Original article

Dorsal root entry zone coagulation for Treatment of Deafferentation Pain Syndromes

ZHANG Xiao-hua, LI Yong-jie, HU Yong-sheng, TAO Wei and ZHENG Zhe

Keywords: deafferentation pain; DREZ coagulation; effectiveness

Background  Deafferentation pain is a kind of chronic pain syndrome and hard to manipulate. To study the effectiveness and safety of junctional dorsal root entry zone (DREZ) coagulation, 23 consecutive patients with intractable deafferentation pain syndromes were followed.

Methods  Twenty-three patients underwent junctional DREZ coagulation (C5-T1 for upper extremities and L2-S1 for lower extremities) under general anesthesia. The pain severity was evaluated by the short McGill pain questionnaire (MPQ) and the visual analog scale (VAS), and the depression and anxiety of patients were assessed by Hamilton Rating Scale for Depression (HRSD), Hamilton Anxiety Scale (HAMA), Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS).

Results  All patients experienced significant pain reduction immediately after surgery. The scales of short MPQ and VAS at pre-operation, 6-month and 12-month follow-up were 31.5±3.4 and 8.8±1.5, 6.5±1.9 and 2.5±2.2, 7.1±2.1 and 2.9±1.9, respectively. The postoperative scores comparing to pre-operative scores showed a statistically significant difference (P <0.01). The depression and anxiety state was also significantly relieved. At 12-month follow-up 6 patients had complete pain relief, 11 had excellent results with more than 75% pain relief, 17 had good results with more than 50% pain relief (73.9%). The main postoperative complications were transient slight hemiplegia (8), hypesthesia and paresthesia (15), a bearing down feeling of affected extremity (6), and deep sensory disability in the lower limbs (4) on the operated side. Because of the long time and prone position of the operation, 13 cases had a transient hyperalgesia in the upper chest.

Conclusion  DREZ coagulation is a safe and effective procedure in the treatment of deafferentation pain syndromes.

Chin Med J 2008;121():

D

eafferentation pain is a common chronic pain syndrome. Pain after brachial plexus root avulsion and phantom limb pain are likely to become intractable. After sustaining brachial plexus injury about 20% to 30% of patients experience long-term chronic pain in the upper limbs, and the incidence of phantom limb pain in traumatic amputated extremities is as high as 65% to 85%. Deafferentation pain can appear immediately after trauma, or months and years after trauma or amputation. Besides severe physical injury of the extremities, pain is also a main disability factor. Drug therapy and routine surgical operation cannot mitigate the pain effectively. Recently, an increasing number of researches have proven that deafferent pain is derived from the dorsal horn, mediated by second level neurons and that junctional DREZ coagulation can relieve the pain effectively. The aim of this study was to evaluate the effectiveness and safety of junctional DREZ microcoagulation, in deafferentation pain.

Beijing Institute of Functional Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing, 100053, China (Zhang XH, Li YJ, Hu YS, Tao W and Zheng Z)

Correspondence to: Prof. Li Yong-jie, Beijing Institute of Functional Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing, 100053, China (Tel: 86-10-83198899 ext 8484. Fax: 86-10-83163174. Email: functionsurg@sina.com)

METHODS

Materials

From November 2002 to December 2005 twenty-three patients with deafferentation pain syndrome underwent DREZ coagulation. There were 22 males and 1 female, aged 34 to 68 years (mean 52±8 years). The pain history extended from 12 months to 30 years. Pain appeared in all the cases after trauma, some cases immediately, and the longest interval between pain initiation and trauma was 16 years. Of the patients, 10 had phantom limb pain, 12 had pain after brachial plexus avulsion, 1 had stump pain; 21 had pain in the upper limb and 2 in the lower limb. The pain was described as persistent, electrical, burning, cutting, pulling or pressing, with unexpected aggravations. Nerve transplantation, such as intercostal, phrenic or accessory nerves (12 cases), neurofibroma resection (6) and transcranial magnetic stimulation (1) usually resulted in little pain reduction (12). MRI examination of cervical or lumbar cord indicated atrophy of cervical or lumbar enlargement, laterocrypt cyst formation and absence of a spinal space-occupying lesion.

Methods

All 23 patients underwent C5-T1 (upper limb) or L2-S1 (lower limb) junctional DREZ coagulation under general anesthesia (Figure). The operation was carried out in the prone position; a hemilaminectomy of the cervical or lumbar spine was performed and an incision of the dura and arachnoid maters was made. The exposed spinal cord usually revealed atrophy and adherence, as well as rotation or displacement when there was severe adherence, and absence of the dorsal roots/anterior roots in the C4-T2 segment and remnant foveola. Under a microscope, the dorsolateral sulcus of the spinal cord where the dorsal roots entered the spine were identified, and the pia mater was incised along the dorsolateral sulcus, and separated with the durodissector. A junctional coagulation was performed with a bipolar forceps at an angle of 45 degrees with the midline sagittal plane and to a depth of 3 mm, extending to the head of the poster horn. After operation, the patient lay in bed for 3 weeks, and then began to walk with neck support.1

Figure. A: Performed a junctional coagulation was with the bipolar forceps along the dorsolateral sulcus. B: DREZ in C5-T1.

Effectiveness assessment

The pain severity was evaluated by the short McGill pain questionnaire (MPQ) and the visual analog scale (VAS). The results were classified as complete pain relief (scale 0 point), excellent (more than 75% pain relief), good (more than 50% pain relief), fair (more than 25% pain relief) and bad (less than 50% pain relief). The depression and anxiety of the patients were assessed by Hamilton Rating Scale for Depression (HRSD), Hamilton Anxiety Scale (HAMA), Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS).

Follow-up

Follow-up data were obtained at the clinic or by telephone at 6 and 12 months after operation.

Statistical analysis

All data were expressed as the mean and standard deviation (Mean±SD) and analyzed by paired-sample t test. A P value less than 0.05 was considered statistically different.

RESULTS

Pain level evaluation

When completely wake from general anesthesia, all the patients felt significant pain relief, and 11 cases had obtained complete pain relief. At 6-month follow-up the short MPQ and VAS scores were all decreased significantly, i.e., in both the short MPQ and VAS scores decreased more than 50% in 19 cases (82.6%), the short MPQ and VAS scores decreased by more than 75% in 12 cases (52.2%) and 13 cases (56.5%), respectively; and 6 cases obtained completed pain relief (39.1%). In comparison with pre-operation pain scores, there was a significant difference (P <0.01). At 12-month follow-up MPQ and VAS scores rose slightly, but were clearly still less than pre-operation scores (P <0.01), i.e., 17 cases had more than a 50% decrease in short MPQ and VAS scores, short MPQ and VAS scores decreased by 75% in 11 cases and 12 cases, respectively; and 6 cases were still completely pain-free. Comparison between data obtained at 6- and 12-month follow-up revealed no difference (Table). At 24-month follow-up, 8 cases still maintained the good effect.

Amelioration of anxiety and depression

All patients were in a state of severe anxiety and depression. Scores of HAMA, HRSD, SAS and SDS before operation were 43.75, 64.8, 62.5 and 77.6, respectively. After DREZ coagulation these scores were significantly decreased (P<0.01), approaching the normal range, especially the anxiety scores; the scores did not change appreciably during the 12-month follow-up.

Table. Scores of pain, depression and anxiety (Mean±SD)

short-MPQ

VAS

HAMA

HRSD

SAS

SDS

pre-operation

31.5±3.4

8.8±1.5

43.7±4.2

64.8±5.6

62.5±4.4

77.6±4.3

6 months after operation

6.5±1.9*

2.5±2.2*

6.0±2.4*

15.5±3.3*

29.4±3.5*

37.1±4.3*

12 months after operation

7.1±2.1*

2.9±1.9*

5.4±2.6*

14.6±4.1*

28.9±4.1*

37.8±4.7*

MPQ: McGill pain questionnaire; VAS: visual analog scale; HRSD: Hamilton Rating Scale for Depression; HAMA: Hamilton Anxiety Scale; SAS: Self-rating Anxiety Scale; SDS: Self-rating Depression Scale. *P <0.01 vs pre-operation.

Complications

The main postoperative complications were transient slight hemiplegia (8 cases), hypesthesia and paresthesia (15), slight deep sensory disability in the lower limbs (4), and a bearing down feeling of the affected extremity (6) on the operative side. Thirteen cases had a transient hyperalgesia in the upper chest.

Muscle strength recovered and hypesthesia and paresthesia disappeared in most patients by 3 weeks after DREZ coagulation. At 6-month follow-up, slight numbness occurred in the dermatomes of the T2-4 spinal segment (2 cases), palm (2) and toes on operation side. The bearing down feeling in 6 cases had not changed. At 12-month follow-up, only 1 case had toe numbness, but the bearing down feeling in 6 cases still remained. One patient died from pulmonary infection 2 months after operation.

DISCUSSION

The injury of spinal dorsal roots is commonly seen in traumatic neural root damage, avulsion and vertebral fractures. Some patients experience intractable pain in the dermatomes of damaged spinal dorsal roots, the mechanism of which is still unclear at present. Several studies2 show that loss of inhibition of large-caliber sensory fibers after dorsal root damage may result in the deafferentation of nociception-transmitting neurons in the dorsal horn, and thus produce neuronal hyperactivity and hypersensitivity. The deafferented neurons produce abnormal spontaneous discharges and retrograde discharges with intermittent bursts of high-frequency activities. The properties of those discharges are consistent with the characteristics of deafferentation pain, which usually is a continuous pain accompanied by episodes of sharp exacerbation. In addition, scars in the dorsal horn from rootlet rupture and gliosis in the substantia gelatinosa also cause pain.

Some researchers propose that deafferentation pain is related to biochemical processes taking place in the dorsal horn,3 i.e., substance P receptors, N-methyl-d-aspartate receptor activity, slow calcium channels and β-endorphin- like substances.4

In 1952, Rexed described 10 separate layers in the spinal gray matter, and that the superficial layers 1-5 were related to the outcome of the DREZ operation.5 Neurons in layers 1, 2 and 5 receive major nociceptive inputs and send out fibers known as the spinothalamic tract. The tract of Lissauer is located dorsolateral to the dorsal horn, and about one-third to one-half of the fibers in this tract compose the dorsal root afferent fibers. This tract plays an important role in the central conduction of pain and temperature sensation. The aim of DREZ coagulation is to destroy the Rexed layers 1, 2 and 5, and the medial part of Lissauer’s tract. The lateral nociceptive and central myotactic afferent fibers connecting the motor neurons are selectively cut, while the majority of medial fibers and inhibitive circuitry of Lissauer’s tract and dorsal horn are preserved in the DREZ operation.

In the 1960s, it was revealed that the first level of modulation of nociceptive stimuli was at the DREZ and, based on this theory, the first DREZ coagulation was performed by Sindou in 1972.6 In 1976, this procedure was improved by Nashold et al.7 They destroyed the spinal dorsal horn by thermocoagulation. It was supposed that some types of pain arose from pathological lesions of secondary sensory neurons in the dorsal horn. Because these neurons do not conduct normal, peripheral, afferent impulses, their abnormal function may produce pain. Destruction of these hyperexcitatory neurons by thermocoagulation can eliminate the nociceptive sensation generated in the spinothalamic tract.

Some researchers reported that about 58%–90% patients with deafferentation pain obtained relief from the operation.8-10 Friedman et al11 reported that 82% of the patients with brachial plexus avulsion gained long-term pain relief, while in our study 47.8% obtained complete pain relief immediately after DREZ operation. In our 12-month follow-up study, 26.1% of the cases still maintained complete pain relief, and the average decrease of MPQ and VAS scores in 17 cases was as high as 50% with about 50% of all cases decreased by 75% in MPQ and VAS scores. No patients in our study needed analgesics after surgery. Over half of the cases once had thoughts of, or behavior consistent with, suicide. After operation their anxiety and depression symptoms caused by pain clearly diminished and their quality of life was greatly improved. Equipment for applying thermo- coagulation, ultrasound or laser therapy have been used for the DREZ operation.12-14 However, we used bipolar forceps without recourse to special equipment, a method easy to manipulate for the neurosurgeon.

The DREZ operation has been applied to the treatment of various pain syndromes, such as pain caused by brachial plexus avulsion, spinal cord and/or cauda equina lesions and peripheral nerve injuries and pain in the stump after limb amputation, phantom limb, postherpetic period, reflex sympathetic dystrophy and syringomyelia. Currently, the indications for the DREZ operation are very clear. The outcome is best in the treatment of deafferentation pain, but not as good as in cancer pain and peripheral nerve pain; such as pain after peripheral nerve injury or pain in the stump after limb amputation.

The inclusion criteria in our study are phantom limb pain, pain after brachial plexus avulsion, pain after spinal cord and cauda equina injury (these materials are not discussed in this study). The exclusion criteria are thalamic pain caused by thalamic hemorrhage or infarct, pain caused by spinal tumor, pain after complete spinal transsection, pain covering the area beyond the spinal injury level.

To guarantee a successful DREZ operation, the first important task is to identify the dorsolateral sulcus of the spinal cord correctly, which is easy in the normal spinal cord. Nonetheless, patients with pain usually had a history of severe trauma which could result in ischemia, atrophy, displacement and rotation of the spinal cord, and/or avulsion of dorsal roots. Therefore, identifying the dorsolateral sulcus becomes technically difficult in those conditions. In our experience, sufficient exposure of the normal dorsal roots on the same level of avulsed ones is necessary, and then the dorsolateral sulcus can be identified from normal spinal cord. Second, the angle of dorsolateral sulcus discission should be about 45º to the sagittal plane. Proper adjusting of the angle is particularly important in case of a rotated spinal cord. Usually 3 mm is enough for the depth of dorsolateral sulcus discission, but less depth should be applied in the case of atrophy spinal cord. The landmark for discission depth is the gray matter at the top of the posterior horn. Third, thermocoagulation is performed along the gray matter in discissed sulcus using a bipolar forceps with a slender tip (5 mm exposure of tip) using the lowest power to avoid the heat effect and postoperational edema. The DREZ operation should cover the spinal cord area whose upper/lower edges are one segment higher/lower than the pain level.

In this study, most cases had transient postoperative complications including those observed in the ipsilateral limb; such as hypesthesia and paresthesia (15 cases), slight hemiplegia (8), bearing down feeling of affected extremity (6) and deep sensory disability in lower limbs (4) on the operated side. These complications were possibly due to the thermal effect of the bipolar forceps and edema around the coagulation lesion (confirmed by MRI after operation). Traction or damage of residual spinal vessels within the operating area may also result in decreased blood supply of the spinal tract such as corticospinal, spinothalamic tract, or fasciculus gracilis and cuneatus. At 12-month follow-up, 1 case still had slightly diminished sensation in the toes. The bearing-down feeling in the affected extremities in 6 cases had no change, which is supposedly related to partial damage of deep sensory fibers. One patient died of pulmonary infection and respiratory failure. He suffered from long-term chronic bronchitis and, postoperatively, prolonged mechanical ventilation for hypoxemia led to respiratory alkalosis. The DREZ coagulation of C5-T1 could also have affected his pulmonary function adversely. In conclusion, exact identification of the spinal dorsolateral sulcus, discission of the spinal cord strictly along the dorsolateral sulcus, discission depth of less than 3 mm, avoiding damage or traction of residual spinal vessels and using the lowest power of bipolar thermocoagulation are the keys to avoiding severe complications. Furthermore, intensive intra-operative monitoring of the spinal motor and sensory functions is beneficial for reducing complications.15,16

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(Received February 14, 2008)

Edited by SHEN Xi-bin

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