Systemic adenosine infusion alleviates spontaneous and stimulus evoked pain in patients with peripheral neuropathic pain

In seven patients with peripheral neuropathic pain, the effect of systemic adenosine infusion on pain symptoms was evaluated in a double-blind, placebo controlled, cross-over study. The study infusions, adenosine (50 micrograms.kg-1.min-1) or placebo, were given intravenously (IV) during 45-60 min at two separate occasions. Before and during infusions, bedside examination of sensibility and quantitative sensory testing (QST), i.e., assessments of perception thresholds for touch, touch-evoked pain, cold, warmth, painful heat, and cold, were performed. In the neuropathic area, sensation magnitude was rated by a visual analog scale (100 mm VAS) using a pin and at perception threshold for touch-evoked pain using von Frey filaments. Adenosine infusion reduced spontaneous pain (P0.05), and caused an increase of the touch-evoked pain threshold from 10.8 +/- 5.3 to 22.2 +/- 6.9 g (P0.05), whereas placebo had no effect. Pain intensity at perception threshold for touch-evoked pain was, however, unaltered. Pinprick-evoked pain in the neuropathic areas was reduced from 53 +/- 11 to 29 +/- 10 mm (P0.05). No other sensory modality was consistently changed during adenosine infusion. In conclusion, the present study demonstrates that adenosine infusion alleviates spontaneous neuropathic pain, tactile allodynia, and pinprick hyperalgesia in patients with peripheral neuropathic disorders, probably by a central mechanism of action.