Pain-related disability measurement: the cultural adaptation and validation of " pain disability index (PDI)" and " pain disability questionnaire (PDQ)" among Iranian low back pain patients

Low Back Pain (LBP) is still a medical problem in 21 st century. Having back pain and being disabled by it are not the same thing. It is common to come across with patients who have simple back pain but surprisingly totally disabled and vice versa. In clinical practice, it is important to have a proper evaluation of disability and making a clear distinction between pain and disability. During the past two decades several selfreport measures and questionnaires have been developed to evaluate disability in LBP patients, however most of these questionnaire were designed in English language and based on European or American studies. The aim of this study was to develop and validate a translated and culturally adapt “Pain Disability Index (PDI)” and “Pain Disability Questionnaire (PDQ)” among Iranian patients with low back pain. The Persian versions of the PDI, PDQ were created through systematic translation and crosscultural adaptation of the original questionnaires. The Oswestry Disability Index and Visual Analogue Scale were used for validation studies. Patients were asked to complete these questionnaires initially and also at 7 days later as retest. A total of 304 patients with acute and chronic LBP completed the Persian versions of PDI, PDQ, “Oswestry Disability Index” (ODI) and “Visual Analogue Scale” (VAS). Among patients 111 patients participated for retest after seven days. The Cronbach’s alpha (coefficient of reliability) for the PDI and PDQ was satisfactory. The PDI and PDQ showed high and very high test-retest reliability (ICC=0.8 and 0.92 respectively). The Pearson correlation coefficient among PDI, PDQ with ODI was 0.64 and 0.72, and for PDI, PDQ, ODI with VAS was 0.36, 0.47 and 0.57, respectively (P<0.001). The Persian version of the PDI and PDQ questionnaires are reliable and valid instruments to evaluate generic perceived disability in Persian-speaking patients with LBP. It is shown that PDI and PDQ are capable of measuring the disability in LBP patients. They could be used in clinical and research encounters with acceptable confidence.