Pain and Motor Recovery May Share Same Pathway

Posted by Sam Maddox in Research News on December 17, 2016 # Research

Pain meds boost recovery? We reported in August on research into the possible dual role of anticonvulsant medications (e.g. Neurontin/gabapentin) commonly used to treat pain related to spinal cord injury. That blog noted this:

“... acute management of neuropathic pain may have beneficial effects over the first year post-injury. Specifically, individuals treated with anticonvulsants demonstrated greater recovery of muscle function compared with individuals not treated with anticonvulsants.”

Co-Principal Investigator for the pain/med paper was John Kramer, a scientist at the University of British Columbia, and a member of ICORD, the International Collaboration on Repair Discoveries. He has since published a report that in 225 individuals with SCI, 28 percent reported at- or below-level neuropathic pain. Those who got anticonvulsant medications at one month post injury “showed significant reductions in pain intensity and greater recovery in total motor scores.”

A related paper came out this week,Promoting Gait Recovery and Limiting Neuropathic Pain After Spinal Cord Injury: Two Sides of the Same Coin?” This is from a group in Quebec led by Laurent J. Bouyer at the Center for Interdisciplinary Research in Rehabilitation and Social Integration. Occupational therapist Catherine Mercier, lead author, speculates that both locomotor recovery and neuropathic pain are a result of adaptive plasticity of the spinal cord; indeed, pain and motor function may share the same mechanism, and therefore may interact with each other.

This research suggests that at the same time people with spinal cord injuries are being rehabbed with gait training, they are simultaneously beginning to develop nerve pain. Most studies of activity and training don’t mention pain. That ought to be studied, says Mercier.

... a better understanding of the interactions between pain and motor learning mechanisms could be used to promote or develop rehabilitation strategies that may lead simultaneously to better motor recovery and reduced chronic neuropathic pain.

Pain has long been seen as a secondary complication of injury; Mercier thinks it’s time to study pain as more than a symptom.

From the paper:

. . . a large proportion of patients will receive motor rehabilitation in the presence of pain. Surprisingly, very limited attention has been devoted to understanding the potential influence of pain on motor recovery, and in particular on gait retraining, during rehabilitation. Pain and motor recovery are typically considered as two independent problems in clinical research and practice, although both are ultimately recognized as having an impact on community reintegration and quality of life.

This gets a little complicated: pain may impede recovery, training can reduce pain. Animal studies show that pain can interfere with motor learning/recovery and, conversely, that early motor training might help preventing the development of neuropathic pain. Motor and pain are apparently on the same circuit.

On one hand, says Mercier, locomotor recovery is known to trigger adaptive plasticity and can lead to better walking recovery in incomplete injuries. On the other hand, pain can lead to what’s called central sensitization, which she defines as an amplified or hypersensitive pain signaling in the spinal cord: Central sensitization is considered as a form of maladaptive plasticity.

What does this mean? No one is really paying attention to the interactions between pain and motor learning. The paper tracked 93 studies of lower limb function related to training. Only two “hinted toward the inclusion of individuals with pain by reporting gabapentin use (a drug prescribed for neuropathic pain management) or having lost a patient at follow-up due to increased knee and low back pain.”

... there is only limited recognition of possible interactions between pain and motor learning/recovery in current rehabilitation research. As a result, clinical lower limb intervention studies have largely ignored or neglected pain after SCI, leading to internal and external validity problems. Unfortunately, this prevents an appropriate evaluation of the actual impact of the interaction between pain and motor learning on motor recovery after SCI.

To the best of our knowledge, the protective impact of motor training against the development of central sensitization that has been described in animal studies has not been addressed in the human acute pain model, despite a significant body of literature on the positive impact of exercise, including walking, in various chronic pain populations.

In conclusion, there is only limited recognition of possible interactions between pain and motor learning/recovery in current rehabilitation research. As a result, clinical lower limb intervention studies have largely ignored or neglected pain after SCI, leading to internal and external validity problems. Unfortunately, this prevents an appropriate evaluation of the actual impact of the interaction between pain and motor learning on motor recovery after SCI.

The Mercier paper suggests these steps:

Include patients with pain in locomotor studies to ensure external validity of the results;

Document pain adequately before, during, and after an intervention, to clarify any impact of pain on motor rehabilitation, and any impact of motor training on pain;

Consider neuromodulation strategies that could reduce the negative impact of pain on motor learning