Epidural clonidine analgesia for intractable cancer pain. The Epidural Clonidine Study Group

Clonidine and guanfacine-induced antinociception in visceral pain: possible role of α2/I2 binding sites

Visceral pain is one of the most common forms of pain which is poorly understood. We now studied the influence of imidazoline/guanidinium compounds such as clonidine and guanfacine on visceral pain in the presence or absence of yohimbine and benazoline. To produce visceral pain-related behaviours, formalin (10%) was administered by inserting a fine cannula into the colon via the anus. Each experiment took 1 h. Clonidine (0.001, 0.01 and 0.1 mg/kg, i.p.) and guanfacine (2.5, 5 and 10 mg/kg, i.p.) produced analgesia dose dependently. The clonidine response was inhibited by yohimbine (0.2 mg/kg, i.p.). On the other hand, benazoline (5 mg/kg, i.p.) blocked the antinociceptive effect of guanfacine (5 mg/kg). Benazoline (2.5 and 5 mg/kg) itself also induced analgesia in inflammatory colonic pain. In this study, we used morphine to ensure that the behavioural responses were pain-related. Our results showed that morphine (2.5, 5 and 10 mg/kg, s.c.) produced a dose-dependent antinociception. The morphine (7 mg/kg, s.c.) response was reduced by naloxone (2 mg/kg, i.p.). However, we concluded that both imidazoline (I(2)) and alpha(2)-adrenoceptors may play a role in producing analgesia in visceral pain.

Adjuvant Analgesics in Cancer Pain Management

Adjuvant analgesics are defined as drugs with a primary indication other than pain that have analgesic properties in some painful conditions. The group includes numerous drugs in diverse classes. Although the widespread use of these drugs as first-line agents in chronic nonmalignant pain syndromes suggests that the term "adjuvant" is a misnomer, they usually are combined with a less-than-satisfactory opioid regimen when administered for cancer pain. Some adjuvant analgesics are useful in several painful conditions and are described as multipurpose adjuvant analgesics (antidepressants, corticosteroids, alpha(2)-adrenergic agonists, neuroleptics), whereas others are specific for neuropathic pain (anticonvulsants, local anesthetics, N-methyl-D-aspartate receptor antagonists), bone pain (calcitonin, bisphosphonates, radiopharmaceuticals), musculoskeletal pain (muscle relaxants), or pain from bowel obstruction (octreotide, anticholinergics). This article reviews the evidence supporting the use of each class of adjuvant analgesic for the treatment of pain in cancer patients and provides a comprehensive outline of dosing recommendations, side effects, and drug interactions.

Evolving spinal analgesia practice in palliative care

Intraspinal analgesia can be helpful in some patients with intractable pain. Over 15 years palliative care professionals evolved their spinals policy through a repeated series of evaluations, discussions and literature reviews. One hundred intraspinal lines were then reviewed. Notable changes in policy were the switch from epidurals to intrathecals, and the insertion of lines during working hours rather than as emergencies. Our efficacy, and frequency of adverse effects, is equal or better to published studies. Key issues in reducing adverse effects were the improved care of the spinal line exit site, a change from bolus administration to continuous infusions, and modifying line insertion techniques. Current policy is to use continuous infusions of diamorphine and bupivacaine in a 1:5 ratio through externalized intrathecal lines. The lines are effective in approximately two thirds of patients and can be kept in place for up to 18 months. The policy continues to be updated and common documentation is now in place.

Intrathecal clonidine potentiates suppression of tactile hypersensitivity by spinal cord stimulation in a model of neuropathy

Spinal cord stimulation (SCS) may provide pain relief in approximately 60%-70% of well selected patients with pain caused by peripheral nerve injury. We have previously demonstrated that intrathecal (IT) administration of small doses of certain drugs, both in experimental animals and in patients, significantly enhances the pain-relieving effect of SCS. The alpha2-adrenoceptor agonist, clonidine, is extensively used as an adjunct to spinal morphine and is suggested to be particularly effective for neuropathic pain, but its clinical use is limited by side effects such as sedation and hypotension. In this study, we investigated the dose-response characteristics of IT clonidine, and whether a subeffective dose of clonidine could enhance the effect of SCS in nerve-injured rats with tactile hypersensitivity (allodynia). Results showed that clonidine, in doses of 1-20 microg, reduced the hypersensitivity in a dose-dependent manner. In rats in which SCS per se failed to suppress tactile hypersensitivity, the combination of SCS and a subeffective dose of clonidine appeared to be highly synergistic and markedly attenuated the hypersensitivity. These results suggest that small doses of IT clonidine may be combined with SCS in neuropathic pain patients who do not obtain satisfactory relief with SCS alone.

Attenuation of mechanical allodynia by clinically utilized drugs in a rat chemotherapy-induced neuropathic pain model

Chemotherapy-induced peripheral neuropathy is a common, dose-limiting side effect of cancer chemotherapeutic agents, including the vinca alkaloids such as vincristine. The resulting symptoms, which frequently include moderate to severe pain, can often be disabling. The current study utilized a vincristine-induced neuropathic pain animal model [Pain 93 (2001) 69], in which rats were surgically implanted with mini-osmotic pumps set to deliver vincristine sulfate (30 microg kg(-1)day(-1), i.v.), to examine the time course of progression of various pain modalities and to compare the dose-response effects of clinically utilized drugs on mechanical allodynia to further validate the relevance of this model to clinical pathology. Vincristine infusion resulted in significant cold allodynia after 1 week post-infusion, however mechanical and thermal nociception showed little to no effect. In contrast, marked mechanical allodynia occurred by 1 week of vincristine infusion and returned nearly to pre-infusion levels by the 4th week after infusion pump implantation. ED(50) values (micromol/kg, p.o.) were determined in the mechanical allodynia assay for lamotrigine (82), dextromethorphan (94), gabapentin (400), acetaminophen (1100) and carbamazepine (3600); however, aspirin and ibuprofen had no effects up to 300 and 1000 micromol/kg, respectively. Additionally, ED(50) values (micromol/kg, i.p.) were determined in the mechanical allodynia assay for clonidine (0.35) and morphine (0.62), but desipramine and celecoxib had no effects up to 66 and 260 micromol/kg, respectively. Findings from the current, preclinical study further validate this model as clinically relevant for chemotherapy-induced pain. The surprisingly good effects observed with acetaminophen warrant further investigation of its mechanism(s) of action in neuropathic pain.

Analgesia epidural com clonidina ou romifidina em cães submetidos à cirurgia coxofemoral

Avaliaram-se as alterações cardiorrespiratórias e a analgesia da administração epidural de clonidina ou romifidina em cães submetidos à cirurgia coxofemural. Foram utilizados 14 cães distribuídos em dois grupos: o grupo Cloni recebeu 150µg de clonidina e o grupo Romi, 20µg/kg de romifidina. A indução anestésica foi realizada com propofol e a anestesia cirúrgica mantida com halotano e O2 em respiração espontânea. A punção do espaço epidural foi feita logo após a indução. Antes da indução e a cada 10 minutos foram avaliadas as freqüências cardíaca e respiratória, a pressão arterial sistólica, a saturação de oxigênio da hemoglobina e a concentração de halotano. Após indução e ao término do procedimento cirúrgico coletou-se sangue arterial para avaliação gasométrica de pH, PaCO2, PaO2, SaO2, BE e HCO3-. Foi realizada avaliação pós-operatória do grau de analgesia (intensa, pouco intensa e inadequada) nas primeiras duas horas após término da cirurgia. Os animais do grupo Romi apresentaram bradicardia, bradiarritmias e hipertensão. A freqüência cardíaca e a pressão arterial sistólica no grupo Cloni mantiveram-se dentro da faixa de variação fisiológica para a espécie. A analgesia trans-operatória foi considerada intensa nos dois grupos. A administração epidural de clonidina ou romifidina produziu intensa analgesia transcirúrgica sem depressão respiratória e pouco intensa analgesia pós-operatória por duas horas

Spinal analgesics

The important issues to be emphasized when considering the intrathecal administration of novel analgesics are their proven antinociceptive effect, safety (short- and long-term effects on the spinal cord and potential toxicities), stability in shelf solution and at body temperature by itself, or in combination with other drugs in spinal fluid, compatibility with a long-term spinal infusion pump, whether they are of sufficiently high potency and solubility to be used in the finite volume of an implanted infusion pump, and if a pharmaceutical company is willing to invest the immense resources needed for US Food and Drug Administration approval and subsequent commercial development.

Treatment of neuropathic cancer pain with continuous intrathecal administration of S +-ketamine

The effective treatment of patients suffering from neuropathic cancer pain remains a clinical challenge. When patients experience either insufficient analgesia or problematic side-effects after opioid administration, intrathecal administration of morphine and other medications such as bupivacaine and clonidine may offer significant advantages. Additionally, ketamine, a non-competitive N-methyl-D-Aspartate-receptor antagonist is able to alter pain perception at the spinal level. Because of the potential neurotoxicity after neuraxial use of racemic ketamine, intrathecal administration of the preservative-free active compound, S (+)-ketamine may be a valuable alternative. In this paper, we present a patient with severe neuropathic cancer pain successfully treated by continuous intrathecal infusion of morphine, bupivacaine, clonidine and S (+)-ketamine. Moreover, quality of life measurements before and 3 weeks after the start of spinal treatment revealed an improvement in pain relief and a higher overall quality of life. No clinical signs of neurologic deficit were observed during spinal treatment with S (+)-ketamine. However, the continuous intrathecal administration of S (+)-ketamine should be considered as the last resort because there are no preclinical safety data with relevant concentrations on intrathecal use of S (+)-ketamine.

Opioid effectiveness and side effects in chronic pain

Opioids can provide effective analgesia by way of different routes of administration without limiting side effects for most patients suffering from chronic pain when clinicians properly manage the pertinent patient-, pain-, and drug-centered characteristics. Randomized, placebo-controlled, prospective studies are needed to establish a causal relationship between opioids and hypogonadism. Many of the current studies are retrospective, which only lead to suggestive associations between opioids and hypogonadism and incorporate bias. Clinicians may incorporate available tools, including urine toxicology tests, to assess any aberrant behavior on the part of patients using opioids and to maximize compliance with an opioid regimen.

Long-term intrathecal opioid therapy with a patient-activated, implanted delivery system for the treatment of refractory cancer pain

The present study evaluated the safety and efficacy of patient-activated delivery of intrathecal morphine sulfate boluses delivered by way of a novel internalized intrathecal delivery system. Patients with refractory cancer pain or uncontrollable side effects were enrolled at 17 US and international sites in this prospective, open-label study. Pain relief, reduction in systemic opioid use, and reduction in opioid-related complications were analyzed both individually and together as a measure of overall success. One hundred forty-nine patients were enrolled and 119 were implanted. Average numeric analog scale pain decreased from 6.1 to 4.2 at 1 month and was maintained through month 7 (P <.01) and through month 13 (P <.05). Systemic opioid use was significantly decreased throughout the study (P <.01). Significant reduction in the opioid complication severity index was demonstrated at all 4 follow-up visits (P <.01). Overall success (>/=50% reduction in numeric analog scale pain, use of systemic opioids, or opioid complication severity index) was reported in 83%, 90%, 85%, and 91% of patients at months 1, 2, 3, and 4, respectively. This study demonstrated that patients with refractory cancer pain or intolerable side effects achieved better analgesia when managed with patient-activated intrathecal delivery of morphine sulfate via an implanted delivery system.

Intrathecal, but not intravenous adenosine reduces allodynia in patients with neuropathic pain

Intrathecal adenosine reduces allodynia from intradermal capsaicin in human volunteers, and reduces hypersensitivity to mechanical stimuli in animals with nerve injury. Although both intrathecal and intravenous adenosine have been reported to relieve pain in patients with neuropathic pain, there are no controlled trials of this therapy. In order to determine the effect of adenosine, seven patients with chronic neuropathic pain and stable areas of mechanical hyperalgesia and allodynia were recruited. Using a double-blind, cross-over design, patients were studied on two occasions - once with intrathecal adenosine, 2 mg and once with intravenous adenosine, 2 mg, using saline by the alternate route. Areas of hyperalgesia and allodynia and pain from von Frey stimulation in the area of allodynia were determined up to 24 h after drug injection. Intrathecal, but not intravenous adenosine reduced area of allodynia by approximately 25% (P<0.05) from 2 to 24 h after injection. Intrathecal adenosine reduced pain from von Frey filament stimulation in the area of allodynia by approximately 20% (P<0.05). Ongoing pain was unaffected by adenosine by either route. Intrathecal, but not intravenous adenosine, caused backache in five of seven patients, lasting 6 h. These results indicate that intrathecal adenosine reduces allodynia and pain from stimulation in the area of allodynia, whereas the same dose of adenosine intravenously was ineffective. Given the modest effect and common side effects, the role for intrathecal adenosine as a sole agent for the treatment of neuropathic pain may be limited.

Intrathecal morphine for chronic benign pain

In the treatment of chronic benign pain, the administration of an intrathecal opioid produces a potent analgesia without interfering with the motor and sensory functions of the lower extremities. An intrathecal opioid should be considered only when pain control with conventional oral and systemic administration is inadequate or is associated with unmanageable side effects. A trial period and a psychological evaluation are mandatory prior to implantation of a permanent device. About 40% of the patients need surgical revision for various complications. Hormonal changes may influence sexual behaviour. Catheter granulomas can form with high concentrations of morphine. Adjuvant drugs such as bupivacaine, clonidine and ketamine might be necessary to deal with the development of tolerance to morphine. The sophistication of available technology for intrathecal infusion today far exceeds our knowledge of the potential neurological effects of this treatment modality.

Spinal delivery of analgesics in experimental models of pain and analgesia

Systemic administration of analgesics can lead to serious adverse side effects compromising therapeutic benefit in some patients. Information coding pain transmits along an afferent neuronal network, the first synapses of which reside principally in the spinal cord. Delivery of compounds to spinal cord, the intended site of action for some analgesics, is potentially a more efficient and precise method for inhibiting the pain signal. Activation of specific proteins that reside in spinal neuronal membranes can result in hyperpolarization of secondary neurons, which can prevent transmission of the pain signal. This is one of the mechanisms by which opioids induce analgesia. The spinal cord is enriched in such molecular targets, the activation of which inhibit the transmission of the pain signal early in the afferent neuronal network. This review describes the pre-clinical models that enable new target discovery and development of novel analgesics for site-directed pain management.

Roles of alpha-adrenoceptors and sympathetic nerve in acute herpetic pain induced by herpes simplex virus inoculation in mice

Percutaneous inoculation with herpes simplex virus type-1 brings about herpes zoster-like skin lesions, tactile allodynia, and mechanical hyperalgesia in mice. This study was conducted to determine whether the sympathetic nervous system and alpha-adrenoceptors would be involved in these pain-related responses and whether the alpha(2)-adrenoceptor agonist clonidine would suppress these responses. The adrenergic neuron blocker guanethidine and the non-selective alpha-adrenoceptor antagonist phentolamine did not affect the pain-related responses, although these agents suppressed the pain-related responses induced by partial ligation of the sciatic nerve. The pain-related responses induced by herpetic inoculation was suppressed by intraperitoneal and intrathecal injections, but not by intraplantar and intracerebroventricular injections, of clonidine. The suppressive effect of an intraperitoneal injection of clonidine (0.1 mg/kg) was antagonized by intrathecal injections of phentolamine and the alpha(2)-adrenoceptor antagonist yohimbine, but not the alpha(1)-adrenoceptor antagonist prazosin. The results suggest that sympathetic nerves and alpha-adrenoceptors are not involved in the pain-related responses induced by herpetic infection. Clonidine suppresses the responses probably through the action on alpha(2)-adrenoceptors in the dorsal horn.

Long-term outcomes during treatment of chronic pain with intrathecal clonidine or clonidine/opioid combinations

To evaluate the effectiveness of intrathecal clonidine or clonidine/opioid admixture for the treatment of chronic pain states, a retrospective chart audit of 15 patients seen by the Pain Medicine and Neurosurgical Services was performed. Subjects included 9 men and 6 women aged 26-86 years. Diagnoses included complex regional pain syndrome, neuropathic pain, and cancer pain. All patients received a trial of single-shot and/or short-term infusion of clonidine. Those reporting a significant reduction in pain, or at least 50% reduction in their visual analog scale (VAS), received long-term therapy. Intrathecal clonidine as a single-shot dose, infusion, or as intrathecal polytherapy did not improve VAS scales from pre-treatment values in 5 patients. Ten patients reported significant pain relief or >50% decrease in VAS scores with the initial trial and received long-term therapy. Two received clonidine alone for 7-11 months before the therapy failed; others failed after just a few days. Seven of eight initially responded to clonidine alone (75-950 microg/day) before failing and requiring a second drug. Three received hydromorphone (200-8000 microg/day) and four morphine (0.15-15 mg/day) with clonidine. Four patients then failed 2-drug therapy (duration 6-21 months). Two continue with intrathecal clonidine/hydromorphone (duration 19-29 months) and 1 with clonidine/morphine (duration 21 months). After initiation of intrathecal clonidine, one patient reported good relief with clonidine/morphine until his death 5 months later. In this population, intrathecal clonidine was of limited utility for most patients. It may be of benefit for subset(s) of patients, but in our experience, duration of relief is typically <18 months.

Identifying ambulatory cancer patients at risk of impaired capacity to consent to research

Ethicists and others have expressed concerns that some patients with cancer might lack adequate decision-making capacity to give consent for research. Although this concern is plausible, it is not known what patient characteristics might be used to identify those patients who are at risk and who therefore should undergo a formal assessment of decision-making capacity. Forty-five patients with cancer were presented with a description of a randomized controlled trial, accompanied by an Institutional Review Board-approved consent form. Two raters who were blind to all patient characteristics assessed decision-making capacity using the MacArthur Competency Assessment Tool for Clinical Research. These scores were summarized in overall capacity judgments using criteria established by a panel of experts. Subjects also completed a symptom rating scale and a battery of neuropsychiatric tests. No relationship was observed between symptom severity and any domain of decision-making capacity (understanding, appreciation, reasoning, ability to express a choice) or summary judgments. However, several other patient characteristics, including age, education, and selected neuropsychiatric test results, were found to be strongly associated with capacity scores. These data suggest that several patient characteristics, such as age, education, and tests of cognitive functions, may help investigators to identify patients with impaired capacity to give consent for research.

Management strategies for the treatment of neuropathic pain in the elderly

Pain caused by dysfunction or damage to the peripheral or central nervous system is typified by the symptoms described by patients with painful diabetic neuropathy, post-herpetic neuralgia and central poststroke pain. All these conditions are more common in the elderly. Neuropathic pain has long been recognised as one of the more difficult types of pain to treat; however, with the current emphasis on providing a multidisciplinary assessment and approach to management, more patients will be offered relief of their symptoms and an improved quality of life. Despite the use of combination drug therapy, adequate pain relief in the elderly is difficult to achieve without adverse effects. In an attempt to minimise these it is important to include non-drug treatment options in the management plan. Lifestyle changes and environmental modification, together with encouragement to adopt an appropriate exercise programme and an emphasis on maintaining mobility and independence should always be considered. Interventional therapy ranging from simple nerve blocks to intrathecal drug delivery can be of value. Drug treatment remains the mainstay of therapy. Tricyclic antidepressants such as amitriptyline, while having significant adverse effects in the elderly, have a number needed to treat (NNT) of 3.5 for 50% pain relief in diabetic neuropathy and 2.1 for 50% pain relief in postherpetic neuralgia. The newer antiepileptic drugs, such as gabapentin, appear to have a better adverse effect profile and provide similar efficacy with the NNT for treating painful diabetic neuropathy being 3.7 and 3.2 for treating pain in postherpetic neuralgia. As our understanding of the complexities of the pain processes increases, we are becoming more able to appropriately combine treatments to achieve not only improved pain relief but also improved function.

Intrathecal clonidine reduces hypersensitivity after nerve injury by a mechanism involving spinal m4 muscarinic receptors

alpha2-Adrenergic agonists reduce mechanical and thermal hypersensitivity in animals with nerve injury and effectively treat neuropathic pain in humans. Previous studies indicate a reliance of alpha2-adrenergic agonists in this setting on spinal cholinergic activation and stimulation of muscarinic receptors. The subtype(s) of muscarinic receptors in the spinal cord that produces antinociception in normal animals is controversial, and those involved in reducing hypersensitivity and interacting with alpha2-adrenergic systems after nerve injury are unstudied. To examine this, the left L5 and L6 spinal nerves were tightly ligated in rats, resulting in reduction in withdrawal threshold to punctate mechanical stimuli. Intrathecal clonidine, 15 micro g, returned the withdrawal threshold to normal. Using highly specific m1 and m4 antagonists, we observed no reduction in the effect of clonidine by the m1 antagonist, but inhibition of clonidine's effect by the m4 antagonist. Western analysis revealed no difference in quantitative expression of m1 and m4 receptor protein in the dorsal spinal cord of spinal nerve-injured animals compared with sham-operated controls, suggesting this interaction with m4 receptors does not reflect an increase in receptor expression.

IMPLICATIONS

Neuraxial clonidine is an effective adjunct in the treatment of neuropathic pain and increases acetylcholine concentrations in cerebrospinal fluid in humans. These data in animals suggest that spinal m4 type muscarinic receptors are important to the effect of clonidine in treating hypersensitivity to touch after nerve injury.

Chronic constriction injury of sciatic nerve induces the up-regulation of descending inhibitory noradrenergic innervation to the lumbar dorsal horn of mice

Peripheral nerve injury in rodents results in hypersensitivity to mechanical and thermal stimuli accompanied by reduced antinociceptive efficacy of opioids and, in some models, sensitivity to sympathetic blockade. alpha2-Adrenergic receptor agonists increase in potency and efficacy after nerve injury in rodents and effectively relieve neuropathic pain in humans who do not get pain relief from opioids. However, the underlying mechanisms are unclear. It has been well known that the major noradrenergic innervation of the spinal dorsal horn originates from the locus coeruleus nucleus (LC) in the brainstem. Therefore, the aim of this study is to examine whether peripheral nerve injury that causes neuropathic pain modulates the noradrenergic innervation to the lumbar dorsal horn, in order to determine the possible anatomical substrates underlying increased potency and efficacy of noradrenergic receptor agonists in alleviating neuropathic pain. At 2 weeks after chronic constriction injury (CCI) of the sciatic nerve, a remarkable increase in tyrosine-hydroxylase (TH) and dopamine beta-hydroxylase (DbetaH) immunoreactive (IR) axonal terminals was observed in the ipsilateral L4-L6 dorsal horn. Consistently, greater numbers of both TH- and DbetaH-IR neurons were detected in the ipsilateral LC. Interestingly, in the lower lumbar and upper sacral spinal dorsal horn, numerous TH-IR neurons were observed in the superficial dorsal horn (primarily lamina I). CCI of the sciatic nerve did not change the number of these TH-IR cells. These findings suggest that augmented descending inhibitory noradrenergic innervation to the dorsal horn could be one of the mechanisms underlying the increased effectiveness in the anti-allodynic effect elicited by alpha2-adrenergic receptor agonists.

Intrathecal clonidine added to a bupivacaine-morphine spinal anesthetic improves postoperative analgesia for total knee arthroplasty

Postoperative pain after total knee arthroplasty (TKA) is severe and can complicate early physical therapy. We tested the hypothesis that intrathecal clonidine would improve postoperative analgesia for TKA using a hyperbaric bupivacaine spinal anesthetic. In a double-blinded, placebo-controlled protocol, 81 ASA physical status I-III patients undergoing either a single or bilateral TKA were randomized into 4 groups with the following 2-mL solutions added to 15 mg of hyperbaric bupivacaine: 1) sterile saline, 2) morphine (250 microg), 3) morphine (250 microg) with clonidine (25 microg), and 4) morphine (250 microg) with clonidine (75 microg). At 1, 2, 4, 6, 12, and 24 h postoperatively, we measured visual analog scales (VAS), cumulative IV morphine consumption, hemodynamics, nausea, ancillary drugs, and side effects. Our primary comparison was between the clonidine with morphine groups versus the morphine group. We found that the combined administration of intrathecal clonidine and morphine decreased 24 h IV morphine consumption by 13 mg (P = 0.028) when compared with intrathecal morphine alone. This corresponded to a decrease in the VAS score of 1.3 cm at 24 h postoperatively (P = 0.047). Adverse side effects were similar among all groups with the exception of more relative hypotension in the clonidine groups through postoperative hour 6. We conclude that the coadministration of intrathecal clonidine and morphine decreases the 24-h IV morphine consumption and improves the 24-h VAS score when compared with intrathecal morphine alone.

IMPLICATIONS

In this prospective, randomized, double-blinded, and placebo-controlled trial, we identify an effective postoperative analgesic approach in total knee replacement surgery. Intrathecal morphine (250 microg) combined with clonidine (25 or 75 microg) provided superior analgesia compared with intrathecal morphine alone.

The effect of spinal bupivacaine in combination with either epidural clonidine and/or 0.5% bupivacaine administered at the incision site on postoperative outcome in patients undergoing lumbar laminectomy

Spinal anesthesia has numerous advantages over general anesthesia for patients undergoing lumbar laminectomy and microdisk surgery. In this study, we evaluated the addition of epidural clonidine and/or bupivacaine, injected at the incision site, on postoperative outcome variables in patients undergoing lower spine procedures using spinal anesthesia. One hundred twenty patients having lumbar spine surgery received bupivacaine spinal anesthesia supplemented by 150 microg of epidural clonidine with or without incisional bupivacaine, epidural placebo plus incisional bupivacaine, or placebo with incisional saline. Demographic data, intraoperative hemodynamics, blood loss, pain, nausea, urinary retention, hospital discharge, and other variables were compared by using either analysis of variance or chi(2) analysis. Demographics were similar. IV fluids, blood loss, incidence of intraoperative bradycardia, and hypotension were not different among groups. Postanesthesia care unit pain scores were lower and demand for analgesics was less in patients who received both the clonidine and subcutaneous bupivacaine. Patients who received epidural clonidine also had improved postoperative hemodynamics. Hospital discharge, urinary retention, and other variables were not different. We conclude that epidural clonidine as a supplement to spinal anesthesia produced no perioperative complications and improved postoperative pain and hemodynamic stability in patients undergoing lower spine procedures.

IMPLICATIONS

Spinal anesthesia with supplemental epidural clonidine in combination with incision site subcutaneous bupivacaine was evaluated both intra- and postoperatively and compared with spinal anesthesia alone for lower lumbar spine procedures. Both epidural clonidine and subcutaneous incisional bupivacaine, added to spinal anesthesia for lumbar spine surgery, improves pain relief and reduces the need for postoperative opioids with their associated side effects.

Continuous intrathecal clonidine and tizanidine in conscious dogs: analgesic and hemodynamic effects

Alpha-2-adrenergic agonists, such as clonidine, produce antinociception in animal pain models after intrathecal administration. However, clinical usage is limited by cardiovascular side effects. To investigate alternative alpha(2)-adrenergic agonists as analgesics, we implanted six dogs with an intrathecal catheter and infusion pump. After baseline saline infusion, animals received clonidine or tizanidine (crossover study) each week at escalating doses of 125-750 microg/h. Analgesia, blood pressure, heart rate, respiratory rate, sedation, and coordination were evaluated. A 28-day safety study was performed with another nine dogs receiving intrathecal tizanidine (3 or 6 mg/d) or saline. Equal doses of clonidine and tizanidine produce the same antinociception in thermal withdrawal tests. Blood pressure was reduced with 125-500 microg/h of clonidine, but not with tizanidine at any dose. Clonidine 250 microg/h reduced heart rate by 45.8%, and five of six animals had bradyarrhythmias (marked bradycardia), whereas tizanidine decreased heart rate by 15.1% without arrhythmias, even at the largest dose. Respiratory rate decreased with 250 microg/h of clonidine and larger doses. Sedation or incoordination occurred only at the largest dose for either drug. The safety study indicated that 3 mg/d of tizanidine in dogs produced no side effects or histopathologic changes. Tizanidine may be a useful alternative in patients experiencing cardiovascular side effects with intrathecal infusion of clonidine.

IMPLICATIONS

Clonidine is an effective spinal analgesic, but it is dose-limited by cardiovascular side effects. We compared the analgesic properties and side effects of clonidine with those of a similar drug, tizanidine. Continuous spinal infusion of tizanidine produced similar analgesia as clonidine, but with fewer adverse effects on blood pressure and heart rate.

Intrathecal ketorolac enhances antinociception from clonidine

Although both alpha2-adrenergic agonists and cyclooxygenase inhibitors produce analgesia, their exact sites of action and interaction remain unclear. A previous report demonstrated a surprising inhibition of antinociception in rats from intrathecal clonidine by co-administered ketorolac. There are no other reports of interaction between these two classes of analgesics. We therefore reexamined this interaction, determining the effect of intrathecal clonidine and ketorolac alone and in combination in normal rats. Clonidine, but not ketorolac, produced antinociception to noxious hind paw thermal stimulation. The addition of ketorolac significantly enhanced the effect of clonidine, indicating a synergistic interaction for analgesia. Although the reasons for the discrepancy between this and the previous report are unclear, these results are consistent with previous studies that indicate an antinociceptive action of intrathecal alpha2-adrenergic agonists in the normal condition, a lack of such effect for cyclooxygenase inhibitors, and positive reinforcing effects of these two systems when co-stimulated.

IMPLICATIONS

Spinal injection of the alpha2-adrenergic agonist clonidine and the cyclooxygenase inhibitor ketorolac results in a synergistic interaction for antinociception in normal animals, suggesting that the combination of these drugs will enhance rather than detract from the analgesia of either alone.

Epidural and intrathecal analgesia for cancer pain

The three-step analgesic ladder approach developed by the World Health Organization works well in treating the vast majority (70-90%) of patients suffering from pain related to cancer. In those patients who do not get pain relief by this three-step approach, intraspinal agents can be a fourth step in managing pain of malignant origin. Although morphine is the only opioid approved by the US Food and Drug Administration for intraspinal use, many different opioid analgesics are used intraspinally, including hydromorphone, fentanyl, sufentanil, meperidine and methadone in the treatment of cancer pain. Many non-opioid agents have also been used intraspinally either alone or in combination with opioids in the treatment of intractable cancer pain. This chapter summarizes the clinical use of these agents with some practical points.

The effect of chronic oral desipramine on capsaicin-induced allodynia and hyperalgesia: a double-blinded, placebo-controlled, crossover study

The tricyclic antidepressants are often used for the treatment of neuropathic pain. In this study, we evaluated one of these drugs on human cutaneous experimental pain. A randomized, double-blinded, placebo-controlled, crossover design methodology was conducted. Subjects participated in 2 14-day study sessions separated by a 7-day washout period. One session was with desipramine and one with placebo. At baseline, Day 7, and Day 15, quantitative sensory testing was performed to thermal and mechanical stimuli. On Day 15 only, intradermal capsaicin was injected on the volar aspect of the forearm followed by an assessment of pain and hyperalgesia. Oral desipramine had no significant effect on acute sensory thresholds, pain, secondary hyperalgesia, or flare response induced by intradermal capsaicin. Mean peak plasma levels of desipramine were within the therapeutic range for the treatment of depression. This study further supports a lack of effect of the tricyclic antidepressants on acute nociception and experimentally-induced secondary hyperalgesia.

IMPLICATIONS

Human experimental pain models have recently been developed; however, the efficacy of the tricyclic antidepressants (TCA) in these models has not been systematically studied. This investigation provides further validation of human experimental pain models and demonstrates that the chronic delivery of a TCA has no effect on human experimental pain.

Pain management services in palliative care: a national survey

INTRODUCTION

The effective management of pain requires a multidisciplinary approach. Previous studies have suggested that around 8% of cancer patients will require interventional techniques from an anaesthetist with special interest in pain management to maximize pain control, although this percentage may increase in the cohort of patients with difficult pain syndromes under the care of specialist palliative care services. We wished to determine the experiences and views of other palliative care physicians with regard to input from specialists in pain management.

METHOD

A postal questionnaire was sent to the consultant members of the Association of Palliative Medicine.

RESULTS

Most respondents had access to 'as-required' anaesthetist consultations with 72% of respondents feeling that the frequency of consultation was adequate. However, over half of the respondents had used the services of a pain management specialist less than four times in the past year and a quarter of respondents had not been involved in a joint consultation with an anaesthetist in the past year. All respondents felt that the pain management specialist's role included advice on technical procedures but less than 25% felt that their role should extend to advice on prescribing analgesics.

DISCUSSION

There are likely to be several reasons for this apparent underutilization of specialist anaesthetist/pain management services. This survey has identified possible factors including lack of formal arrangements, lack of suitable experience and the attitudes of palliative medicine consultants.

An investigation of monoamine receptors involved in antinociceptive effects of antidepressants

We attempted to determine which monoamine receptor subtypes are predominantly involved in antidepressant-induced antinociception. Antinociceptive effects were evaluated by using formalin tests with rats. Antidepressants acting as potent inhibitors of norepinephrine reuptake (nisoxetine, nortriptyline, and maprotiline) or inhibiting reuptake of both norepinephrine and serotonin (5-HT) (imipramine and milnacipran) induced dose-dependent antinociception. Simultaneous intraperitoneal administration of antidepressants and either prazosin (alpha(1) antagonist) or ketanserin (5-HT(2) antagonist) significantly antagonized antinociceptive effects. Fluvoxamine (selective serotonin reuptake inhibitor) induced antinociception less potently than other antidepressants and was significantly antagonized by ketanserin, but not prazosin. Ondansetron (5-HT(3) antagonist) significantly antagonized antinociception by 10 mg/kg of imipramine. In contrast, SDZ-205,557 (5-HT(4) antagonist) markedly enhanced antinociception by small-dose (2.5 mg/kg) imipramine. Imipramine-induced antinociception was significantly antagonized by intracerebroventricular administration of prazosin or ketanserin, but not by yohimbine (alpha(2) antagonist) or ondansetron, and was significantly enhanced by intracerebroventricularly administered SDZ-205,557. These findings suggest that alpha(1) adrenoceptors and 5-HT(2) receptors in the brain are involved in antidepressant-induced antinociception. In addition, the results suggested functional interactions between noradrenergic and serotonergic neurons as mechanisms for antidepressant-induced antinociception.

IMPLICATIONS

Formalin tests of rats treated with antidepressants and antagonists of monoamine receptors indicate that alpha(1) adrenoceptors, serotonin (5-HT)(2) receptors, and 5-HT(3) receptors are involved in antidepressant-induced antinociception, suggesting functional interactions between noradrenergic and serotonergic neurons as mechanisms of antidepressant-induced antinociception.

Effect of antisense knock-down of alpha(2a)- and alpha(2c)-adrenoceptors on the antinociceptive action of clonidine on trigeminal nociception in the rat

Although activation of alpha(2)-adrenoceptors is known to play an important role in mediating antinociception, the contribution of various alpha(2)-adrenoceptor subtypes in modulating trigeminal nociception remains unknown since subtype specific agonists and antagonists are not available. The present study investigated the functional role of alpha(2)-adrenoceptor subtypes in modulating the N-methyl-D-aspartate-induced nociceptive behavior in the medullary dorsal horn by using antisense oligodeoxynucleotides to selectively knock-down the receptor subtypes. Microinjection of N-methyl-D-aspartate (2 nmol in 10 microl) through a cannula implanted dorsal to the medullary dorsal horn produced a total of 164.9+/-8.8 scratches in the facial region (n=14), and the scratching behavior lasted for 77.8+/-5.2s (n=14). Microinjection of clonidine, an alpha(2)-agonist (7 microg in 5 microl), 15 min prior to administration of N-methyl-D-aspartate, produced a reduction of 71.6% (n=12) in the number of scratches and a reduction of 57.5% (n=12) in the duration. The inhibitory effect of clonidine was blocked by idazoxan (n=4) and yohimbine (n=4), alpha(2) antagonists. In rats pretreated with the antisense probe to the alpha(2A) adrenoceptor, clonidine only produced a reduction of 7.3% in the number of scratches (n=12) and a reduction of 9% in the duration (n=12). The antinociceptive effect of clonidine recovered completely 4 days after termination of the alpha(2A) antisense oligodeoxynucleotide treatment. In contrast to the alpha(2A) antisense-treated animals, clonidine reduced the number of scratches and the duration by 85.5% (n=9) and 82.1% (n=9), respectively, in rats pretreated with the sense probe to the alpha(2A) adrenoceptor. The effect of clonidine was not altered in rats pretreated with the antisense or the sense probes to the alpha(2C) adrenoceptor. In the alpha(2C) antisense pretreated rats, clonidine reduced the number of scratches and the duration by 60.8% (n=11) and 44.5 % (n=11), respectively. In the sense-pretreated rats, clonidine produced a reduction of 69.1% in the number of scratches (n=9) and a reduction of 55.1% in the duration (n=9). In order to assess the effectiveness of the antisense treatment, the receptor expression was examined by immunohistochemistry. Antisense treatment reduced alpha(2A) and alpha(2C) receptor immunoreactivity in the medullary dorsal horn compared to the sense and the vehicle-treated animals. Quantitative image analysis revealed a significant decrease in pixel intensity following the antisense treatment. These results indicate that activation of alpha(2A) adrenoceptor plays an important role in mediating the antinociceptive effect of clonidine in the medullary dorsal horn in the rat.

Are hospices ready to participate in palliative care research? Results of a national survey

BACKGROUND

Improvements in end-of-life care will require an active program of research, and this research will need to involve patients in hospice. However, it is not known whether hospices are prepared to participate in research, nor is it known what barriers may prevent hospices from becoming involved in research.

METHODS

This nationwide telephone survey was conducted with a random sample of hospice organizations taken from a national database. Questions elicited the research activities in which hospices are involved, the resources that hospices have available for the ethical review of research, and perceived barriers to research participation.

RESULTS

Of 88 hospices identified, 17 (19%) reported that they had participated in research in the past year. Hospices that participated in research were more likely to be urban, affiliated with an academic institution, and were more likely to have an inpatient unit. Hospices cited several barriers to research participation, including time commitments, staffing resources, ethical concerns, and burdens to patients and families. The most important concern was lack of staffing resources. Hospices indicated that they would be most willing to support research regarding pain management and timing of referral to hospice.

Advances in cancer pain management

Although most patients with cancer pain can attain a favorable balance between analgesia and side effects with a conventional approach to opioid therapy, a substantial minority cannot. For these patients, an important subgroup of whom have neuropathic pain, alternative therapeutic strategies are needed. With a detailed assessment, clinicians should be able to choose among the large and diverse group of options available and implement an approach, or combination of approaches, that have a high probability of improving analgesic outcomes.

Electrophysiologic characterization of the antinociceptive actions of S18616, a novel and potent alpha2-adrenoceptor agonist, after acute and persistent pain states

alpha (2)-Adrenoceptor (AR) agonists are active in behavioral models of persistent pain involving tissue and nerve damage. We evaluated the spinal effect of a novel, potent, and selective alpha (2)-AR agonist, [7,8](2-chlorobenzo)-2-amino-1-aza-3-oxa[4,5]spirodeca-1,7-diene (S18616), on the responses of dorsal horn neurons in halothane-anesthetized rats. Intrathecal administration of S18616 (0.1 to 3.0 microg) dose-dependently suppressed C- and A delta-fiber evoked responses but not the A beta-fiber evoked response. Drug effects were reversed by the alpha (2)-AR antagonists, atipamezole and idazoxan (100 microg). In rats with unilateral spinal nerve (L5-L6) ligation performed 2 weeks before study, S18616 (0.1 to 3.0 microg) dose-dependently suppressed the C- and A delta-fiber evoked responses and blocked "wind-up" in these neurons. The potency was comparable between nerve-injured and sham-operated rats, and S18616 was equally effective against responses to thermal and high-intensity mechanical stimuli. Interestingly, the effectiveness of S18616 on the low-intensity mechanical evoked response was significantly enhanced after nerve injury. Finally, S18616 (0.3 and 3.0 microg) reduced the neuronal responses produced by intraplantar injection of formalin. In conclusion, S18616 dose-dependently and potently inhibits the responses of dorsal horn neurons to peripheral stimulation in normal, inflamed, and neuropathic rats. These data support the use of spinal S18616 and other alpha (2)-AR agonists in the management of clinical pain.

Supportive therapy of elderly cancer patients

Elderly cancer patients often require supportive care due to the physiologic decline of organs and apparatus linked with the aging process per se, and for the effects of tumor or of anticancer treatments. Pain and nutritional deficits are some clinical aspects requiring supportive care. Lack of studies on these latter topics does not allow an in depth analysis of the problem. The present review deals with literature concerning pain and nutritional problems in the general cancer population with emphasis on aspects typical for elderly cancer subjects. Physiologic and cancer-related changes in body composition, physical function and cognitive capacity of the elderly are presented and, when appropriate, linked with pathogenetic factors of pain and malnutrition, as well as their treatment. Pain demographic data, pain intensity evaluation and currently available techniques to provide pain relief such as etiologic treatment, analgesic pharmacotherapy and invasive analgesic procedures, are extensively discussed. Causes and assessment of malnutrition as well as available nutritional approaches such as oral, enteral and parenteral nutrition are also debated.

Spinal noradrenergic activation mediates allodynia reduction from an allosteric adenosine modulator in a rat model of neuropathic pain

Activation of adenosine A1 receptors by endogenous adenosine or synthetic agonists produces anti-nociception in animal models of acute pain and also reduces hypersensitivity in models of inflammatory and nerve-injury pain. Allosteric adenosine modulators facilitate adenosine agonist binding to the A1 receptor. The purpose of the current study was to examine the effect, mechanisms of action, and interaction with noradrenergic systems of intrathecal (i.t.) or oral administration of the allosteric adenosine modulator T62 in a rat model of neuropathic pain. A spinal nerve ligation rat model (SNL; ligation of left L5 and L6 spinal nerve roots) was used. One week after SNL surgery, an i.t. catheter was inserted. Withdrawal threshold to mechanical stimulation of the left hind paw was determined before and after surgery, confirming mechanical hypersensitivity. Oral or i.t. T62 reduced hypersensitivity induced by SNL. The effects of i.t. T62 were inhibited by i.t. injection of an A1 receptor antagonist and by an 2-adrenergic antagonist but not by an A2 adenosine receptor antagonist. Anti-dopamine hydroxylase (DH)-saporin treatment reduce spinal norepinephrine content by 97%, accompanied by an almost complete loss of DH immunoreactive axons in the spinal dorsal horn and neurons in the locus coeruleus. The effect of T62 was completely lost in animals treated with anti-DH-saporin. These data support the hypothesis that activation of the A1 receptor by the allosteric modulator, T62, produces anti-nociception via spinal noradrenergic activation.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Spinal transection increases the potency of clonidine on the tail-flick and hindlimb flexion reflexes

The effect of intrathecal clonidine on thermal nociception and hindlimb flexion was assessed in acute and chronic spinally transected rats. After an acute, 1-day spinalization, there was no change in the antinociceptive dose-response function to clonidine, relative to intact rats. However, there was a significant increase in potency 31 days after spinalization. Low doses of clonidine (0.25, 1, 4 and 20 microg) did not affect the nonnociceptive flexion reflex of acute spinal rats, but they elicited a dose-dependent response in chronic spinal rats. These data provide behavioral evidence of supersensitivity to alpha-adrenoceptor agonists in chronic spinal rats.

Episodic (breakthrough) pain: consensus conference of an expert working group of the European Association for Palliative Care

BACKGROUND

Breakthrough pain is transitory exacerbation of pain that occurs in addition to otherwise stable persistent pain. The wide differences in estimation of incidence reported in literature are probably because of different settings and meanings attributed to the definition of breakthrough pain.

METHODS

A panel of experts met to establish the actual knowledge on breakthrough pain, according to the evidence in literature and experience. They agreed that episodic or transient pain could be a more simple and adequate term in most languages, including English, French, Italian, and Spanish.

RESULTS

A specific assessment and precise pain characterization are essential to plan the most appropriate treatments. Despite the relevance of this temporal pain pattern for the influence on the outcome and quality of life, few controlled studies have been performed to give evidence of a specific approach. Several experiences have reported the possible efficacy of different drugs, route of administration, and modalities of administration in different circumstances.

CONCLUSIONS

Prospective studies with previous treatments using similar terminologies are necessary to find the most convenient therapeutic intervention, according to the temporal pattern characteristics and the pain mechanism involved.

Strategies for the treatment of cancer pain in the new millennium

As was the case in the era before us, in the new millennium we will continue to see an abundance of patients experiencing cancer-related pain for different reasons. Although much needless pain and suffering still affects many of those with cancer, we are presented with a medical dichotomy. With the analgesic drugs available today, and the relatively simple and effective guidelines to treat cancer pain published and disseminated by the World Health Organization, why do people with cancer continue to experience pain? As we search for the answer, the horizon may hold promising new drugs, 'old drugs' with new interest and applications, and new strategies for the field of pain therapy. Possibilities include the isolation and development of analgesics or analgesic combinations that may minimise the adverse effects which are often associated with the current therapeutic class of opioid analgesics. In addition, current research points to promising results identifying the N-methyl D-aspartate non-opioid receptor as a likely component of neuropathic pain. Drugs such as gabapentin, the mechanism of action of which is not well known, have found favour within the clinical community for their analgesic properties and good tolerability. Methadone, in a phase of resurgence, has garnered the attention of the clinical community because of its unique receptor activity and pharmacoeconomic benefits. A number of clinical studies have demonstrated that methadone has a valuable role in treating cancer pain. Perhaps, an unbalanced focus on the risks of inappropriate use, rather than the benefits, should not compromise or distract from the use of methadone as an alternative to morphine. Studies are on going to assess the potential role of methadone in treating neuropathic pain. Drugs such as cannabinoids, although currently applicable for patients with anorexia, nausea and/or vomiting, may offer benefits to patients experiencing pain. Other opportunities exist with such compounds as alpha2-adrenergic agonists, nicotine, lidocaine and ketamine. New strategies such as the switching opioids and/or their route of administration may offer improved analgesia with fewer adverse effects, thus providing therapeutic alternatives for the clinical community. In addition, there is interest in the co-administration of opioids that act on different receptors. For instance, oxycodone appears to be a kappa opioid receptor agonist and may offer enhanced analgesia when combined with morphine.

Intrathecal Hydromorphone for Chronic Nonmalignant Pain: A Retrospective Study

OBJECTIVE

Ten percent to 15% of patients with chronic pain experience intolerable side effects or inadequate analgesia with continuous intrathecal morphine therapy. Although clinical experience suggests that rotation to hydromorphone (Dilaudid) can reduce side effects and recapture analgesia, there have been only scattered reports of long-term intrathecal hydromorphone use in patients with nonmalignant pain. The purpose of this study is to review the safety and effectiveness of continuous intrathecal hydromorphone in the management of patients with nonmalignant pain in whom continuous intrathecal morphine therapy has failed.

DESIGN

A retrospective review of 37 patients with chronic nonmalignant pain managed with intrathecal hydromorphone after failure of intraspinal morphine.

RESULTS

The mean age of patients was 64 years +/- 12 SD. All patients suffered from severe nonmalignant pain, most from failed lumbosacral spine operations (19/37; 51%). Morphine was replaced with hydromorphone because of pharmacological complications (21/37; 57%) or inadequate analgesic response (16/37; 43%) after an average of 11 months +/- 11 SD of intrathecal therapy. Pharmacological complications, particularly nausea and vomiting, pruritus, and sedation were reduced by hydromorphone in most patients. Peripheral edema was improved by hydromorphone but tended to recur with prolonged hydromorphone exposure. Analgesic response was improved by at least 25% in six of 16 patients who were switched to hydromorphone because of poor pain relief.

CONCLUSIONS

Hydromorphone can be a safe, analgesic alternative for long-term intrathecal management of nonmalignant pain among patients in whom morphine fails because of pharmacological side effects or inadequate pain relief.

The effect of maximal exercise on temporal summation of second pain (windup) in patients with fibromyalgia syndrome

Exercise activates endogenous opioid and adrenergic systems, but attenuation of experimental pain by exercise has not been shown consistently. In this study, effects of exercise on temporal summation of late pain responses to stimulation of unmyelinated (C) nociceptors were assessed. When a preheated thermode was applied repetitively to glabrous skin of the hand in a series of brief contacts at rates of 0.2 to 0.5 Hz, the perceived intensity of late thermal sensations increased after successive contacts. This summation of pain sensations provides information regarding the status of central opioid and N-methyl-D-aspartate receptor systems. For normal subjects, temporal summation of late pain sensations was substantially attenuated when testing began 1.5 or 10 minutes after exercise. Individuals diagnosed with fibromyalgia syndrome (FMS) report generalized chronic pain that is increased after exercise. Therefore, we hypothesized that strenuous exercise would increase summation of late pain sensations in this cohort. Patients with FMS and control subjects exerted to similarly high metabolic rates, as shown by physiologic monitoring. Ratings of late pain sensations increased for patients with FMS after exercise, an effect opposite to a decrease in ratings for age/sex-matched control subjects. In contrast to this result for experimentally induced pain, clinical pain ratings were not substantially altered after strenuous exercise by patients with FMS.

The Meissner corpuscle revised: a multiafferented mechanoreceptor with nociceptor immunochemical properties

Meissner corpuscles (MCs) in the glabrous skin of monkey digits have at least three types of innervation as revealed by immunofluorescence. The previously well known Aalphabeta-fiber terminals are closely intertwined with endings from peptidergic C-fibers. These intertwined endings are segregated into zones that alternate with zones containing a third type of ending supplied by nonpeptidergic C-fibers. Although MCs are widely regarded as low-threshold mechanoreceptors, all three types of innervation express immunochemical properties associated with nociception. The peptidergic C-fiber endings have readily detectable levels of immunoreactivity (IR) for calcitonin gene-related peptide (CGRP) and substance P (SP). The Aalphabeta endings have relatively lower levels of IR for CGRP and SP as well as the SP neurokinin 1 receptor and vanilloid-like receptor 1. Both the Aalphabeta and peptidergic C-fiber endings were also labeled with antibodies for different combinations of adrenergic, opioid, and purinergic receptors. The nonpeptidergic C-fiber endings express IR for vanilloid receptor 1, which has also been implicated in nociception. Thus, MCs are multiafferented receptor organs that may have nociceptive capabilities in addition to being low-threshold mechanoreceptors.