An unusual case of chronic neuropathic pain responds to an optimum frequency of intravenous ketamine infusions

The Potential Role of Ketamine in Hospice Analgesia: A Literature Review

OBJECTIVE

The objective of this review is to examine the role of ketamine as an analgesic for palliative treatment in the hospice care setting.

DATA SOURCES

The sources referenced in this review were found September 22, 2005, via an Internet search of the MEDLINE database and Cochrane Database of Systematic Reviews. Search terms included analgesia, cancer pain, dextromethorphan, hospice, ketamine, opioids, palliative care, neuropathic pain, and morphine. Articles and case reports were included that relate to ketamine use as an analgesic agent and not as an anesthetic.

DATA EXTRACTION

Because of patient variability with ketamine use and dosing, focus was placed on analgesic benefit versus no analgesic benefit. Because of the lack of controlled trials, application of all analgesic data related to ketamine use was relevant to this review. The strength of evidence is currently moderate, but the available trials and reports reviewed in this paper describe compelling results.

DATA SYNTHESIS

Ketamine has been effective in producing analgesia in patients receiving palliative care, especially when used in combination with opioids.

CONCLUSION

When opioid therapy is no longer sufficient to improve quality of life in the hospice setting, the addition of ketamine may be considered as adjunctive therapy.

Subanesthetic ketamine infusion therapy: a retrospective analysis of a novel therapeutic approach to complex regional pain syndrome

Complex Regional Pain Syndrome (CRPS) is a disorder that can be accompanied by severe pain that is often both chronic and resistant to conventional therapy. Harbut and Correll previously reported the successful treatment of a 9-year case of intractable Type I CRPS with an intravenous inpatient infusion of ketamine in an adult female patient.

OBJECTIVE

The purpose of this study was to ascertain if indeed the use of subanesthetic inpatient infusions of ketamine provide meaningful improvements in pain scores, and thus, quality of life, in patients suffering from CRPS. To achieve this objective we focused our analysis on the relief of pain obtained by patients undergoing this novel treatment option developed at Mackay Base Hospital, Queensland, Australia.

METHODS

Case notes of 33 patients whose CRPS pain was treated by the inpatient administration of a continuous subanesthetic intravenous infusion of ketamine were reviewed. The dose and duration of ketamine therapy and the degree and duration of relief obtained were recorded. Notable side effects were also recorded. The degree of relief obtained (immediately after the infusion) was assessed using pre- and posttreatment numeric pain scores. The duration of relief obtained (throughout the follow-up period) was analyzed using a Kaplan-Meier cumulative survival curve analysis.

RESULTS

A total of 33 patients with diagnoses of CRPS who had undergone ketamine treatment at least once were identified. Due to relapse, 12 of 33 patients received a second course of therapy, and two of 33 patients received a third. The degree of relief obtained following the initial course of therapy was impressive (N=33); there was complete pain relief in 25 (76%), partial relief in six (18%), and no relief in two (6%) patients. The degree of relief obtained following repeat therapy (N=12) appeared even better, as all 12 patients who received second courses of treatment experienced complete relief of their CRPS pain. The duration of relief was also impressive, as was the difference between the duration of relief obtained after the first and after the second courses of therapy. In this respect, following the first course of therapy, 54% of 33 individuals remained pain free for >/=3 months and 31% remained pain free for >/=6 months. After the second infusion, 58% of 12 patients experienced relief for >/=1 year, while almost 33% remained pain free for >3 years. The most frequent side effect observed in patients receiving this treatment was a feeling of inebriation. Hallucinations occurred in six patients. Less frequent side effects also included complaints of lightheadedness, dizziness, and nausea. In four patients, an alteration in hepatic enzyme profile was noted; the infusion was terminated and the abnormality resolved thereafter.

CONCLUSION

This retrospective review suggests that limited subanesthetic inpatient infusions of ketamine may offer a promising therapeutic option in the treatment of appropriately selected patients with intractable CRPS. More study is needed to further establish the safety and efficacy of this novel approach.

NMDA-mediated mechanisms in cortical excitability changes after limb amputation

OBJECTIVES

The aim of our study was to determine the role of N-methyl-d-aspartate (NMDA)-mediated mechanisms in cortical excitability changes after limb amputation, and their possible relationship to phantom pain.

MATERIALS AND METHODS

Sixteen upper limb amputees who were suffering from chronic phantom pain received the NMDA-antagonist memantine or placebo for 3 weeks. Intracortical inhibition (ICI) and intracortical facilitation (ICF) were determined at baseline and on day 21 using transcranial magnetic stimulation. Simultaneously, phantom pain intensity was assessed.

RESULTS

Memantine reduced ICF and enhanced ICI to roughly the same extent as seen in healthy subjects in a previous study. These changes were not correlated to the reduction of phantom pain.

CONCLUSION

We therefore conclude that NMDA-mediated mechanisms influence changes of ICI and ICF occurring after limb amputation. However, our results suggest that these cortical excitability changes and phantom pain are independent of each other.

Reflex sympathetic dystrophy

Reflex sympathetic dystrophy (RSD) is composed of five major features: pain, swelling, autonomic dysregulation, movement disorders, and atrophy and dystrophy. RSD is caused by an injury to a specific nerve or the C- and A-delta fibers that innervate the involved tissue. It is a progressive illness that spreads with time and may encompass the entire body. There is no psychological disposition to the problem, but all patients are severely depressed because of the constant pain, lack of sleep, and complete disruption of their lifestyle. The continuing pain is usually secondary to the process of central sensitization. The autonomic dysregulation has a major central nervous system component. Atrophy and dystrophy are partly due to loss of nutritive blood supply to the affected tissues. The movement disorder is partly due to deficiency of GABAergic mechanisms; the tremor is an exaggeration of the normal physiologic tremor. Treatment consists of decreasing the afferent pain, maintaining barrage from the underlying defect, and blocking the sympathetic component of the process. New developments include the use of neurotrophic factors to reverse the phenotypic changes that occur in the dorsal horn and the use of pharmacologic agents to block the activity-dependent NMDA channels that appear to be instrumental in maintaining central sensitization.