The Brief Pain Inventory: Pain's interference with functions is different in cancer pain compared with noncancer chronic pain

Objectives: The Brief Pain Inventory (BPI) is a highly recommended and frequently used multidimensional pain assessment tool. The BPI includes 2 dimensions: pain intensity and pain's interference with functions. Our aims were to explore how patients respond to pain interference items by comparing responses from patients who had cancer with patients who had noncancer chronic pain (NCCP), and to explore how different levels of health-related quality of life affect upon pain's interference with functions. Methods: Three hundred patients with cancer and 286 patients with NCCP were asked to complete the BPI and the European Organization for Research and Treatment of Cancer's Quality of Life Questionnaire (EORTC QLQ-C30). The pain interference items were indexed into total interference, interference with physical functions, and interference with psychologic functions. Regression analyses were used to explore differences in pain's interference by group, pain intensity, and a possible interaction effect between them. The analyses were adjusted for age, sex, and all EORTC QLQ-C30 scales. Results: The cancer patients reported higher values of physical interference than NCCP patients with the same level of pain intensity (P < 0.001). NCCP patients reported higher values of psychologic interference than cancer patients (P = 0.023). For total interference, these effects eliminated each other. When adjusting for age, sex, and the EORTC QLQ-C30 subscales, the results still remained significant except that adjusting for the subscale for physical function made the group effect insignificant for physical interference (P = 0.30). Discussion: The results indicate that patients are unable to report isolated pain's interference using the BPI. When reporting pain's interference with physical functioning, the level of physical functioning is more important than the level of pain. Patients' diagnoses have to be taken into account when interpreting reported pain's interference with functions.