Based largely on his clinical experience, the founding father of modern pain medicine, John J. Bonica, recommended that complex regional pain syndrome (CRPS) be treated with a series of sympathetic blocks as soon as possible after symptoms develop. Although this sometimes seems to work well, the value of this approach has been questioned because of the failure in randomised double-blind placebo-controlled trials to verify consistent treatment benefits. There could be good reasons for this – for example, some of the placebo-controlled trials had small samples, possibly too small to identify positive responses in a subgroup of responsive patients; sympathetic blocks might alleviate only part of the problem in CRPS; or placebo procedures might produce powerful treatment effects, at least temporarily, that conceal benefits of sympathetic blockade. Alternatively, sympathetic blocks might simply be ineffective.
Some of these issues were addressed recently in a study by de Oliveira Rocha and colleagues (2014). They selected participants with CRPS type I whose pain had failed to respond adequately to standard rehabilitation or drug treatments. The participants received a single thoracic sympathetic block (injection of 10 mL local anaesthetic and corticosteroid solution into the thoracic sympathetic chain) or a control procedure (injection of the same drugs under the skin in the thoracic region of the back). The participants were then treated with physiotherapy and analgesic medication over the next 12 months.
Remarkably, benefits of sympathetic blockade on pain and depressed mood were detected not only at one month but also 12 months later. In particular, scores on the McGill Pain Inventory were lower in the sympathetic block than control group at both time points, and at 12 months depression scores on the Hospital Anxiety and Depression Scale were 9% lower in the sympathetic block group than in controls. Average pain intensity was similar in both groups at one month, but was significantly lower at 12 months in patients who had received the sympathetic block than in controls. Effect sizes might have been inflated by small group sizes (19 in the control group and 17 who received sympathetic blockade). Nevertheless, the consistency of effects across multiple measures and time points suggests that the intervention was effective. Why the sympathetic block worked so well is a mystery, but perhaps an anti-inflammatory effect of local anaesthetic agents and corticosteroids around the sympathetic chain or dorsal root ganglia inhibited pain enough for participants to benefit from analgesic medications and to engage more fully in physiotherapy.
Animal studies provide convincing evidence that the sympathetic nervous system is involved in certain forms of chronic pain. De Oliveira Rocha’s findings strengthen the case that the sympathetic nervous system contributes to CRPS type I in humans. Obviously more research is needed to identify the optimal treatment parameters (e.g., the number of sympathetic blocks; the best time to administer them; the volume and contents of the injected solution; who is likely to benefit most from sympathetic blockade; components of post-block rehabilitation). However, De Oliveira Rocha’s findings already offer some hope for people having to deal with a remorseless, intractable condition.
About Peter Drummond
Professor Peter Drummond is a clinical psychologist and Professor of Psychology at Murdoch University, where he has worked since 1987. He has worked closely for many years with neurologists and pain specialists to investigate headache mechanisms and the physiological basis of complex regional pain syndrome. The focus of his more recent studies has been to clarify mechanisms of interaction between the sensory and sympathetic nervous system both in normal circumstances and after tissue injury and inflammation.
Reference
de Oliveira Rocha R, Teixeira MJ, Yeng LT, Cantara MG, Faria VG, Liggieri V, Loduca A, Müller BM, Souza AC, & de Andrade DC (2014). Thoracic sympathetic block for the treatment of complex regional pain syndrome type I: a double-blind randomized controlled study. Pain, 155 (11), 2274-81 PMID: 25149143