Exaggerated pain responses are a common finding in chronic whiplash. Evidence is beginning to accumulate from animal and healthy human volunteer studies on the role of the central nervous system in chronic pain states following a whiplash injury.
Prolonged input of painful impulses from injured tissues leads to changes in the spinal cord and brain. At the spinal cord level, there is an increase in excitability of nerve cells. This is illustrated by the following picture that shows the pain referral patterns with injection of saline into one of the leg muscles. As can be seen from the figure below, the area and intensity of pain in whiplash patients is much more compared to normal controls.
Spinal cord excitability is normally modulated by a balance of excitatory and inhibitory inputs from the brain. Higher brain centres could activate receptors in the spinal cord leading to hyperexcitability at the spinal cord level. These excitatory pathways could be driven by fear and anxiety which are common in chronic pain patients. The role of central sensitisation in chronic pain states is illustrated by the following diagram.
Measuring Central sensitisation clinically: In chronic WAD, sensitivity to manual palpation could be found as distant as the leg. In our clinic, we often resort to a pressure algometer to detect pain thresholds. However, simple manual palpation of structures that are distant from the injured tissues is still a good test of central sensitivity. Also, sensitivity to cold has been found to be a marker of central sensitisation.
Preventing and Treating Hypersensitivity: Early identification and intervention is key to preventing and treating hypersensitivity in Whiplash. Those patients with a history of repeated neck trauma, fibromyalgia, depression and anxiety are at a higher risk of developing central sensitisation. Therapeutic options can be physical, pharmaceutical and psychological. From a physical therapy perspective, graded exercises and dry needling in the form of Acupuncture or Intramuscular stimulation are effective interventions. Pharmacologic interventions that have been suggested in literature include opioids, antidepressants and COX-2 inhibitors. Zygapophyseal joint injections are a validated treatment option in cases where a specific locus of nociception can be identified.
Hypersensitivity in whiplash is a challenge to clinicians of all hues. At Acadia Physical Therapy, we strive to identify patients who are at risk of developing chronicity so that interventions can be tailored to the individual. It is our goal to work with community physicians to prevent chronicity and facilitate the recovery process where chronicity is underway.