Temporal relationships between changes in phantom limb pain intensity and changes in surface electromyogram of the residual limb.

Previous studies of relationships between surface EMG of the residual limb and phantom pain have not shown which changed first. Thus, predictive relationships could not be demonstrated. 24 male (20) and female (4) amputees between the ages of 33 and 71 who reported either burning (3), cramping (8), shocking-shooting-stabbing (6), or a combination of these descriptions of phantom pain (7) participated in one or two recording sessions. Raw surface EMG from the major muscles of the residual limb was recorded while subjects activated an event marker to indicate changes in pain. All eight subjects with cramping phantom pain reported changes in pain after the recording showed sharply demarcated increases in EMG. Subjects reporting either shocking-shooting or burning pain did not show any consistent relationships between EMG and pain. Three of the four subjects reporting experiencing both shocking-shooting and cramping phantom pain simultaneously during recordings showed changes in EMG preceding changes in pain. Sensations of cramping phantom pain were preceded by increases in muscle tension in the residual limb in almost every instance for each of our subjects showing changes in cramping phantom pain. Thus, changes in muscle tension in the residual limb are likely to either be causes or close intermediaries for the cause of cramping phantom pain but not necessarily of other common descriptors.