Identification of cut-points for mild, moderate and severe pain due to diabetic peripheral neuropathy

This study identified discrete categories of pain severity in a sample of patients with painful diabetic peripheral neuropathy (DPN), through derivation of cut-points on a 0-10 scale of pain severity (Brief Pain Inventory-DPN, BPI-DPN). Subjects were participants in a burden of illness survey (N=255). Serlin and colleagues' method establishing cut-points for cancer pain was adapted, considering all possible cut-points between 4 and 8. Optimal cut-points were those that created three pain severity categories producing maximum between-category differences on the seven BPI-DPN Interference items, using MANOVA. Cut-points of 4 and 7 optimally classified the sample for both Worst Pain and Average Pain, creating categories of mild, 0-3; moderate, 4-6; severe, 7 and higher (Hotelling's T(2)=22.95 and 16.20 for Worst and Average Pain, P<0.0001). Mean BPI-DPN Interference was 2.1 (SD=2.1), 4.9 (SD=1.9) and 7.4 (SD=1.6) for the mild, moderate and severe pain categories. Patients in the three categories differed significantly on patient-rated outcomes (Medical Outcomes Study Short Form-12v2 Mental and Physical Component Summaries and EuroQOL utility score), and on DPN-related healthcare visits (P<0.001). The labels 'mild, moderate and severe' Worst and Average Pain corresponded with patients' ratings of their pain using a verbal rating scale. This research shows that three categories of DPN pain severity can be identified based on interference with daily function, and that these categories are associated with patient outcomes and medical utilization.