Analgesia: Brief Report
The lumbar intervertebral disk accounts for 39% of chronic low back pain.1 Diskogenic pain is believed to originate from internal disk disruptions2 and is mainly mediated by the sinuvertebral nerve, situated in the epidural space close to the posterior aspect of the disk.3 The current diagnostic gold standard is provocation diskography, which is a controversial procedure because of potential false-positive results.4 Diagnostic nerve block, which is well established for zygapophysial joint pain,5,6 would possibly compensate for some of the disadvantages of diskography and provide an alternative. The aim of this exploratory study was to evaluate the sensitivity and target specificity of sinuvertebral nerve blockade (SVNB) for the diagnosis of lumbar diskogenic pain in comparison with provocation diskography, the current gold standard.
The study was approved by the local ethics committee. Written informed consent was obtained from all patients.
Patients with suspected diskogenic pain who were referred by orthopedic surgeons for segmental diagnosis were studied. Interventional diagnostic procedures were performed as part of a multidisciplinary medical consultation involving physiotherapists, orthopedic surgeons, rheumatologists, and psychiatrists. Inclusion criteria were low back pain for >6 months, no effect from nonopioid analgesics/coanalgesics and physical therapy, normal blood coagulation, no focal infections, no fever, no pregnancy, pain ≥2.5 on the VAS (visual analog scale: 0 = no pain, 10 = worst pain imaginable), and one or two positive disks as assessed by diskography.
Fifteen patients fulfilled the inclusion criteria and consented to SVNB. For descriptive purposes, patients were evaluated for pain duration, current VAS score, and scores on the Beck Depression Inventory and Short Form 36.
Diskography was performed according to the International Spine Intervention Society standards for lumbar disk stimulation.7 Nonionic contrast medium (Iohexol 300 mg/mL) and antibiotics (cefazoline 100 mg or clindamycin 6 mg intradiscally) were used. Pain during diskography was rated on a 0-to-10 numerical rating scale (0 = no pain, 10 = worst pain imaginable), and intradiscal pressure was monitored. Diskography was considered positive when all the International Spine Intervention Society criteria were fullfilled7: concordant pain upon stimulation, with a numerical rating scale ≥7 and at a pressure ≤50 psi above opening pressure, no pain, discordant pain, or pain at >50 psi above opening pressure on at least 1 adjacent disk.
Sinuvertebral Nerve Block
In patients with 1 to 2 positive disks, SVNB was performed with computed tomography-controlled interlaminar epidural infiltration with bupivacaine 0.5% and contrast medium (Iopamidol 300) 2:1, using two 22-gauge spinal needles (Fig. 1). Spread of the injectant was documented immediately after the procedure by a spiral computed tomography scan, including the adjacent levels. Ideal spread of injectant is shown in Figure 2. Sensitivity to cold at L3 to S1 dermatomes, VAS, and type of physical restrictions (1 to 3 actions or movements that patients were unable to perform because of pain) were recorded before the block and 30 minutes for 2 hours after the block. After SVNB, patients performed the aforementioned actions or movements and rated their improvement as none, moderate, or excellent. Successful block was defined as ≥80% VAS decrease within the first 30 minutes or excellent relief of physical restrictions.
We sought results that would be compatible with a sensitivity and target specificity of 80%. Analyzing 15 patients would result in a 95% confidence interval (CI) of 60%–100%. Sensitivity was defined as the number of successful blocks divided by the number of all blocks. Target specificity was defined as the proportion of blocks in which contrast medium did not reach nerve roots or adjacent disks.
Patient characteristics are shown in Table 1; SVNB results are presented in Table 2.
Pain reduction ≥80% was observed in 8/15 patients. Three additional patients had 78%, 76%, and 33% pain reduction, but reported excellent relief of physical restrictions. The sensitivity of SVNB was thus 73.3% (95% CI: 50.9% to 95.7%). Details of target specificity are presented in Table 3. The injectant spread to the cranial segment only in 1 case. Spread to the intervertebral foramina with contact to the nerve roots was seen in 8 patients. Subdural spread occurred once. However, hypoesthesia to cold at the corresponding dermatomes was found in only 2 of those patients (Table 3). The block was target specific in 6/15 patients (40%; 95% CI: 15.2% to 64.8%). The dural sac was accidentally punctured in 3 patients; self-limited postpuncture headache occurred once.
The sensitivity of SVNB was 73%, which lies well within the 95% CI for a sensitivity of 80% (60%–100%). The 95% CI of target specificity was 15.2% to 64.8%, which only marginally overlaps the 95% CI of the desired target specificity of 80% (which is 60%–100%).
The pain-blocking potency of SVNB seems to be similar to that of intradiscal application of local anesthetics,8 which in combination with our 73% positive rate, indicates that the main afferent pathways for diskogenic pain are the sinuvertebral nerves and its branches. The possible reasons why not all patients benefited from SVNB were (a) nociceptive input partially mediated by the ramus communicans griseus to the lumbar sympathetic trunk; (b) possible concomitant anterior internal disk disruptions whose nociceptive signal is conducted via the anterior pathway, which was not anesthetized; or (c) false-positive response to diskography.
Foraminal diffusion and nerve root contact were frequent (53.3%) and a major reason for the modest target specificity. Interestingly, the observed areas of hypoesthesia after the intervention did not correspond to the dermatomes of the affected nerve roots (Table 3). The amount of local anesthetic was possibly insufficient to produce a complete dermatomal pattern, and therefore the spread to the root might not have substantially affected the diagnostic specificity of the block.
In conclusion, SVNB is currently unlikely to replace provocation diskography. However, the results of the present study encourage further investigation. Considering that diskography may produce false-positive results and accelerate degeneration of healthy disks,9 alternative research procedures are warranted. Future research should also investigate the diagnostic specificity of SVNB and include improvements in the technique by reducing the incidence of dural puncture.
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© 2010 International Anesthesia Research Society
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