WHAT IS CHRONIC PAIN?

Thousands of Danes live with muscle- and joint pain every day. Pain is defined as: “An unpleasant sensory- and emotional experience associated with actual or potential tissue damage” (IASP). Put differently: Pain is simply the body, warning us about potential or acute dangers, such as a burning hot stove touching our skin. Pain is something we all experience. How intensively we experience pain impulses is individual, and only you can assess the intensity of your pain.

Pain can be regarded as acute or chronic pain. Acute pains are, typically, short-termed and are the result of sudden tissue damage to bones, muscle- or organs, e.g., when a nail pierces your hand. Chronic pain is defined as pain which has lasted more than three months. Chronic pain may follow a case of acute tissue damage, but chronic pain may also occur in connection with, e.g., cancer, functional- and mental illness. Pain may manifest in many different forms and to gain further insight into the development of chronic pain, we first must define the process behind pain.

Our nervous system can be compared to any other electric circuit, where sensors in the periphery constantly rapport back to an electric component, in this case: “the brain”. When we experience pain, the nerve cells, which deal with pain, are activated. The neuron cells pass the signal on to the spinal cord, which transmits the signal to the brain.

Tissues around your body is scattered by nerves that solely react to pain. These nerve cells are known as nociceptors. Nociceptors send information both ways from the periphery nervous system to the spinal cord. To transmit their signals to another . the nociceptor synthesizes different molecules. Unfortunately, the same molecules may sensitize the nociceptor, reducing its threshold against painful stimuli.

At first, the nervous system will activate motoric functions, to ensure no further tissue damage (in this case, we move our hand away from the burning stove). The body will start an inflammation process, meaning the blood vessels around the wound expanses, which allows beneficial chemicals to aid the immune system in tissuse healing. In the inflammation process, the nerves are sensitized, effectively amplifing the pain signals. This is called neurogenic inflammation, and this is a part of the accute pain process. This reaction takes place in the periphery nervous system, e.g., our skin and limbs, and this process is a key factor in the development of chronic pain.

Why some people develop chronic pain and others do not, we simply do not know for sure. Research suggests, however, that a sensitization process occurs in three different stages of the nervous system: the periphery-, the central nervous system (the spinal cord), and in the brain. A sensitization means the system becomes overly sensitive towards pain impulses.

Only when the signal reaches a core area of the brain known as thalamus, does the brain begin to interpret the signal. Thalamus works as a kind of switch which transmits the signal to the relevant parts of the brain, where the information is processed. Within the brain, we find the so-called somatosensory center, which is associated with sensation – including pain impulses.
We know when pain occur in one place on the body (e.g., the right side) is processed in the opposite side of the brain (in this case the left). This matters to the way we view chronic pain-patients, because when we know the bodily location of the pain, we can specify the exact part of the patient’s brain, where the pain is processed. Therefore, it would be benificial to focus solely on this specific area, which ensures the best result.

When painful signals reach the brain, it will, under non-chronic circumstances, try to reduce these signals. The brain does this by emitting morphine-like molecules to the spinal cord, to ease the pain. The signal transmission between the nociceptors and the nerve cells in the spinal cord, is simply blocked. When a patient experiences pain over a longer period of time, this function will, however, cease, despite the periphery sensitization still being active and in spite of the wound being, potentially, healed. This essentilly drives the feeling of being in pain after the trauma has healed. Furthermore, we see a sensitization process in the brain leading to secory and motor impairments. When Thalamus is sensitized, it alters that function amongst others and the system designed to relieve pain, diminishes.