DREZ Myelotomy for Pain Control
Dorsal Root Entry Zone (DREZ) myelotomy (also known as DREZ procedure) refers to a surgical operation that selectively destroys the posterolateral aspect of the spinal cord, corresponding to the area through which dorsal (sensory) root fibers enter the cord itself.
Initially described by Marc Sindou of Lyon, the procedure was aimed at undercutting the lateral part of the dorsal roots and cutting into the matter of spinal cord as a means of treatment of chronic pain and spasticity (1). Called microsurgical DREZotomy, the procedure gained its popularity after Blaine Nashold of Duke University described modification of Sindou approach with deeper destruction of the spinal cord and recommended using it specifically in situations where dorsal roots have been avulsed (such as in traumatic brachial plexus avulsion) (2). Popularization of DREZ myelotomy by Nashold resulted in it being sometimes called “Nashold procedure” at least in the North American neurosurgical circles (3)
DREZ myelotomy is indicated for control of medically refractory chronic severe pain syndromes, primarily those associated with traumatic plexus avulsions (brachial or lumbar) (4). It has also been tried, with various degree of success, for other pain syndromes that at least partially arise from malfunction at the spinal cord level, such as “end-zone” pain after spinal cord injury (5), pain due to syringomyelia (6), or post-herpetic neuralgia (7). Best surgical candidates would have all of the following criteria: the pain is (A) chronic, (B) severe, (C) associated with known pathological substrate (such as brachial plexus avulsion documented by neurophysiological testing, MRI and/or CT myelography), (D) not-responsive to standard medical pain management approaches. There is no clear indication on whether patients considered for DREZ should exhibit failure of non-destructive surgical interventions (neuromodulation surgery – neurostimulation or intrathecal drug delivery).
The presumed rationale for DREZ myelotomy is deafferentation-related spontaneous hyperactivity of spinal cord neurons located in the most superficial Rexed layers (substantia gelatinosa, Lissauer’s tract and Rexed layer V) that are involved in processing of nociceptive information. Such hyperactivity develops in absence of the constant sensory input from periphery (due to mechanical disconnection of sensory pathways in cases of avulsion of the dorsal (sensory) roots) – known as deafferentation phenomenon – and results in severe neuropathic pain. By destroying the area of presumed abnormal hyperactivity, DREZ myelotomy permanently eliminates the deafferentation pain and improves the patients’ comfort and functionality.
Recommended approach for DREZ myelotomy includes laminectomy or hemilaminectomy at the level of planned intervention with dural exposure sufficient to get appropriate angle for the dorsal horn destruction. The DREZ is identified either by direct visualization of the dorsal roots or, in case of the root absence as happens in plexus avulsion, by drawing an imaginary line between normal roots above and below the avulsion level. Multiple ways to accomplish DREZ lesioning have been used and described in the literature. Four most commonly employed techniques use (A) the combination of mechanical cutting with surgical blade and subsequent enlargement / deepening of the lesion with bipolar coagulating forceps under direct vision (1); (B) a series of overlapping radiofrequency lesions made with a specially designed DREZ electrode that has a small area of insulation next to the active coagulation electrode with built-in thermocouple (2-8); (C) laser aimed at the DREZ, with both CO2 and argon laser devices (9); and (D) focused ultrasound delivered through a knife-like handle (10).
In each case, however, the goal of DREZ myelotomy remains the same – to selectively destroy Rexed laminae I through V and the Lissauer’s tract while preserving the adjacent posterior and lateral funiculi.
Results of surgery, in terms of pain relief and incidence of complications, vary significantly from series to series and from one indication to another. Commonly quoted series from Duke University and Queen Square Hospital stated about 60% pain relief in patients with brachial plexus avulsion treated with DREZ procedure based on series of 56 and 34 patients, respectively (4,8). Similarly good results were reported in patients with lumbar plexus avulsions and pain after spinal cord injury, whereas other indications, such as post-herpetic neuralgia and complex regional patients were significantly less responsive to this type of intervention with good and lasting improvement noted in 20-25% of patients (11). Complications in most series included changes in sensation observed in the lower part of the body, clumsiness and fatigue, sometimes affecting ambulation, in up to 40% of operated patients (4).
DREZ myelotomy is an established procedure for definitive resolution of intractable pain associated with certain neuropathic pain syndromes. When used in appropriately selected patients, particularly in those with post-traumatic avulsion of brachial or lumbar plexus or pain due to spinal cord injury, DREZ procedure may produce lasting and clinically meaningful pain relief in majority of patients while maintaining low incidence of side effects and complications.
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