MULTIDISCIPLINARY PAIN ABSTRACTS: 7

Clinical reports suggest that opioids, intended to abolish pain, can unexpectedly produce hyperalgesia. This paradoxical effect may be mechanistically related to tolerance induced by increasing doses of opioids. Two case reports illustrate a syndrome characterized by increasing pain pursued by escalating opioid doses, which results in a worsening of the clinical picture. Several experimental data may help explain the course of this challenging clinical condition. In escalating opioid doses rapidly, a risk of opioid-induced hyperalgesia should be recognized, as higher doses of opioids may stimulate rather than inhibit the central nervous system by different mechanisms. Alternative procedures should be taken into consideration to break this cycle, should it occur. More data are needed to detect this condition, as currently no diagnostic information on specific markers, clinical or biochemical, exists.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 4

Stellate ganglion block is a procedure frequently used for the management of patients with chronic sympathetically mediated pain affecting the arm, neck or head. In this study, the authors looked at the effect of the stellate ganglion block on ipsilateral phrenic nerve function, and hence diaphragmatic strength, in 11 adult patients with chronic sympathetically mediated pain. Pre-block and post-block forced vital capacity (FVC) measurements were recorded using a pneumotachograph and a Magstim nerve stimulator was used to generate pre-block and post-block twitch mouth pressures (P[TWM]). This device can be used to stimulate the phrenic nerves and hence the diaphragm. The resulting change in airway pressure was measured at the mouth and has previously been shown to reflect diaphragm strength. There was no statistically significant difference in FVC or P(TWM) before or after the stellate ganglion block. In conclusion, a stellate ganglion block has no adverse effect on ipsilateral phrenic nerve function or diaphragm strength in healthy adult patients.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 12

The purpose of this study was to investigate whether selective nerve fiber dysfunction, as assessed by quantitative sensory testing (QST), correlates with the effectiveness of epidural steroid injections (ESI) in patients with lumbar radiculopathy. Twenty patients with unilateral painful sciatica caused by disc herniation participated in this open study. Before ESI, quantitative thermal and mechanical sensory testing was conducted at the most painful dermatome and the contralateral dermatome. The primary outcome measure used was the self-recording of pain intensity twice daily with a 0–10 numerical pain scale (NPS). Secondary efficacy measures included the Short Form of the McGill Pain Questionnaire, the straight leg raising test, and the lumbar range of motion. A significant difference in all types of sensory thresholds between the affected and the contralateral dermatomes was detected at baseline. All outcome measures improved subsequent to the ESI. A significant positive correlation was found between the increase in cold sensation thresholds of the affected dermatome (Adelta-fiber dysfunction) and the improvement in NPS. The increase in touch and vibration thresholds (Abeta-fiber dysfunction) was found to be inversely correlated with the improvement in NPS. No correlation was found between heat sensation thresholds and any of the outcome measures. These results suggest that QST has the potential to be an important tool in the selection of the appropriate treatment for patients with sciatica and may assist in identifying the mechanisms of pain generation in these patients.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 33

The authors describe the effectiveness of motor cortex stimulation (MCS) in a patient with complex regional pain syndrome (CRPS) type II, formerly known as causalgia, with hemibody allodynia. During MCS, a subjective sensation of warm paresthesia developed in the painful hand and forearm and spread toward the trunk. Pain and allodynia in the areas associated with this sensation were alleviated significantly. The analgesic effect of stimulation proved to be long lasting and was still present at the 12-month follow up. The authors speculate that MCS might exert its effect through the modulation of thalamic activity in this particular case of CRPS with hemisensory deficit. A central mechanism associated with functional disturbance in noxious-event processing in the thalamus might have an important role in the pathogenesis of the condition.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 38

The nerve roots and the dorsal root ganglion (DRG) play an important role in the pain mechanisms of patients suffering from chronic low back pain. Signs of demyelination and increased sensitization for stimuli occur after a direct nerve root trauma, and the plasticity for the DRG also may change the response to a given peripheral stimuli when repeated frequently over a long period of time. The regeneration mechanisms of spinal nerve roots and DRG regarding function are slow, and the final grade of recurrence depends on the degree of injury. The limited regeneration mechanisms for nerve injury and the fact that "established chronic pain centers" are hard to influence after a long pain history favor an aggressive strategy for pain management. Today, a number of treatment strategies exist for chronic low back pain patients (with or without a diagnosed nerve root injury). These strategies include physiotherapy, nonsteroid anti-inflammatory drugs (NSAIDs), steroids, analgesics of different types and administration routes, surgery, and other sorts of invasive treatments. Further knowledge about the nerve root, DRG, and the rest of the nervous system in these patients is necessary.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 16

The present double-blind, placebo-controlled study was designed to test quantitatively the effect and of nerve growth factor (NGF) injected into the masseter muscle. Pressure pain thresholds (PPT) and pressure tolerance thresholds (PTOL) were used as indices of mechanical allodynia and hyperalgesia in the jaw-closing muscles. In addition, perceived pain intensity was assessed by the subjects on a 0 to 10 numerical rating scale (NRS) with the jaw at rest and in relation to various oral functions (chewing, yawning, talking, swallowing, drinking and smiling). Repeated measures analysis of variance (ANOVA) was used to test for significant effects. Injection of NGF into the masseter muscle was associated with significantly reduced PPT for 7 days and PTOL for 1 day. Buffered isotonic saline injections into the masseter muscle also significantly lowered the PPT after 1 day and isotonic saline had no significant effect on PTOL. In contrast, assessment of PPT and PTOL in the noninjected temporalis muscles demonstrated a significant increase after 14 to 28 days, which may have reflected an adaptation to the test procedure. NRS scores of chewing and yawning were significantly increased for 7 days following NGF injection. Systemic adverse effects were noted in one subject who reported fever and slight discomfort about 8 hours after the NGF injection. In conclusion, this is the first study to show that injection of NGF into the human masseter muscle causes local signs of mechanical allodynia and hyperalgesia that persist for at least 7 days as well as pain during strenuous jaw movement. The present pain model is safe and may be used to gain further insight into the neurobiological mechanisms of muscle pain and sensitization.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 20

Trigeminocervical reflex is a brainstem reflex that is evoked by stimulating the sensory branches of the trigeminal nerve and can be recorded from the neck muscles. Electric stimulation of the supraorbital nerve evokes a reflex response (C3) and early reflex response (C1). The mean latencies of C1 and C3 of patients with parallel fibers (PFS) were compared with normal values. In healthy volunteers, C3 latency ± standard deviation was 54.17 ± 6.00 ms ipsilaterally and 51.25 ± 9.26 ms contralaterally. The difference was not significant. The C1 latency was 17.46 ± 4.89 ms. In patients with PFS, C1 latency was 13.83 ± 4.48 ms and the C3 latency was 62.70 ± 18.22 ms. The difference was not significant between the patients and healthy volunteers. Conclude in patients with PFS having neck pain, trigeminocervical connections were not influenced and some other mechanisms may be responsible for pain in these patients.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 9

The aim of this study was to identify characteristics of patients treated with opioids that distinguish them from similar patients not treated with opioids in a large population of patients with spine and radicular pain, and to determine the prevalence of opioid use. Overall, 3.4% of the patients had opioids included in their plan of care. There was no difference in age, gender, education, or compensation status between the two groups. Patients were more likely to be treated if the duration of their symptoms had been less than 3 months. However, 75% of the patients with opioids in their plan had experienced symptoms longer than 3 months. A greater incidence of objective findings was identified in the opioid group. The authors cannot comment on the prevalence of opioid use because, to the best of their knowledge, no other similar studies are available for comparison.