Direct and Indirect Pathways for Health-Related Quality of Life Change from Pain Improvement in Neuropathic Pain Patients with Spine Diseases: Path Analysis with Structural Equation Modeling Using Non-Interventional Study Results of Pregabalin

BACKGROUND: Chronic low back pain or chronic cervical pain often has a neuropathic pain (NeP) component and patients with these conditions complain of sleep deprivation, loss of physical function, and reduced productivity due to pain. The objective of this study was to clarify the pathway by which pain, sleep disturbance due to pain, and physical function status influence QOL measures in chronic low back pain patients with NeP associated with lumbar spine diseases (CLBP-NeP) and in chronic cervical pain patients with NeP associated with cervical spine diseases (CCP-NeP). METHODS: A model assuming pain numeric rating scale (NRS), pain-related sleep interference scale (PRSIS), and functional indices (Roland Morris Disability Questionnaire [RMDQ], Neck Disability index [NDI]) as factors that can affect outcomes such as QOL (calculated using EuroQoL 5 Dimensions (EQ-5D)), the Patient Global Impression of Change (PGIC), and the Clinical Global Impression of Change (CGIC) was developed using structural equation modeling. RESULTS: Overall trends were frequently observed in both patients with CLBP-NeP and CCP-NeP. Pain NRS had the largest comprehensive direct impact on QOL based on EQ-5D and an overall impression of changing symptoms. The effects of pain NRS on each outcome were largely due to direct pain-related effects; however, for EQ-5D, an indirect effect via functional improvement was the primary factor. CONCLUSION: Although the results of this study suggest that the indirect functional improvement of pain relief may not be recognized as a significant component of therapeutic effects by both physicians and patients, the pain-relieving intervention contributes directly to improvement of patients’ overall QOL and also indirectly via functional improvement in Japanese primary care settings. Accordingly, to achieve the therapeutic goal for patients with NeP and minimize the impact of pain burden, our findings indicate that pain relief interventions are also crucial from the perspective of the patient’s HRQOL.