Dissociation between cutaneous silent period and laser evoked potentials in assessing neuropathic pain

In this study we investigate whether the cutaneous silent period (CSP)-an inhibitory response evoked in hand muscles by painful digital nerve stimulation-is useful for assessing nociceptive pathway function in patients with neuropathic pain. In 40 patients with peripheral neuropathy (21 without and 19 with neuropathic pain) we recorded the CSP in the abductor digiti minimi after fifth digit stimulation and also recorded laser evoked potentials (LEPs) after stimulation applied to the ulnar territory of the hand. Although the LEP amplitude was significantly lower in patients with pain than in those without (P < 0.005), the CSP duration did not differ between groups (P > 0.50). Pain intensity correlated significantly with LEP amplitudes (P < 0.005) but not with CSP duration (P > 0.5). Our findings indicate that the CSP is not useful for assessing nociceptive pathway function in patients with neuropathic pain.