Predicting Chronic Pain After Peripheral Nerve Injuries

Pain is a funny thing. Two people can have the same injury and still experience pain completely differently. After some nerve injuries, there are individuals who just never fully recover. They have pain (referred to as chronic pain) the rest of their lives. Why is that? Why do some people recover just fine while others don’t?

These are questions researchers at the University of Toronto tried to answer in this study. They compared three groups of people: two groups had nerve injuries. One group was the normal, healthy control group for comparison.

Of the two groups with nerve injuries, the same nerves (median and/or ulnar nerves of the forearm and hand) were transected (cut across completely). After surgery to repair the damaged nerve, one of those groups recovered while the other group went on to develop chronic neuropathic (nerve-related) pain.

There are some theories about why some people have a poor recovery after nerve injury. Experts suspect personality, psychologic factors, and belief systems as the main reasons for impaired nerve regeneration. They name three specific individual factors addressed in this study: neuroticism, extraversion, and pain catastrophizing.

Let’s define each one. Neuroticism describes the way a person views his or her world. They experience most of life in a negative emotional state. They see even the ordinary day-to-day events as threatening. When it comes to pain, they focus on the sensation and see it as very disturbing until everything is blown way out of proportion.

Extraversion refers to a person who is outgoing, positive, active, and busy socially. An extravert is less likely to develop chronic pain than someone who is described as an introvert (shy, less outgoing, and more sensitive to things that might cause pain).

Pain catastrophizing means the person focuses more and more on the experience from a negative point-of-view. The person begins to fear moving as it might lead to pain or reinjury. The result can be disuse of the affected body part, disability, depression, and chronic pain.

How can these individual factors be identified in people? There’s a battery of physical and psychologic tests that can be given. Everyone in this study filled out numerous questionnaires about pain, activity, and hand function. They took a specific test called the Pain Catastrophizing Scale (PCS) designed to measure pain catastrophizing.

Physical tests of sensation (two-point discrimination, cold, vibration, texture) and nerve conduction were performed on each person. The researchers only included patients who had the nerve injury and surgery at least one-year ago. That gives the nerve time to recover and regenerate before testing its function. All test procedures used in this study were named, described, and discussed in detail.

What did they find? Is it really possible that personality and psychologic differences can account for why one person with a nerve injury heals and another one doesn’t? Actually yes — they did find that chronic pain following repair of peripheral nerves was linked with individual factors.

The patients with chronic pain were more likely to perceive stimuli (e.g., application of cold) as more unpleasant and more intense than the people in the group who had the same nerve injury and surgical repair but recovered.

The chronic pain group had more severe loss of nerve conduction (signals traveling along the nerve to the spinal cord and up to the brain). The results of the nerve conduction tests showed incomplete or inadequate recovery of nerves in the chronic pain group. They were less able to manipulate small objects with their fingers and more overall difficulty with movement (motor control).

How do these results relate to personality and pain catastrophizing? It seems the patients who had the worst results were more likely to focus on every aspect of their pain day and night. This behavior is referred to as pain vigilance. With pain vigilance comes the pain-related fear of movement already described.

People with neurotic tendencies scan their bodies over and over looking for signs of pain or disability. They focus on those symptoms and see them as threatening. Anxiety becomes a key feature in this cycle of vigilance-fear-avoidance-disability. Pain catastrophizing and neuroticism set the two pain groups apart.

The authors report that these findings are consistent with what other studies have shown. For example, previous studies looking at catastrophizing before surgery found that patients with a high degree of catastrophizing are less likely to recover fully after surgery. The catastrophizers are more likely to develop chronic pain.

This study adds to the knowledge we have about personality and beliefs as factors in health, healing, and recovery after peripheral nerve injury. Instead of thinking that incomplete nerve regeneration is the reason patients don’t recovery sensory-motor function, it is suspected that personality traits, pain beliefs, and coping strategies affect the healing process.

In summary, personality and psychologic testing may be able to predict who will recover after a peripheral nerve injury. On the flip side, these same tests may be able to point to patients who will have a poor recovery with chronic pain, loss of function, and long-term disability.