Nerve blocks and cognitive therapy : A beneficial failure

The trial by Gale et al (pages 185-189) is a valuable example of a negative result - the sort of finding that is published less often than a positive one. But, we can learn from the failure, both in understanding correct treatment and in planning future trials. Patients were recruited in a clinic where repeated treatment by nerve blocks is used as a palliative measure for chronic pain of all types. They were then offered the choice of entering a group with cognitive behavioural therapy or continuing with nerve blocks. For ethical reasons, patients could freely leave either branch of the trial without prejudice. At the onset, one of 34 patients in the nerve-block group left, while 12 departed from the cognitive therapy group. All 33 patients remaining in the nerve block group completed the eight-week trial, while only four of 34 patients completed it in the cognitive therapy group.

T he trial by Gale et al (pages 185-189) is a valuable example of a negative result -the sort of finding that is published less often than a positive one.But, we can learn from the failure, both in understanding correct treatment and in planning future trials.Patients were recruited in a clinic where repeated treatment by nerve blocks is used as a palliative measure for chronic pain of all types.They were then offered the choice of entering a group with cognitive behavioural therapy or continuing with nerve blocks.For ethical reasons, patients could freely leave either branch of the trial without prejudice.At the onset, one of 34 patients in the nerve-block group left, while 12 departed from the cognitive therapy group.All 33 patients remaining in the nerve block group completed the eight-week trial, while only four of 34 patients completed it in the cognitive therapy group.
Three conclusions followed.Too few patients remained in the cognitive therapy group to permit an intergroup comparison of efficacy.Those who conduct any future trial should beware of using patients who have established an existing preference; and there may be a small subgroup that will respond to cognitive behavioural therapy and should be recognized, treated and identified if possible for further attention.
Meanwhile, nerve-block treatment continues to present a conundrum.Patients benefit for longer periods of time than the duration of the anesthetic used.This phenomenon has been documented in the literature, and is regularly observed by clinicians, particularly those with an anesthesia background.Arner et al (1) reported that two-thirds of 38 patients with neuralgic pain experienced up to six days of relief from local anesthetic blocks of the affected nerve.But despite evidence that the practice of local anesthetic blocks for chronic pain is widespread, few trials have been published.While the current study may have certain limitations, it is necessary to continue this line of work.
The mechanisms by which local anesthetics abolish chronic pain for several days when they are effective for a maximum of 4 h if used for acute or 'physiological' pain, are not known.Several theories have been suggested.In an essay on the future of local anesthetics, Wall (2) lists several.The sympathetic nervous system has been implicated (3) and in a series of articles in Pain Reviews, McCormack (4,5) speculated that such blocks cause temporary abolition of spontaneous ectopic discharges, resulting in abolition of dynamically maintained central hyperexcitability, as well as reinforcing endogenous G-protein-coupled receptor inhibition of n-type voltage-sensitive calcium channels.Finally, the new data on glial activation in pathological pain (6) may cast doubt on the utility of cognitive behavioural therapy and other psychological interventions, while lending new legitimacy to local anesthetic block procedures, Nerve blocks and cognitive therapy: A beneficial failure explaining the findings in the Gale et al (pages 185-189) study.The work of Linda Watkins et al (6) shows that spinal cord glia can be activated in response to a variety of stimuli, both tissue injury and infections, bacterial and viral.The activated glia produce a number of proinflammatory cytokines associated with central sensitization.This activation spreads from cell to cell across 'gap junctions', following no particular neuronal pathways or anatomical boundaries.
Up to the present, such pain has been termed 'medically unexplained' (formerly 'psychogenic, 'somatizing' or even 'hysterical').It was thought that maladaptive psychological processes were primarily responsible for causing regional pain, and it was therefore assumed that psychological interventions might be the most logical treatment modality.It now seems highly likely that 'unexplained' regional pain is the result of organic or neurochemical changes; therefore, they are 'medically explained'.Hence, therapeutic modalities that can, even temporarily, reduce neuronal excitability and sympathetic nervous system malfunction may result in just the sort of benefits from local anesthetic blocks documented by Gale et al (pages 185-189).The time is ripe for renewed interest in nerve block models for the relief of pain.Those models are the ultimate foundation of the truly multidisciplinary pain clinic, and their results encouraged pioneers such as Bonica (7) and Travell (8) in taking chronic pain seriously.A look at their work may help to renew some well-established approaches that are currently neglected or out of favour.

Pain Res Manage Vol 7 No 4 Winter 2002 176
The views expressed in this editorial are those of the authors and are not intended to reflect the opinions of the Canadian Pain Society or Pulsus Group Inc L 'étude réalisée par Gale et coll. (pages 185 à 189) est un exemple utile d'étude non concluante.Contrairement à ceux des études probantes, les résultats d'un échec ne sont guère publiés.Pourtant, on peut aussi en tirer des leçons pour la planification d'études et les traitements.