Diffuse noxious inhibitory controls in humans: a neurophysiological investigation of a patient with a form of Brown-Séquard syndrome.

In normal subjects, the application of heterotopic painful stimuli induces simultaneous and parallel decrease in the sensation of pain and of the spinal nociceptive flexion (RIII) reflex evoked by electrical stimulation of the sural nerve. This inhibition of the RIII reflex is absent in tetraplegic patient with clinically complete spinal cord transections and can be triggered only from the analgesic hand in patients with Wallenberg's syndrome. These findings suggest that the inhibitory phenomena observed in normal subjects are likely to be examples of diffuse noxious inhibitory controls (DNICs), being sustained by a loop involving supraspinal structures, the ascending part of which is localized in the spinoreticular tract. We now report an exceptional case of a patient with Brown-Séquard syndrome due to a 4-year-old spinal cord lesion (left side, T-6 level) produced by a knife-wound in the back. Nociceptive flexion (RIII) reflexes elicited by stimulation of cutaneous afferents in the ulnar and sural nerves were studied in the upper and lower limbs by recording from the biceps brachialis and biceps femoris muscles, respectively. For each limb, the RIII reflex threshold was determined. The reflex was then elicited regularly by stimuli of 1.2 times threshold before, during, and after periods of nociceptive electrical conditioning stimulation (15 mA; 4 Hz; 1 min) applied successively to the other three limbs.(ABSTRACT TRUNCATED AT 250 WORDS)