Ketamine infusion provide relief for patients with complex regional pain syndrome (CRPS).
While a successful infusion series is defined as a greater than 30% decrease in overall pain, immediate relief from pain usually range from 53% to 84%. At 1 to 3 month follow up, many still have a 41% to 75% reduction in pain from baseline. For most, pain relief last for 1 to 3 months in length before a maintenance infusion dose is needed.
While a recent metanalysis cause for the need for more studies for short term pain relief in CRPS, the current data is hard to ignore.
What is complex regional pain syndrome?
Complex regional pain syndrome (CRPS) is a chronic (lasting greater than six months) pain condition that most often affects one limb (arm, leg, hand, or foot) usually after an injury. CRPS is believed to be caused by damage to, or malfunction of, the peripheral and central nervous systems. The central nervous system is composed of the brain and spinal cord; the peripheral nervous system involves nerve signaling from the brain and spinal cord to the rest of the body. CRPS is characterized by prolonged or excessive pain and changes in skin color, temperature, and/or swelling in the affected area.
CRPS is divided into two types: CRPS-I and CRPS-II. Individuals without a confirmed nerve injury are classified as having CRPS-I (previously known as reflex sympathetic dystrophy syndrome). CRPS-II (previously known as causalgia) is when there is an associated, confirmed nerve injury. As some research has identified evidence of nerve injury in CRPS-I, it is unclear if this disorders will always be divided into two types. Nonetheless, the treatment is similar.
CRPS symptoms vary in severity and duration, although some cases are mild and eventually go away. In more severe cases, individuals may not recover and may have long-term disability.
In a recent meta-analysis published in Current Pain and Headache Reports. 2 investigators reviewed independently published randomized controlled trials and cohort studies that assessed intravenous infusion of the N-methyl-D-aspartate receptor antagonist ketamine for the treatment of CRPS.
In included studies, the primary outcome was pain relief, evaluated before and after treatment using the visual analog scale.
The pain relief event rate, defined as the percentage of patients achieving ≥30% pain relief was the secondary outcome. Overall, 15 studies with a total of 258 participants with CRPS were included in the final analysis (mean age, 37.34±9.23 years; mean CRPS duration, 39.67±31.61 months; mean duration of ketamine infusion, 8.41 days). Ketamine concentrations varied highly across studies. Ketamine infusion was found to be associated with a decrease in the average pain score at follow-up when compared with baseline (P <.000001). Immediate pain relief event rate was 69% (n=9 studies; 95% CI, 53%-84%) and pain relief event rate at follow-up ranging from 1 to 3 months was 58% (95% CI, 41%-75%).
The investigators note the current analysis contains a significant level of between-study heterogeneity as well as publication bias. In addition, the findings from this study are limited to a period of 3 months posttreatment onset, and this meta-analysis cannot determine conclusively whether the effects observed with the ketamine treatment are the result of placebo effect, as only one study included in the analysis included a placebo group.
”Our study suggested that ketamine infusion can provide clinically effective pain relief in short term for less than 3 months,” concluded the study authors.
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