Duloxetine in patients with central neuropathic pain caused by spinal cord injury or stroke: a randomized, double-blind, placebo-controlled trial

The mechanisms underlying central neuropathic pain are poorly understood. Pain inhibitory mechanisms including sertononergic and norepinephrine systems may be dysfunctional. In this randomized, double-blinded, placebo-controlled trial we evaluated the effects of duloxetine on pain relief (spontaneous pain and evoked pain), tolerability, health status, and quality of life in patients with central pain related to cerebrovascular lesions or spinal cord lesions. At baseline and eight weeks following start of treatment subjects were evaluated with standard measures of efficacy: pain intensity (primary efficacy variable), quantitative sensory testing, health status and quality of life (secondary efficacy variables). Forty-eight patients received escalating doses of either duloxetine (60 and 120 mg/day) or matching placebo capsules. In both groups, patients started with 1 capsule per day. If pain relief was insufficient, patients were titrated to a higher dose. A trend towards a decrease in mean pain score after eight weeks was observed for duloxetine treatment (p = 0.056). Duloxetine alleviated dynamic (p = 0.035) and cold allodynia (p < 0.001) significantly better than placebo. Tactile pain and pressure pain thresholds did not improve significantly. The duloxetine group showed a significant improvement for the bodily pain domain of the SF36 (p = 0.035). No significant differences were observed in the other domains of the SF36, the Pain Disability Index, and the EQ-5D. While this trial showed no significant effect on pain intensity, duloxetine revealed a biologic effect. It would be worthwhile to suspend our judgement and to perform more studies to evaluate the role of duloxetine in modulation of the symptoms of central neuropathic pain.