Pronociceptive pain modulation in patients with painful chemotherapy-induced polyneuropathy

Context: Several chemotherapy agents induce polyneuropathy that is painful for some patients, but not for others. We assumed that these differences might be attributable to varying patterns of pain modulation. Objectives: The aim of the present study was to evaluate pain modulation in such patients. Methods: Twenty-seven patients with chemotherapy-induced polyneuropathy were tested for detection thresholds (cold, warm, and mechanical) in both the forearm and foot, as well as for heat pain threshold, mechanical temporal summation (TS), and conditioned pain modulation (CPM; also known as the diffuse noxious inhibitory control-like effect), which were tested in the upper limbs. Results: Positive correlations were found between clinical pain levels and both TS (r = 0.52, P = 0.005) and CPM (r = 0.40, P = 0.050) for all patients. In addition, higher TS was associated with less efficient CPM (r = 0.56, P = 0.004). The group of patients with painful polyneuropathy (n = 12) showed a significantly higher warm detection threshold in the foot (P = 0.03), higher TS (P < 0.01), and less efficient CPM (P = 0.03) in comparison to the group with nonpainful polyneuropathy. Conclusion: The painfulness of polyneuropathy is associated with a "pronociceptive" modulation pattern, which may be primary to the development of pain. The higher warm sensory thresholds in the painful polyneuropathy group suggest that the severity of polyneuropathy may be another factor in determining its painfulness.