evaluate the meaning of the translated CSI-BP questions using the same VAS and interview process as the medical school employees. Their mean ± SD for number of years of formal schooling was 10.41±4.35, and their mean age was 50.77±9.88 years. The global mean ± SD of comprehension of the 25 questions of CSI-BP reported on the VAS was 8.01±1.21.

All feedback from these subjects was evaluated by the translation workgroup (to assess face validity). Based on subject feedback, two questions were slightly modified to achieve the final Brazilian Portuguese version of the CSI-BP. The final version of the CSI-BP is presented at http://dorneuromodulacao.com.br.

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Acknowledgments

This research was supported by grants and material support from the following Brazilian agencies: Committee for the Development of Higher Education Personnel (CAPES - PNPD/CAPES) (grants to LCA) and material support; National Council for Scientific and Technological Development (CNPq) (grants to ILST and WC); Postgraduate Program in Medical Sciences at the School of Medicine of the Federal University of Rio Grande do Sul (material support); Postgraduate Research Group at the Hospital de Clínicas de Porto Alegre (FIPE-HCPA) (material support); and the Brazilian Innovation Agency (FINEP) (process number 1245/13; WC).

Author contributions

All authors made a significant contribution to study concept and design, acquisition of data, or analysis and interpretation of data, drafting or revising the manuscript for important intellectual content, and approval of the final version to be published.

Disclosure

The authors report no conflicts of interest in this work.