Irritable bowel syndrome (IBS) is a common gastrointestinal disorder and is often associated with psychological distress 12. People with IBS have a significantly diminished quality of life (QOL) 34. Even though a large percentage of subjects with IBS do not seek medical care (approximately 75%) 5, IBS is associated with significantly more absences from work and school and with impaired QOL 34. The impact on QOL in patients with IBS is often underestimated by friends and family members, and even by the patient's doctors because they are not disabled in any obvious way and there is no apparent impact on life expectancy.

How much of a burden illness is on an individual's life depends on several factors. It is becoming recognized that assessment of QOL associated with a person's illness should be taken into account in order to understand the burden illness on several medical conditions. We have demonstrated that both IBS patients and IBS non-consulters report not only more severe gastrointestinal symptoms and psychological distress but also more impaired health-related QOL than people who do not have IBS, as has been reported in other countries 6. In contrast to reports form the United States 7, IBS patients were not different from IBS non-consulters for physical and psychological QOL scores on the SF-36 8.

Although generic instruments like the SF-36 offer the opportunity to compare the impacts of different conditions on health status 910, disease-specific measures are more sensitive than generic measures of QOL to the effects of illness and the impact of treatment 9. Within the gastroenterology field, disease-specific quality-of-life measures have been developed primarily for inflammatory bowel disease 11.

Patrick and Drossman developed and validated a specific QOL measure, the IBS-QOL, to assess the impairment of QOL in IBS 12. The instrument defines "perceived quality of life" according to a needs-based model that considers QOL as the degree to which all or most needs are met 13. It reveals patients' predominant concerns with high degree of specificity and attribution to the bowel symptoms associated with the condition 12. Furthermore, they confirmed that this instrument is responsive to treatment in a clinical population of patients with FBD 14. This instrument has been translated into several languages (i.e. Dutch, Spanish, French, Chinese and Korean) and is widely used 15161718192021.

There have been no studies on the cross-cultural differences in IBS between the U.S. and Japan due to the lack of common disease-related instruments. To compare QOL in patients with IBS between these countries, it is indispensable to develop disease-specific QOL measurements like the IBS-QOL in Japanese. The aim of this study was to test the reliability and validity of a Japanese version of the IBS-QOL (IBS-QOL-J).

Forty-nine consecutive patients (27 female and 22 male) who suffered with chronic or recurrent abdominal pain, abdominal discomfort and/or altered bowel habit in Tohoku University Hospital, Sendai, Japan were invited to participate. All the participants completed the IBS-QOL-J (see Additional file 1) concomitant with a Japanese version of the IBSSI (IBSSI-J) 22 twice between 7–14 days interval to confirm the test-retest reproducibility. The Japanese version of the Rome II modular questionnaire, in conjunction with medical evaluation to exclude alternative diagnosis, was used to diagnose IBS 22. None of the participants had any organic GI diseases or any other severe physical and/or psychological disorders. Age, sex, marital status, education, race, number of visits to physicians due to GI symptoms, and existence of continuous or nearly continuous abdominal pain in the past 6 months were also investigated (Table 1). This study was approved by the Tohoku University Ethics Committee (No. 2004-061). All the participants gave written informed consent.

The Rome II modular questionnaire (RMIIQ) has been used as a diagnostic instrument for functional GI disorders according to Rome II diagnostic criteria 23. This instrument includes 4 key questions used to define IBS plus 11 supportive items that address bowel habits. IBS is defined by abdominal discomfort or pain that was present during at least 3 weeks in the last 3 months and that has two of three features: (1) Relieved with defecation; and/or (2) onset associated with a change in frequency of stool; and/or (3) onset associated with a change in form (appearance) of stool 2223. Subtypes of IBS were assessed by predominant stool pattern; hard or lumpy stools >25% and loose (mushy) or watery stools <25% of bowel movements as IBS with constipation (IBS-C), and loose (mushy) or watery stools >25% and hard or lumpy stools <25% of bowel movements as IBS with diarrhea (IBS-D) 24.

The IBS Severity Index (IBSSI) was developed and validated in the U.K. to assess the major GI symptoms in IBS 25. This scoring system is simple and consists of only 5 items each with 100-point scale (0, none; 100, worst). These items are severity and duration of abdominal pain, severity of abdominal distension, dissatisfaction with bowel habits (bowel score) and interference with life in general (QOL). The maximum total score is 500 points 2225. Recently, these two instruments have been translated into Japanese and validated for Japanese patients with functional bowel disorders (FBD) by our research group 22.

The IBS-QOL consists of 34 items with 5-point response scales (0 to 4). The IBS-QOL is scored for 8 subscales; dysphoria (8 items), interference with activity (7 items), body image (4 items), health worry (3 items), food avoidance (3 items), social reaction (4 items), sexual concerns (2 items) and relationships (3 items) 12. Higher values indicate better QOL after converting the raw score on the IBS-QOL into 0 to 100 points. The process for the validation study of the IBS-QOL-J was as follows: The original 34 items of the IBS-QOL were translated from English into Japanese through two independent forward translations (by M.K. and S.F.), resolution, back translation by a native speaker of English, and resolution of differences. As a result of the discussion among the translators and the authors of the original version (D.A.D. and W.E.W.), no obvious difference of contents was found between the original and the back-translated versions.

Cronbach's alpha was calculated to assess the internal consistency reliability. A high internal consistency suggests that the scale is measuring a single construct. Reproducibility was assessed by comparing the total IBS-QOL-J score at baseline to a second one later. Convergent and discriminant validity involve comparing logically related measures to see if they are correlated more strongly (convergent) or more weakly (discriminant). The overall score for the IBSSI-J and the scores for the 5 components at baseline were used to assess convergent validity of the IBS-QOL-J. Strengths of association as the test-retest reliability or the convergent/construct validity were tested by a simple regression analysis, Pearson's correlation coefficient. Multiple regression analysis was used to confirm the relationships among the IBS-QOL-J score, age, gender, education and marital status.

Characteristics of the participants are shown in Table 1. The mean age with standard deviation (SD) of participants was 38 +- 15 years (19–79 years old). Thirty patients were diagnosed as IBS by the Japanese version of Rome II modular questionnaire, and the rest of them were considered to have other FBD. Six patients diagnosed as IBS were constipation predominant (IBS-C), 14 were diarrhea predominant (IBS-D) and 10 were not classifiable as either. Overall score of the IBS-QOL-J demonstrated high reproducibility (intraclass correlation coefficient, 0.92, p < 0.001) and high internal consistency (Cronbach's alpha, 0.96). Each individual score on the IBS-QOL-J also showed high reproducibility and relatively high internal consistency (Table 2). Response to the individual items significantly correlated with overall score of the IBS-QOL-J except for Q5 from the body image domain and Q32 from the health worry domain (Table 3).

Validity of the IBS-QOL-J was confirmed by the significant correlations with measures of disease severity. The overall score of IBS-QOL-J was significantly correlated with overall severity of IBS symptoms on the IBSSI-J (r = -0.36, p = 0.01) and with the individual questions on the IBSSI-J that assess interference with life in general (r = -0.47, p = 0.001) and dissatisfaction with bowel habits (r = -0.32, p = 0.03, Table 4). The correlations between the overall score of the IBS-QOL-J and individual scores of abdominal pain (severity and duration) were weaker and were not statistically significant. Abdominal distension (severity) on the IBSSI-J was correlated to quality of life was as measured by the IBS-QOL-J.

Linear regression analyses revealed that the number of physician visits in the past 6 months was significantly associated with the overall score of IBS-QOL-J (r = -0.33, p < 0.05) but not with the overall severity score (r = 0.19, p > 0.1). Eight patients who reported continuous or nearly continuous abdominal pain in the past 6 months had significantly lower scores in the IBS-QOL-J than those who did not (53.7 +- 12.7 vs. 73.6 +- 19.5, p < 0.01, Fig. 1). There was no significant difference in the overall score or each of individual score on the IBS-QOL-J between patients who were diagnosed as IBS by the RIIMQ and those who were not (namely, the other FBD) in the participants (Table 5). Age, sex, education or marital status did not affect scores on the measure as a predictor variable. Most of the IBS-QOL-J scores in Japanese patients with IBS were quite comparable to those in the English version of the IBS-QOL in IBS patients in the U.S. There was no significant difference in the overall or each individual score on the IBS-QOL-J between subtypes of bowel movement in 30 patients diagnosed as IBS.

The Japanese version of the IBS-QOL (IBS-QOL-J) instrument was confirmed to be reliable and valid. This disease-specific QOL measurement shows high internal consistency for the overall score. The reproducibility over the two-week study period was excellent. The original version of the IBS-QOL has previously been shown to have high internal consistency and reproducibility 12. On this original instrument, discriminant and convergent validity 12 and responsiveness 14 were also demonstrated. Not only severity of symptoms but also psychological well-being predicted this score 26. Although Cronbach's alpha scores for most of the individual domains also resulted high (Table 2), the factor analysis revealed that a couple of individual items affected rather low alpha scores for the specific domains (Table 3). Further larger studies should be needed to confirm whether cross-cultural differences in patients' concerns might be associated with the inconsistencies in the present study.

Disease-specific quality of life instruments are sensitive and responsive to measuring treatment response over time; thus, they are especially useful in clinical research trials in which health status is analyzed 9. Several disease-specific QOL measures for IBS or functional GI disorders have been developed (e.g. IBSQOL developed by Hahn et al. 27). However, in most instruments, their responsiveness has not been demonstrated except for the IBS-QOL. In a systematic review by Bijkerk et al, it was shown that the IBS-QOL is the best of the five IBS-specific QOL scores to establish changes in health-related QOL 28. On the other hands, the IBS severity index (IBSSI) is considered to be the best choice for a detailed IBS symptom assessment 28.

Recently, we have translated the Rome II modular questionnaire for IBS and the IBSSI into Japanese and have confirmed reliability and reproducibility in patients with functional bowel disorders (FBD) 22. Our results in the present study show that the IBS-QOL-J is strongly correlated with the self-rating scales for the overall severity measure. Besides, patients who reported continuous or nearly continuous abdominal pain showed a lower overall score on the IBS-QOL-J than those who did not. On the other hand, our study did not confirm that there are significant differences in the QOL score among subtypes of bowel movement in patients with IBS. These results suggest that IBS patients who have abdominal pain continuously may have more impaired QOL despite predominant stool patterns. Furthermore, patients considered as frequent consulters according to a previous systemic review 29 show lower scores in the IBS-QOL-J. Previous reports on the original IBS-QOL show a significant association between the IBS-QOL and number of visit to physicians for IBS problems 14. Thus, the findings of the present study are consistent with those of the original version of the disease-specific QOL measure for IBS.

The mean overall score of the IBS-QOL-J in patients with IBS was similar with that of original version 12 measured in the U.S. (68.2 vs. 63.2 points) despite different diagnostic criteria (Rome II vs. Rome I) and subject population (tertiary care vs. GI clinic plus advertisement). The mean overall score of the IBS-QOL-J in patients with IBS also showed a similar result with that measured by the Korean version of the IBS-QOL in South Korea 21. Nevertheless, the mean individual scores of body image (80.0 vs. 62.5), health worry (73.1 vs. 59.2), food avoidance (55.3 vs. 43.4) and sexual concerns (89.2 vs. 73.5) on the Japanese version were over 10-point higher 12 (see Table 5).

Our results failed to confirm that the overall IBS-QOL-J score is significantly associated with the individual scores of the abdominal pain severity or pain duration in the IBSSI-J. We do not believe that gastrointestinal (GI) symptoms of the patients in this study were less severe because more than two-thirds demonstrated moderate to severe symptoms on the IBSSI-J according to the severity classification system on the original version 25 (see Table 1). Despite 41 of 49 patients had taken medical treatment for their GI symptoms including antispasmodic agents and antidepressants, they did not report lower abdominal pain scores compared with the rest of the patients who had not in the present study.

It has been demonstrated that the Japanese subjects are less prone to be accepting of pain behaviors 30 and express their sexual activities to someone 31 compared with people in the Western countries. There was no difference in the individual score of sexual concerns between married and unmarried patients in this study, in fact. When the sexual concerns are assessed in the Japanese patients, it should be taken into account that they may hesitate or avoid expression of such topics even if they have any sexual problems. Although we could not compare differences in these scores directly, cross-cultural difference between the countries (e.g. race, food, belief, social milieu and health-care system) might affect some dimensions of perception for the health-related QOL in patients with IBS.

The IBS-QOL-J appears to be a reliable instrument to assess the disease-specific QOL for IBS in Japanese patients. However, this validation study was cross-sectional, and thus could not investigate responsiveness. Moreover, our sample was relatively small and recruited from only the referred FBD patients. Further validation studies are warranted to investigate reliability and validity on the Japanese version of the IBS-QOL. It is important to assess not only severity of symptoms but also disease-specific QOL when considering the strategy for treatment for IBS since no biological measure is available for assessing IBS. Considering cross-cultural comparisons, these instruments are likely to be a valuable tool to investigate the QOL in Japanese patients with IBS.