Surgery in the DREZ for Refractory Neuropathic Pain After Spinal Cord/Cauda Equina Injury

Abstract

Chronic pain after spinal cord/cauda equina injury is reported at 10% to 35% of the injured patients according to literature data quoted in review articles (13, 16). Pain may be of course related to persisting compressive factors in relation with bony instability, deformity, or bone fragments within the canal; if present they should be treated surgically. Pain may also correspond to neuropathic pain in the affected spinal cord/ spinal root segments, and/or in the territory caudal to the level of the lesion. In patients whose pain has a “radiculo-metameric” distribution, that is, the pain corresponding with the level and extent of the spinal cord and the spinal root lesions (we call this pain, segmental), surgery in the DREZ gives satisfactory effects (1, 2, 9, 11, 12, 16-18, 20). In contrast, pain in the territory below the lesion, especially in the perineal-sacral area, is not influenced even if DREZ lesioning is performed at the (lower) corresponding medullary segments. This is particularly true when the pain consists of a permanent burning sensation and is located in an infralesional, totally anesthetic, area. Segmental pain is known to be related to the crush of the underlying medullary segments, and/or nerve root contusion, entrapment, or scaring at the level of injury. These lesions generate deafferentation of, or direct damage to, the corresponding central neurons. Deafferented dorsal horn neurons acquire abnormal spontaneous patterns of discharge that can be recorded with microelectrodes during surgical procedures (3, 5-7). On these bases DREZ surgery must be reserved for segmental pain. Lesioning should be targeted not only to the injured medullary segments but also to the adjacent ones if modified by consecutive pathologic process (eg, atrophy, cavitation, gliosis, arachnoiditis). Lesioning should involve the corresponding radicular levels when nerve roots are markedly altered. In patients with incomplete paraplegia, it is of paramount importance that DREZ lesioning be performed not too deeply and not too extensively, to avoid additional neurological deficits. On the contrary, in patients with complete motor and sensory deficits, DREZ surgery can be done widely on the selected segments. Best indications are traumatic lesions in the thoracolumbar vertebral junction with complete functional interruption of the conus medullaris, especially when the pain is located in the legs ( segmental pain) rather than in the perineum ( infralesional pain). Pain caused by lesions in cauda equina can also be favorably influenced by DREZ surgery performed at the corresponding spinal cord metameric segments. In a previously published study (16) 27 of our 37 patients (73%), with segmental pain distribution, of 8 to 10 of intensity on the visual analogic scale, had good long-term pain relief, that is, they did not need any narcotics or permanent analgesic medications. Among these 37 patients, 22 of the 25 who had paroxystic electric shock attacks as the main component of their pain (88%) had good relief. Conversely in the group of the 12 patients with permanent burning pain as the dominant component, only 5 (42%) had good relief. These results are concordant with the ones from the reviewed article; only 20% of their patients affected with what they named thermal pain had good response to the DREZ procedure. Because paroxymal pain is better influenced by DREZ surgery is in agreement with the hypothesis of its dorsal horn (DH) origin, likely deafferentation hyperactivity of the DH body cells (3-7). We also hypothesize that the continuous component, especially when of the burning type, which is not so well influenced, could be at least in part the clinical expression of impairment or even the destruction of the DH body cells and of the subsequent