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 ), the factor analysis revealed that a couple of individual items affected rather low alpha scores for the specific domains (Table ). 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 ).
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 ). 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.