Andreas Siegenthaler

The prevalence of widespread central hypersensitivity in chronic pain patients

Chronic pain is associated with generalized hypersensitivity and impaired endogenous pain modulation (conditioned pain modulation; CPM). Despite extensive research, their prevalence in chronic pain patients is unknown. This study investigated the prevalence and potential determinants of widespread central hypersensitivity and described the distribution of CPM in chronic pain patients.

What does local tenderness say about the origin of pain? An investigation of cervical zygapophysial joint pain.

BACKGROUND: Mechanical pain sensitivity is assessed in every patient with pain, either by palpation or by quantitative pressure algometry. Despite widespread use, no studies have formally addressed the usefulness of this practice for the identification of the source of pain. We tested the hypothesis that assessing mechanical pain sensitivity distinguishes damaged from healthy cervical zygapophysial (facet) joints. METHODS: Thirty-three patients with chronic unilateral neck pain were studied. Pressure pain thresholds (PPTs) were assessed bilaterally at all cervical zygapophysial joints. The diagnosis of zygapophysial joint pain was made by selective nerve blocks. Primary analysis was the comparison of the PPT between symptomatic and contralateral asymptomatic joints. The secondary end points were as follows: differences in PPT between affected and asymptomatic joints of the same side of patients with zygapophysial joint pain; differences in PPT at the painful side between patients with and without zygapophysial joint pain; and sensitivity and specificity of PPT for 2 different cutoffs (difference in PPT between affected and contralateral side by 1 and 30 kPa, meaning that the test was considered positive if the difference in PPT between painful and contralateral side was negative by at least 1 and 30 kPa, respectively). The PPT of patients was also compared with the PPT of 12 pain-free subjects. RESULTS: Zygapophysial joint pain was present in 14 patients. In these cases, the difference in mean PPT between affected and contralateral side (primary analysis) was −6.2 kPa (95% confidence interval: −19.5 to 7.2, P = 0.34). In addition, the secondary analyses yielded no statistically significant differences. For the cutoff of 1 kPa, sensitivity and specificity of PPT were 67% and 16%, respectively, resulting in a positive likelihood ratio of 0.79 and a diagnostic confidence of 38%. When the cutoff of 30 kPa was considered, the sensitivity decreased to only 13%, whereas the specificity increased to 95%, resulting in a positive likelihood ratio of 2.53 and a diagnostic confidence of 67%. The PPT was significantly lower in patients than in pain-free subjects (P < 0.001). CONCLUSIONS: Assessing mechanical pain sensitivity is not diagnostic for cervical zygapophysial joint pain. The finding should stimulate further research into a diagnostic tool that is widely used in the clinical examination of patients with pain.

Ultrasound imaging to estimate risk of esophageal and vascular puncture after conventional stellate ganglion block.

Background and Objectives The most common techniques to perform stellate ganglion blocks (SGBs) are the blind C6 approach and the fluoroscopic-controlled paratracheal C7 approach, both after manual dislocation of the large vessels. Complications due to vascular or esophageal puncture have been reported. The goal of this ultrasound imaging study was to determine how frequently hazardous structures are located along the needle path of conventional SGB and to determine the influence of the dislocation maneuver on their position. Methods Sixty volunteers were examined on both sides. The presence of the esophagus, vertebral artery, and other arteries located within the needle path of an SGB at the C6 and C7 levels was determined before and during the dislocation maneuver. Results On the left side, the esophagus was located along the needle path in 22 and 39 of 60 cases at the C6 and C7 levels, respectively, and remained there in 10 and 22 of 60 cases during dislocation. The esophagus appeared in the needle path during dislocation from a previously safe location in 5 and 8 of these cases at the C6 and C7 locations, respectively. The vertebral artery was located in the needle path in a range of 2 to 8 of 60 cases without impact of dislocation on its position. Other arteries were located in the needle path in the range of 10 to 17 of 60 cases with a slight decrease during dislocation. Conclusions The esophagus and relevant arteries were frequently located in the needle path of conventional SGBs. The dislocation maneuver had a partial impact on moving these structures away from the target and may increase left-sided esophageal puncture risk in certain individuals. Ultrasound (US) imaging is expected to improve the safety of SGB, but it will require clinical trials to confirm this expectation.

Accuracy of ultrasound-guided nerve blocks of the cervical zygapophysial joints.

Background: Cervical zygapophysial joint nerve blocks typically are performed with fluoroscopic needle guidance. Descriptions of ultrasound-guided block of these nerves are available, but only one small study compared ultrasound with fluoroscopy, and only for the third occipital nerve. To evaluate the potential usefulness of ultrasound-guidance in clinical practice, studies that determine the accuracy of this technique using a validated control are essential. The aim of this study was to determine the accuracy of ultrasound-guided nerve blocks of the cervical zygapophysial joints using fluoroscopy as control. Methods: Sixty volunteers were studied. Ultrasound-imaging was used to place the needle to the bony target of cervical zygapophysial joint nerve blocks. The levels of needle placement were determined randomly (three levels per volunteer). After ultrasound-guided needle placement and application of 0.2 ml contrast dye, fluoroscopic imaging was performed for later evaluation by a blinded pain physician and considered as gold standard. Raw agreement, chance-corrected agreement &kgr;, and chance-independent agreement &PHgr; between the ultrasound-guided placement and the assessment using fluoroscopy were calculated to quantify accuracy. Results: One hundred eighty needles were placed in 60 volunteers. Raw agreement was 87% (95% CI 81–91%), &kgr; was 0.74 (0.64–0.83), and &PHgr; 0.99 (0.99–0.99). Accuracy varied significantly between the different cervical nerves: it was low for the C7 medial branch, whereas all other levels showed very good accuracy. Conclusions: Ultrasound-imaging is an accurate technique for performing cervical zygapophysial joint nerve blocks in volunteers, except for the medial branch blocks of C7.

Ultrasound anatomy of the nerves supplying the cervical zygapophyseal joints: an exploratory study.

Background and Objectives: Nerve blocks and radiofrequency neurotomy of the nerves supplying the cervical zygapophyseal joints are validated tools for diagnosis and treatment of chronic neck pain, respectively. Unlike fluoroscopy, ultrasound may allow visualization of the target nerves, thereby potentially improving diagnostic accuracy and therapeutic efficacy of the procedures. The aims of this exploratory study were to determine the ultrasound visibility of the target nerves in chronic neck pain patients and to describe the variability of their course in relation to the fluoroscopically used bony landmarks. Methods: Fifty patients with chronic neck pain were studied. Sonographic visibility of the nerves and the bony target of fluoroscopically guided blocks were determined. The craniocaudal distance between the nerves and their corresponding fluoroscopic targets was measured. Results: Successful visualization of the nerves varied from 96% for the third occipital nerve to 84% for the medial branch of C6. The great exception was the medial branch of C7, which was visualized in 32%. The bony targets could be identified in all patients, with exception of C7, which was identified in 92%. The craniocaudal distance of each nerve to the corresponding bony target varied, the upper limit of the range being 2.2 mm at C4, the lower limit 1.0 mm at C7. Conclusions: The medial branches and their relation to the fluoroscopically used bony targets were mostly visualized by ultrasound, with the exception of the medial branch of C7 and, to a lesser extent, the bony target of C7. The nerve location may be distant from the fluoroscopes target. These findings justify further studies to investigate the validity of ultrasound guided blocks for invasive diagnosis/treatment of cervical zygapophyseal joint pain.

Does acupuncture needling induce analgesic effects comparable to diffuse noxious inhibitory controls

Diffuse noxious inhibitory control (DNIC) is described as one possible mechanism of acupuncture analgesia. This study investigated the analgesic effect of acupuncture without stimulation compared to nonpenetrating sham acupuncture (NPSA) and cold-pressor-induced DNIC. Forty-five subjects received each of the three interventions in a randomized order. The analgesic effect was measured using pressure algometry at the second toe before and after each of the interventions. Pressure pain detection threshold (PPDT) rose from 299 kPa (SD 112 kPa) to 364 kPa (SD 144), 353 kPa (SD 135), and 467 kPa (SD 168) after acupuncture, NPSA, and DNIC test, respectively. There was no statistically significant difference between acupuncture and NPSA at any time, but a significantly higher increase of PPDT in the DNIC test compared to acupuncture and NPSA. PPDT decreased after the DNIC test, whereas it remained stable after acupuncture and NPSA. Acupuncture needling at low pain stimulus intensity showed a small analgesic effect which did not significantly differ from placebo response and was significantly less than a DNIC-like effect of a painful noninvasive stimulus.

First water vapor measurements at 183 GHz from the high alpine station Jungfraujoch

During six months in 1999, we observed the water vapor emission line at 183.31 GHz with a microwave radiometer at the high alpine site Jungfraujoch in Switzerland. We retrieved statistics on the atmospheric transmission and profiles of stratospheric water vapor on selected days. Our site seems well suited for observations of this spectral line.

Reliability of quantitative sensory tests in a low back pain population

Background and Objectives Reliability is an essential condition for using quantitative sensory tests (QSTs) in research and clinical practice, but information on reliability in patients with chronic pain is sparse. The aim of this study was to evaluate the reliability of different QST in patients with chronic low back pain. Methods Eighty-nine patients with chronic low back pain participated in 2 identical experimental sessions, separated by at least 7 days. The following parameters were recorded: pressure pain detection and tolerance thresholds at the toe, electrical pain thresholds to single and repeated stimulation, heat pain detection and tolerance thresholds at the arm and leg, cold pain detection threshold at the arm and leg, and conditioned pain modulation using the cold pressor test. Reliability was analyzed using the coefficient of variation, the coefficient of repeatability, and the intraclass correlation coefficient. It was judged as acceptable or not based primarily on the analysis of the coefficient of repeatability. Results The reliability of most tests was acceptable. Exceptions were cold pain detection thresholds at the leg and arm. Conclusions Most QST measurements have acceptable reliability in patients with chronic low back pain.

A Shortened Radiofrequency Denervation Method for Cervical Zygapophysial Joint Pain Based on Ultrasound Localization of the Nerves

OBJECTIVE   Radiofrequency neurotomy is a recognized treatment for cervical zygapophysial joint pain. In several studies, the method has provided complete pain relief in 60-70% of the patients for approximately 9 months. The validated technique has the disadvantage of procedural times of 2-4 hours because several lesions are performed to take into account the variable nerve course. We tested the hypothesis that ultrasound localization of the nerves would enable us to reduce the number of lesions performed, while reaching the benchmark of at least 80% pain relief in 80% of patients with a median duration of 35 weeks, as achieved by a previous investigation using the standard method. INTERVENTIONS   We prospectively studied 15 consecutive patients with diagnosed cervical zygapophysial joint pain. They were treated using a shortened radiofrequency procedure under fluoroscopic control, based on previous ultrasound localization of the joint supplying nerves, with only two thermal lesions performed per nerve. Successful treatment was defined as at least 80% pain relief in the visual analog scale as compared with pretreatment. Follow-up was performed until 12 months after treatment. RESULTS   Of the 15 patients, 14 were successfully treated (93%, 95% confidence interval [CI] 80-100%) with a median time of pain relief of 44 weeks. At 6 and 12 months, 13 (87%, 95% CI 70-100%) and 6 patients (40%, 95% CI 15-65%) reported successful treatment, respectively. The median duration of the procedure was 35 minutes. CONCLUSION   In patients with cervical zygapophysial joint pain, radiofrequency denervation according to a shortened protocol based on ultrasound localization of the nerves reached the benchmark of the standard technique.

Linking altered central pain processing and genetic polymorphism to drug efficacy in chronic low back pain.

BackgroundInability to predict the therapeutic effect of a drug in individual pain patients prolongs the process of drug and dose finding until satisfactory pharmacotherapy can be achieved. Many chronic pain conditions are associated with hypersensitivity of the nervous system or impaired endogenous pain modulation. Pharmacotherapy often aims at influencing these disturbed nociceptive processes. Its effect might therefore depend on the extent to which they are altered. Quantitative sensory testing (QST) can evaluate various aspects of pain processing and might therefore be able to predict the analgesic efficacy of a given drug. In the present study three drugs commonly used in the pharmacological management of chronic low back pain are investigated. The primary objective is to examine the ability of QST to predict pain reduction. As a secondary objective, the analgesic effects of these drugs and their effect on QST are evaluated.Methods/DesignIn this randomized, double blinded, placebo controlled cross-over study, patients with chronic low back pain are randomly assigned to imipramine, oxycodone or clobazam versus active placebo. QST is assessed at baseline, 1 and 2 h after drug administration. Pain intensity, side effects and patients’ global impression of change are assessed in intervals of 30 min up to two hours after drug intake. Baseline QST is used as explanatory variable to predict drug effect. The change in QST over time is analyzed to describe the pharmacodynamic effects of each drug on experimental pain modalities. Genetic polymorphisms are analyzed as co-variables.DiscussionPharmacotherapy is a mainstay in chronic pain treatment. Antidepressants, anticonvulsants and opioids are frequently prescribed in a “trial and error” fashion, without knowledge however, which drug suits best which patient. The present study addresses the important need to translate recent advances in pain research to clinical practice. Assessing the predictive value of central hypersensitivity and endogenous pain modulation could allow for the implementation of a mechanism-based treatment strategy in individual patients.Trial registrationClinicaltrials.gov, NCT01179828