Association between the systemic immune-inflammation index and severe sleep disturbance in patients with neuropathic pain: a prospective longitudinal observational cohort study

Patients with neuropathic pain frequently experience clinically important sleep disturbance, but accessible biomarkers associated with sleep impairment remain limited. In this prospective longitudinal observational cohort study, 135 patients aged 40–65 years with DN4-confirmed neuropathic pain were assessed at baseline and 1 month after pulsed radiofrequency (PRF). Severe sleep disturbance was prespecified as a Pittsburgh Sleep Quality Index (PSQI) score > 10. Baseline systemic immune-inflammation index (SII), calculated from platelet, neutrophil, and lymphocyte counts, and first-morning urinary melatonin were compared between patients with and without severe sleep disturbance. At baseline, 73 patients met the severe sleep-disturbance criterion and 62 did not. Baseline SII was higher and urinary melatonin was lower in the severe sleep-disturbance group (both P < 0.01). SII correlated positively with PSQI score ( r = 0.575, P < 0.001) and remained associated with severe sleep disturbance after adjustment for sex and body mass index (adjusted OR per unit increase, 1.011; 95% CI, 1.007–1.014, P < 0.001). Exploratory receiver operating characteristic analysis yielded an area under the curve of 0.833 (95% CI, 0.764–0.903). At 1 month, fewer patients met the severe sleep-disturbance criterion, SII and PSQI scores were lower, and urinary melatonin was higher than at baseline. Because there was no untreated or sham comparator, these longitudinal changes cannot be attributed specifically to PRF. Higher SII was associated with more severe sleep disturbance in this heterogeneous neuropathic-pain cohort. These findings support SII as a candidate biomarker for identifying patients at increased risk of severe sleep disturbance, although external validation and mechanistic studies are required before clinical application.