Response to Sympathetic Block Predicts Response to Ketamine in Complex Regional Pain Syndrome

In patients with complex regional pain syndrome (CRPS), response to sympathetic nerve block may predict response to ketamine infusion, according to the results of a study published in Pain Medicine.

Patients (N=71) with CRPS who underwent a stellate ganglion or lumbar sympathetic nerve block followed by an infusion of ketamine at Johns Hopkins School of Medicine, Cleveland Clinic, or Seoul National University were included in this study. Clinical and demographic features and pain following sympathetic nerve block were compared with pain outcomes following ketamine infusion.

The mean age of the study population was 40.33±12.62 years, average duration of pain was 49.73±41.60 months, 84.51% of study participants had type 1 CRPS, more than half of the study participants reported having a comorbid psychiatric disorder, 54.93% used opioids, and mean baseline numeric rating scale (NRS) pain score was 7.08±1.79 points.

Lumbar sympathetic nerve block was performed in 91.55% of study participants, 61.97% received levobupivacaine, pain scores decreased by 54.73%±30.03% immediately following administration of the block, 57.75% maintained at least 50% pain relief for more than 3 hours, and 8.45% maintained at least 30% pain relief for at least 4 weeks.

A negative response to ketamine was reported by 38 patients, and a positive response was reported by 33. Among ketamine responders, NRS scores decreased from 7.24 to 3.64 points at the greater than 4-week follow-up.

There were no significant differences in demographic or clinical characteristics on the basis of ketamine outcomes. Patients who responded favorably to ketamine, however, had a higher rate of maintaining at least 50% pain relief for more than 3 hours (75.76% vs 41.11%; P =.009) and had a greater increase in temperature (mean, 5.66 °C vs 3.68 °C; P =.043) following administration of the nerve block.

Significant correlations were observed between percentage decrease in pain scores following ketamine infusion with temperature increase following sympathetic block (r, 0.41; P <.001) and percentage decrease in pain score at 4 weeks or longer after sympathetic block (r, 0.33; P =.005).

In the multivariate analysis, response to ketamine infusion was associated with obesity (odds ratio [OR], 8.75; 95% CI, 1.45-52.73; P =.018) and sympathetically maintained pain (OR, 6.54; 95% CI, 1.83-23.44; P =.004).

A major limitation of this study was the lack of standardization of postblock temperature and immediate pain relief assessments.

The authors of this study found that individuals who had a positive response to sympathetic nerve block for CRPS and patients who were obese were more likely to respond positively to ketamine infusion. The study authors comment, “In conjunction with other variables, the strategic use of sympathetic blocks in this population may be used as part of a personalized medical approach to individualize care and improve outcomes for more definitive therapies.” They caution that additional study is needed to identify patients for whom these treatment approaches would be appropriate.

This article originally appeared on Clinical Pain Advisor