The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.”

Neuropathic pain is the result of an injury or malfunction in the peripheral or central nervous system. The pain is often triggered by an injury, but this injury may or may not involve actual damage to the nervous system.

CLASSIFICATION OF PAIN

If we start with the concept of pain as a disease, then treatment begins with a pain diagnosis. Pain has been categorised in a variety of different ways, a particularly useful division is based on the kind of damage it causes:

According to The American Journal of Managed Care (AJMC) “Nociceptive pain results from activity in neural pathways secondary to actual tissue damage or potentially tissue-damaging stimuli. Neuropathic pain is chronic pain that is initiated by nervous system lesions or dysfunction and can be maintained by a number of different mechanisms.”

NOCICEPTIVE PAIN

Nociceptive pain is the most common type of pain and is caused by the detection of noxious or potentially harmful stimuli by the nociceptors around the body. It represents the normal response to noxious insult or injury of tissues such as skin, muscles, visceral organs, joints, tendons, or bones.

Dr Steven Richeimer (The Richeimer Pain Institute and Chief, Division of Pain Medicine, Keck School of Medicine, University of Southern California) gives the following examples of nociceptive pain: “sprains, bone fractures, burns, bumps, bruises, inflammation (from an infection or arthritic disorder), obstructions, and myofascial pain (which may indicate abnormal muscle stresses).

Nociceptors are the nerves which sense and respond to parts of the body which suffer from damage”, explains Richeimer. “They signal tissue irritation, impending injury, or actual injury. When activated, they transmit pain signals (via the peripheral nerves as well as the spinal cord) to the brain. The pain is typically well localised, constant, and often with an aching or throbbing quality. Visceral pain is the subtype of nociceptive pain that involves the internal organs. It tends to be episodic and poorly localised.

“Nociceptive pain is usually time limited, meaning when the tissue damage heals, the pain typically resolves. (Arthritis is a notable exception in that it is not time limited.) Another characteristic of nociceptive pain is that it tends to respond well to treatment with opioids.”

NEUROPATHIC PAIN

“Neuropathic pain is the result of an injury or malfunction in the peripheral or central nervous system. The pain is often triggered by an injury, but this injury may or may not involve actual damage to the nervous system,” says Richeimer. Nerves can be infiltrated or compressed by tumours, strangulated by scar tissue, or inflamed by infection. The pain frequently has burning, lancinating, or electric shock qualities. Persistent allodynia, pain resulting from a nonpainful stimulus such as a light touch, is also a common characteristic of neuropathic pain. The pain may persist for months or years beyond the apparent healing of any damaged tissues. In this setting, pain signals no longer represent an alarm about ongoing or impending injury, instead the alarm system itself is malfunctioning.

“Examples [of neuropathic pain] include post herpetic (or post-shingles) neuralgia, reflex sympathetic dystrophy/causalgia (nerve trauma), components of cancer pain, phantom limb pain, entrapment neuropathy (e.g., carpal tunnel syndrome), and peripheral neuropathy (widespread nerve damage). Among the many causes of peripheral neuropathy, diabetes is the most common, but the condition can also be caused by chronic alcohol use, exposure to other toxins (including many chemotherapies), vitamin deficiencies, and a large variety of other medical conditions–it is not unusual for the cause of the condition to go undiagnosed.

“Neuropathic pain is frequently chronic, and tends to have a less robust response to treatment with opioids, but may respond well to other drugs such as anti-seizure and antidepressant medications. Usually, neuropathic problems are not fully reversible, but partial improvement is often possible with proper treatment,” Richeimer concludes.

Much neuropathic pain is chronic. Examples of pain caused by damaged nerves include:

  • Central pain syndrome
  • Complex regional pain syndrome
  • Diabetic peripheral neuropathic pain
  • Shingles and postherpetic neuralgia
  • Trigeminal neuralgia

PAIN INTENSITY

The University of Wisconsin School of Medicine and Public Health (UWSMPH) says pain intensity can be broadly categorised as mild, moderate, and severe. “It is common to use a numeric scale to rate pain intensity where 0 = no pain and 10 is the worst pain imaginable.”

  • Mild: <4/10
  • Moderate: 5/10 to 6/10
  • Severe: >7/10

PAIN DURATION

UWSMPH also emphasises the classification of pain based on duration:

  • Acute pain: pain of less than 3 to 6 months duration
  • Chronic pain: pain lasting for more than 3-6 months, or persisting beyond the course of an acute disease, or after tissue healing is complete.
  • Acute-on-chronic pain: acute pain flare superimposed on underlying chronic pain.

Scotland’s Pain Concern describes acute pain as the pain you get after you bang your knee, have an operation or a heart attack. “It lasts for a limited period of time and usually responds well to medication.

“Chronic pain is pain which persists or recurs for more than three months. It is now recognised as a condition in its own right.”

“Many acute pains are like an alarm telling us something is wrong,” explains the British Pain Society. “Most minor ones are easy to treat; others may be a sign of something more serious. For example the pain of a broken leg will make us rest the leg until it heals. Here the pain is helping.”

Chronic pain on the other hand serves no useful purpose. “The messages from the warning system linked to long-term conditions like arthritis or back pain are not needed – just annoying. Over time, it may affect what we can do, our ability to work, our sleep patterns. It can have a strong negative effect on our family and friends too.”

GENES AND PAIN

Genes also have a role to play in the story of pain, says Professor Ana Valdes (Associate Professor, Faculty of Medicine and Health Sciences at the University of Nottingham). Her research is helping to explain why some people develop conditions such as fibromyalgia, migraine or rheumatoid arthritis and others do not based on differences in our makeup at the molecular level. Even our psychological responses to pain are affected by differences in the nervous system. Valdes believes these more sophisticated approaches to pain offer hope of effective treatment in the future.

TECHNIQUES THAT HELP WITH PAIN MANAGEMENT

  • deep breathing
  • relaxation
  • positive imagery
  • thought distraction
  • heat or cold compresses (or a combination of the two)
  • reducing stress in your life
  • remaining positive
  • exercise