Abstract: We included an additional four studies (N = 154) in this update. For this update, we excluded studies that did not follow up patients for more than 48 hours. As a result, we excluded four studies from the previous review in this update. Overall we included 12 studies (N = 461), all of which we judged to be at high or unclear risk of bias. Overall, the quality of evidence was low to very low, downgraded due to limitations, inconsistency, imprecision, indirectness, or a combination of these. Two small studies compared LASB to placebo/sham (N = 32). They did not demonstrate significant short-term benefit for LASB for pain intensity (moderate quality evidence). One small study (N = 36) at high risk of bias compared thoracic sympathetic block with corticosteroid and local anaesthetic versus injection of the same agents into the subcutaneous space, reporting statistically significant and clinically important differences in pain intensity at one-year follow-up but not at short term follow-up (very low quality evidence). Of two studies that investigated LASB as an addition to rehabilitation treatment, the only study that reported pain outcomes demonstrated no additional benefit from LASB (very low quality evidence). Eight small randomised studies compared sympathetic blockade to various other active interventions. Most studies found no difference in pain outcomes between sympathetic block versus other active treatments (low to very low quality evidence). One small study compared ultrasound-guided LASB with non-guided LASB and found no clinically important difference in pain outcomes (very low quality evidence). Six studies reported adverse events, all with minor effects reported. This update's results are similar to the previous versions of this systematic review, and the main conclusions are unchanged. There remains a scarcity of published evidence and a lack of high quality evidence to support or refute the use of local anaesthetic sympathetic blockade for CRPS. From the existing evidence, it is not possible to draw firm conclusions regarding the efficacy or safety of this intervention, but the limited data available do not suggest that LASB is effective for reducing pain in CRPS.

Plain-language summary: In September 2015, we found a limited number of small trials, all of which had design flaws. We did not find evidence that LASB was better than placebo in reducing pain, or that it provided additional pain relief when added to rehabilitation. While a number of small studies compared LASB to other treatments, most did not find that LASB was better. One small study found that injecting the thoracic (upper back) sympathetic nerves with local anaesthetic and steroid was better than injecting the same drugs just under the skin at one-year follow-up, but the study may have been prone to bias. Only six studies reported on the type and amount of side effects. These studies reported only minor side effects, but since some studies did not report this information we can draw no firm conclusions about the safety of LASB. The evidence was mostly of low or very low quality. Overall, the evidence is limited, conflicting, and of low quality. While we cannot draw strong conclusions, the existing evidence is not encouraging.