Breakthrough pain characteristics and syndromes in patients with cancer pain. An international survey

Breakthrough pain (BKP) is a transitory flare of pain that occurs on a background of relatively well controlled baseline pain. Previous surveys have found that BKP is highly prevalent among patients with cancer pain and predicts more severe pain, pain-related distress and functional impairment, and relatively poor quality of life. An international group of investigators assembled by a task force of the International Association for the Study of Pain (IASP) evaluated the prevalence and characteristics of BKP as part of a prospective, cross-sectional survey of cancer pain. Fifty-eight clinicians in 24 countries evaluated a total of 1095 patients with cancer pain using patient-rated items from the Brief Pain Inventory (BPI) and observer-rated measures. The observer-rated information included demographic and tumor-related data, the occurrence of BKP, and responses on checklists of pain syndromes and pathophysiologies. The clinicians reported BKP in 64.8% of patients. Physicians from English-speaking countries were significantly more likely to report BKP than other physicians. BKP was associated with higher pain scores and functional interference on the BPI. Multivariate analysis showed an independent association of BKP with the presence of more than one pain, a vertebral pain syndrome, pain due to plexopathy, and English-speaking country. These data confirm the high prevalence of BKP, its association with more severe pain and functional impairment, and its relationship to specific cancer pain syndromes. Further studies are needed to characterize subtypes of BKP. The uneven distribution of BKP reporting across pain specialists from different countries suggests that more standardized methods for diagnosing BKP are needed.

Superior hypogastric plexus block successfully treats severe penile pain after transurethral resection of the prostate

BACKGROUND AND OBJECTIVES

Superior hypogastric plexus block has been used to treat cancer pain of the pelvis.

METHODS

A patient with severe chronic nonmalignant penile pain after transurethral resection of the prostate underwent a single superior hypogastric plexus block with local anesthetic and steroid. The patient was also started on medications that treat neuropathic pain a few hours after the procedure was finished.

RESULTS

The superior hypogastric plexus block resulted in complete pain relief immediately after the procedure. The pain relief continued at 1, 2, 4, and 8 months follow up.

CONCLUSIONS

In this case of severe penile pain the superior hypogastric plexus block was useful diagnostically and therapeutically.

Therapeutic drugs for neuropathic pain

Neuropathic pain is common and may be resistant to usual doses of analgesic medications. However, an improved understanding of the pathophysiology of neuropathic pain and a growing number of adjuvant medications that are useful for the treatment of neuropathic pain provide renewed hope for clinicians and their patients. It is useful to classify adjuvant analgesic drugs into two broad categories. Membrane stabilizing agents, which include the anticonvulsants, antiarrhythmics and probably corticosteroids, may act by blocking sodium channels on damaged neural membranes. Medications that enhance dorsal horn inhibition, which include the antidepressants and some anticonvulsants, may augment biogenic amine or GABAergic mechanisms in the dorsal horn of the spinal cord. Current evidence regarding efficacy generally does not support the use of one agent over another and selection of a particular agent may depend in part on the expected side effects or experience with a given drug. For maximum analgesic effect, more than one agent may be necessary and to improve therapy and minimize side effects, medications generally should be started at lower doses and titrated slowly to effect. Although labor-intensive, this strategy may improve compliance and optimize patient care.

Deafferentation pain exacerbated by subarachnoid lidocaine and relieved by subarachnoid morphine. Case report

BACKGROUND AND OBJECTIVES

Neuropathic pain syndromes are often resistant to traditional pharmacologic treatment. The authors describe a patient with chronic deafferentation pain of the legs associated with peripheral neuropathy that was refractory to multidisciplinary pain clinic management.

METHODS

Numerous medications had been tried, including nortriptyline, mexiletine, and oral and parenteral opioids. Spinal cord stimulation was also ineffective, despite a satisfactory pattern of stimulation-induced paresthesias. For diagnostic purposes, differential spinal anesthesia with lidocaine and morphine was performed, with evoked potential monitoring used to evaluate the intensity of spinal anesthetic block.

RESULTS

Paradoxically, lidocaine spinal anesthesia exacerbated pain, whereas subarachnoid morphine provided rapid pain relief. Long-term pain control has been maintained with an implanted spinal infusion pump.

CONCLUSIONS

Evoked potential data acquired during lidocaine spinal anesthesia and the rapid pain relief provided by subarachnoid morphine suggest that deafferentation pain may involve segmental, opioid-sensitive dorsal horn pain generators. The long-term pain relief afforded the patient demonstrates that subarachnoid opioids may be efficacious for some forms of neuropathic pain.

Dorsal nerve block for management of intraoperative penile erection

Intraoperative penile erection during general anesthesia can delay or prevent the completion of cystoscopic or penile surgical procedures. The dorsal penile nerve block is offered as a treatment for intraoperative erection. Advantages of this technique include less potential for cardiovascular complications and improved postoperative analgesia.

Dorsal root entry zone stimulation for deafferentation pain

Dorsal root entry zone (DREZ) stimulation was performed in 12 patients with chronic pain syndromes after extensive trials of medical therapy, sympathectomy or peripheral nerve stimulation had failed, with 50% of them obtaining excellent long-term benefit. Evoked potential monitoring to facilitate positioning of electrodes under either general or spinal anesthesia, and postoperatively to explore the mechanism of action, revealed findings distinct from those reported with conventional spinal cord stimulation (SCS). DREZ stimulation may function on a different neurophysiologic basis than conventional SCS, involving intersegmental processing and influencing tract of Lissauer functions or the dorsal horn directly.

Sites of action of subarachnoid lidocaine and tetracaine: observations with evoked potential monitoring during spinal cord stimulator implantation

BACKGROUND

The precise sites of action of local anesthetics on the spinal cord remain speculative. Monitoring spinal cord conduction during spinal anesthesia may provide a more precise localization of anesthetic action.

METHODS

Fifteen patients admitted for elective surgical implantation of spinal cord stimulators for treatment of chronic pain participated in the study. Lidocaine (mean dose, 90 mg) was used in 14 patients; one patient received 7.5 mg tetracaine. To assess spinal cord conduction, paresthesias elicited by spinal cord stimulation were monitored during onset and maintenance of spinal anesthesia. In eight patients, evoked potential monitoring was used to further assess cord conduction.

RESULTS

Despite complete motor block of the lower extremities and sensory levels to upper thoracic dermatomes (T1-8), all patients felt trial stimulator-induced paresthesias during spinal anesthesia. In addition, cortical evoked potentials from cord stimulation were maintained during spinal anesthesia. However, attenuation of cortical evoked potential amplitudes and paresthesias occurred, which were restored by increasing stimulus intensity. In contrast, even at maximum stimulus intensity, paresthesias and somatosensory evoked potentials from tibial nerve stimulation were abolished during spinal anesthesia.

CONCLUSION

Based on these observations, the predominant site of action of subarachnoid lidocaine and tetracaine appeared to be at spinal rootlets, although partial block of afferent cord conduction also occurred.

Interaction of GABA and volatile anesthetics in the nematode Caenorhabditis elegans

The authors tested whether mutant strains of Caenorhabditis elegans with altered sensitivity to volatile anesthetics have altered responses to GABA or GABA-agonists. They determined the ED50s of the wild-type strain N2 and two mutant strains of C. elegans to a GABA-mimetic ivermectin (IVM) and to GABA. unc-79, a strain with increased sensitivity to halothane, was more sensitive than N2 to IVM and GABA. unc-9, a strain that suppresses the increased sensitivity of unc-79 to halothane, was less sensitive than N2 to IVM and GABA. The authors also tested whether doses of GABA or IVM and volatile anesthetics were additive in their effects on C. elegans. Halothane (2.1%) did not shift the ED50 of IVM, but was antagonistic to GABA. Enflurane (4%) was antagonistic to both IVM and GABA. However, ED50s of halothane and enflurane were unchanged in the presence of IVM (35 nM) or GABA (150 mM). The authors conclude that GABA by itself does not appear to mediate halothane or enflurane sensitivity in C. elegans.