Publications by Year: 2008

2008

Lawrence J, Mackey SC. Role of neuroimaging in analgesic drug development. Drugs R. D. 2008;9(5):323-334.
Rapidly developing, non-invasive, neuroimaging methods provide increasingly detailed structural and functional information about the nervous system, helping advance our understanding of pain processing, chronic pain conditions and the mechanisms of analgesia. However, effective treatment for many chronic pain conditions remains a large, unmet medical need. Neuroimaging techniques may enhance our understanding of why currently available analgesics are ineffective for so many patients and aid in identifying new neural targets for pharmacological interventions of pain. This review examines how neuroimaging has enhanced our understanding of the mechanisms of chronic pain, the neural correlates of pharmacological modulation of pain, and the role of neuroimaging in analgesic development. Rather than focusing on one method, we discuss the advantages and limitations of several techniques that may each serve a unique role in aiding drug development, and we discuss current issues that exist in the design and implementation of pharmacological neuroimaging studies. Particularly, experimental design must be carefully considered as there are limitations in terms of the pharmacokinetics of the drug of interest as well as in respect to the capabilities of the neuroimaging method in use. Finally, we identify future directions including novel approaches that may also play a role in furthering our knowledge of the neural basis of analgesia. In the future, neuroimaging will certainly impact the methodology of analgesic drug development as it may lead to quicker and more efficient methods of evaluating the neural modulation of chronic pain.
Ochsner KN, Zaki J, Hanelin J, et al. Your pain or mine? Common and distinct neural systems supporting the perception of pain in self and other. Soc. Cogn. Affect. Neurosci. 2008;3(2):144-160.
Humans possess a remarkable capacity to understand the suffering of others. Cognitive neuroscience theories of empathy suggest that this capacity is supported by shared representations of self and other. Consistent with this notion, a number of studies have found that perceiving others in pain and experiencing pain oneself recruit overlapping neural systems. Perception of pain in each of these conditions, however, may also cause unique patterns of activation, that may reveal more about the processing steps involved in each type of pain. To address this issue, we examined neural activity while participants experienced heat pain and watched videos of other individuals experiencing injuries. Results demonstrated (i) that both tasks activated anterior cingulate cortex and anterior insula, consistent with prior work; (ii) whereas self-pain activated anterior and mid insula regions implicated in interoception and nociception, other pain activated frontal, premotor, parietal and amygdala regions implicated in emotional learning and processing social cues; and (iii) that levels of trait anxiety correlated with activity in rostral lateral prefrontal cortex during perception of other pain but not during self-pain. Taken together, these data support the hypothesis that perception of pain in self and other, while sharing some neural commonalities, differ in their recruitment of systems specifically associated with decoding and learning about internal or external cues.
Younger J, Barelka P, Carroll I, et al. Reduced cold pain tolerance in chronic pain patients following opioid detoxification. Pain Med. 2008;9(8):1158-1163.
OBJECTIVE: One potential consequence of chronic opioid analgesic administration is a paradoxical increase of pain sensitivity over time. Little scientific attention has been given to how cessation of opioid medication affects the hyperalgesic state. In this study, we examined the effects of opioid tapering on pain sensitivity in chronic pain patients. DESIGN: Twelve chronic pain patients on long-term opioid analgesic treatment were observed in a 7- to 14-day inpatient pain rehabilitation program, with cold pain tolerance assessed at admission and discharge. The majority of participants were completely withdrawn from their opioids during their stay. OUTCOME MEASURES: We hypothesized that those patients with the greatest reduction in daily opioid use would show the greatest increases in pain tolerance, as assessed by a cold pressor task. RESULTS: A linear regression revealed that the amount of opioid medication withdrawn was a significant predictor of pain tolerance changes, but not in the direction hypothesized. Greater opioid reduction was associated with decreased pain tolerance. This reduction of pain tolerance was not associated with opioid withdrawal symptoms or changes in general pain. CONCLUSIONS: These findings suggest that the withdrawal of opioids in a chronic pain sample leads to an acute increase in pain sensitivity.
Carroll IR, Kaplan KM, Mackey SC. Mexiletine therapy for chronic pain: survival analysis identifies factors predicting clinical success. J. Pain Symptom Manage. 2008;35(3):321-326.
Mexiletine, a sodium channel blocker, treats neuropathic pain but its clinical value has been questioned due to its significant side effects and limited efficacy. We hypothesized that ongoing therapy with mexiletine would have limited patient acceptance, but that an analgesic response to intravenous (IV) lidocaine (a pharmacologically similar drug) would identify patients most likely to choose ongoing therapy with mexiletine. We identified a cohort of 37 patients with neuropathic pain who underwent IV lidocaine infusions at our institution and were subsequently prescribed mexiletine. Time until discontinuation of mexiletine was used as the primary endpoint. Time until discontinuation is a clinically relevant, discrete, objective endpoint gaining acceptance as a metric for assessing clinical performance of drugs with significant side effects and limited efficacy. We used the techniques of survival analysis to determine factors that predicted continued therapy with mexiletine. Median time to discontinuation of mexiletine was only 43 days. A stronger analgesic response to IV lidocaine significantly predicted continued acceptance of mexiletine therapy. Decreasing age and male gender also predicted continued acceptance of mexiletine therapy. Analyzing time to mexiletine discontinuation uncovers important limitations in mexiletine s clinical performance missed by studies with conventional endpoints, such as change in pain score. Despite claims of efficacy, acceptance of mexiletine therapy is poor overall. Test infusions with lidocaine identify patients most likely to continue mexiletine therapy. Further work is needed to confirm these results and evaluate the relative acceptance of mexiletine vs. other treatments of neuropathic pain.