Study sample
A sample of MS patients based on the McDonald criteria (McDonalds et al. 2001) in the clinical types Relapsing-Remitting (RRMS), Primary Progressive (PPMS) and Secondary Progressive (SPMS), who were visited at the Multiple Sclerosis outpatient Clinic of Hospital of Lagoa, Rio de Janeiro, Brazil, were recruited to this study between August 2009 and June 2010.
Patients with other idiopathic demyelinating diseases; patients with no confirmed MS diagnosis; patients in an acute relapse; and patients incapable of verbal communication were excluded from this study. The authors of the original version of the DYMUS questionnaire authorized the translation and cross-cultural adaptation to the Portuguese language. The study was approved by the Ethics and Research Committee of Federal University of the State of Rio de Janeiro –UNIRIO (no 0036.000-09) and all patients signed the informed consent form.
Instrument
The DYMUS is a self-reported questionnaire composed by 10 questions that evaluate two dimensions: dysphagia for solids (positive scores in questions 1, 3, 4, 5, 7, 8 or 10) and dysphagia for liquids (positive scores in questions 2, 6 or 9). All the answers are dichotomous, coded as 1 or 0, depending on the presence or the absence of the event. The total score is achieved by the sum of the two dimensions, ranging from 0 to 10 points. Dysphagia is identified by at least one abnormal response and is considered alarming when the score is equal to or higher than three (Bergamaschi et al. 2008
2009).
At the time of the examination all the patients were asked whether they had swallowing problems and after that, irrespective of their response, the DYMUS questionnaire was administered by a trained speech pathologist.
The Expanded Disability Status Scale (FS/EDSS) (Kurtzke 1983) was used as a standardized neurological examination. The EDSS assesses neurological impairment and disability and was performed by a trained doctor. EDSS score varies between 0 and 10, a high score indicates a more severe disability (Sonder et al. 2012; Kurtzke 1983).
Translation, back-translation and cross-cultural adaptation of questionnaire
The translation, including forward and backward translations, and the cross-cultural adaptation of the DYMUS questionnaire were carried out according to international standards. The criteria proposed by Guillemin et al. (1993) and Beaton et al. (1976) we used, fulfilling the 5 steps for translation and cultural adaptation. The original version of the DYMUS questionnaire was translated to Portuguese by two Brazilian translators who were fluent in English, one being a health professional (speech and language therapist) and the other with no technical/scientific knowledge of the topic under study. The two translations were compared by the researcher in charge and the required adjustments were subsequently made with the consent of both translators resulting into a single version of the translation. This version was back translated into English by two bilingual translators, whose mother tongue is English, who had no access to the original English version of the questionnaire, thus preserving its ambiguity. The backward translation was compared and considered equivalent to the original version.
In the second phase of the study, comprehensibility and content validity of the questionnaire were tested using cognitive interviews with 40 MS patients (pilot study). In order to improve the intelligibility of the instruments when necessary and optimize the face and content validity for the main study, each patient was asked to explain what had understood about each question.
A committee composed by four health professionals with experience in neurology and dysphagia (one speech therapist, two neurologists and one physical education), bilingual, revised the produced versions in light of the difficulties presented by patients, making the semantic and idiomatic modifications as necessary. Questions 1, 2, 5, 8 and 10 were comprised of 100% of patients. Based on the information obtained, adjustments had to be made to questions 3, 4, 6, 7 and 9, besides substituting the words “deglute and deglutition” for “swallow”, given that those words were not understood by the patients. Furthermore, one patient had difficulty understanding the question 3 (2.5%), two (5.0%) in question 4 and 6, three (7.5%) on question 9 and 11 in question 7 (27.5%).
The definitive Brazilian version, named DYMUS-BR, was produced after the face and content validity results in the pilot study had been approved by this committee. The final version of the questionnaire was maintained with 10 questions, similar to the original version (Additional file 1).
Reliability and construct validity
To evaluate the reliability of the DYMUS-BR questionnaire we computed Cronbach alpha (Cronbach 1951), which is a reliability coefficient based on internal consistency. The internal consistency was estimated by Cronbach’s alpha coefficient for dysphagia as a whole and for dysphagia for solid and liquid. The Cronbach’s alpha coefficient was analyzed according to the Instrument Review Criteria (SAC): between 0 to 0.6 unsatisfactory reliability, between 0.6 to 0.7 satisfactory reliability, and between 0.7 to 1.0 high reliability (Scientific Advisory Committee of the Medical Outcomes Trust – SAC Instrument Review Criteria 1995). A questionnaire can be considered reliable if obtains values between 0.65 and 1 (Scientific Advisory Committee of the Medical Outcomes Trust – SAC Instrument Review Criteria 1995). In order to evaluate item homogeneity we computed the inter-item correlation matrix. Construct validity was evaluated by testing the operationalization of the measure dysphagia of the questionnaire against the patients’ self-assessment of dysphagia, used as a proxy, measured by the response to the initial question “Do you have difficulty swallowing?”. To achieve this, a cross-sectional study was performed. As recommended by (Dawson & Trapp 2004) the minimum number of patients to be tested should correspond to 10 patients for each item of the questionnaire to be validated. As DYMUS questionnaire has ten items, the inclusion of 100 patients was sufficient. Mann–Whitney U test was used to determine if differences existed and Spearman’s rank correlation coefficient (rs) was used to assess the significance of the association between DYMUS and patient’s self-assessment.
Data analysis
The descriptive analysis was conducted for characterization of the socio-demographic and clinical data of the patients. Categorical variables were shown as percentages. Continuous variables were shown as average or mean along with the respective standard deviation or percentile. The answers to the DYMUS-BR questionnaire were grouped into: without dysphagia (zero score) and dysphagia (1 or more abnormal response). Patients with dysphagia were classified as: dysphagia for solids (positive scores on questions 1, 3, 4, 5, 7, 8 or 10) or: dysphagia for liquids (positive scores on questions 2, 6 or 9). Moreover, dysphagia was classified as mild (1 or 2 abnormal responses) or alarming (3 or more abnormal responses) (Bergamaschi et al. 2008
2009). Cronbach’s alpha coefficient, inter-item correlation matrix, Mann–Whitney U test and Spearman’s rank correlation coefficient were used. A significance level of 0.05 was set. Data analyses were performed using Statistical Package for Social Sciences (SPSS), version 14.0, 2006 for windows software.