Effects of regional anesthesia on phantom limb pain are mirrored in changes in cortical reorganization

Abstract

The causes underlying phantom limb pain are still unknown. Recent studies on the consequences of nervous system damage in animals and humans reported substantial reorganization of primary somatosensory cortex subsequent to amputation, and one study showed that cortical reorganization is positively correlated with phantom limb pain. This paper examined the hypothesis of a functional relationship between cortical reorganization and phantom limb pain. Neuroelectric source imaging was used to determine changes in cortical reorganization in somatosensory cortex after anesthesia of an amputation stump produced by brachial plexus blockade in six phantom limb pain patients and four pain-free amputees. Three of six phantom limb subjects experienced a virtual elimination of current phantom pain attributable to anesthesia (mean change: 3.8 on an 11-point scale; Z = -1.83; p < 0.05) that was mirrored by a very rapid elimination of cortical reorganization in somatosensory cortex (change = 19.8 mm; t(2) = 5.60; p < 0.05). Cortical reorganization remained unchanged (mean change = 1.6 mm) in three phantom limb pain amputees whose pain was not reduced by brachial plexus blockade and in the phantom pain-free amputation controls. These findings suggest that cortical reorganization and phantom limb pain might have a causal relationship. Methods designed to alter cortical reorganization should be examined for their efficacy in the treatment of phantom limb pain.

Fig. 1.

Coronal section through the postcentral gyrus (somatosensory cortex) of one phantom limb pain subject showing the pre-brachial–plexus-blockade shift of the cortical lip representation into the amputation zone (smaller polar angle 46°, left side of figure) compared with the location of representation of the lip on the intact side (larger polar angle 64°, right side of figure). On the right side of the figure, the green line from the origin intersects the representation of the intact-side lip on the surface of the cortex; the line forms an angle of 64° with the z axis through Cz. The green line on the left intersects the representation of the amputation-side lip on the surface of the cortex; it makes a smaller angle with the z axis through Cz (46°), indicating that the representation of the lip on the amputation side had shifted into (invaded) the amputation zone, which had represented the now absent hand. Eighteen degrees (64 − 46°) represents ∼36 mm of cortical reorganization along the curved surface of the cortex (i.e., ∼2 mm/degree).

Fig. 2.

Cortical representation of the digits and the lower lip before and after brachial plexus blockade in a unilateral upper extremity amputee with phantom limb pain who experienced complete pain relief attributable to the regional anesthesia. The location of the representation of the fifth digit (D5) of the intact hand before anesthesia is indicated by the red filled square, and the locations of the representations of the lip of the intact side and of the amputated side by the green filled squares (pre anesth. lip). The mirror images of the intact digit and the intact lip projected onto the amputation-side hemisphere are marked by open squares of the same colors. These locations refer to the period before anesthesia. The location of the representation of the amputation-side lip after anesthesia (post anesth. lip) is indicated by the yellow filled square. The central sulci on both sides are marked in blue. Note that before brachial plexus blockade, the lip on the amputated side (green square) had shifted into the region occupied by the representation of the fingers on the intact side (mirror D5). Twenty minutes after amputation stump anesthesia, the phantom pain was almost eliminated; at the same time there was a dramatic shift of the amputation-side lip back toward the position occupied by the lip representation on the intact side (mirror lip, open green square). The white dots are the vitamin E capsules marking the electrode positions.

Fig. 3.

Cortical representation of the digits and the lower lip before and after brachial plexus blockade in the three amputees with reduction of phantom limb pain (pr1, pr2, pr3; left) and the three amputees without phantom limb pain reduction (npr1, npr2, npr3; right). The central sulci on both sides are marked in blue. Note the shift of the lip representation back into a more lateral and frontal position in the upper limb amputees with phantom limb pain reduction attributable to anesthesia as compared with the relative lack of change in the amputees without pain reduction during anesthesia.