Types of Pain: Classifications and By Mechanism

Types of Pain: Classifications and By Mechanism

Pain is an uncomfortable and unpleasant sensation stemming from the activation of the nervous system and caused by intense or damaging stimuli. The International Association of the Study of Pain specifically defines it as both an unpleasant sensory and emotional experience “associated with, or resembling that associated with, actual or potential tissue damage.” It is also a common symptom in different medical conditions.

There are different labels used for the classification of pain and defining the mechanisms behind the different types of pain. The most common ones are based on mechanism and these include nociceptive, neuropathic, nociplastic pain

Some pain does not have a physical origin. It is commonly referred to as psychological pain or emotional pain and is technically termed algopsychalia. Researchers describe it as an unpleasant sensation that does not have a definite physical etiology. It is associated with the discrepancy between the ideal and actual perception of self or a product of internal response to psychological, emotional, or behavioral disturbances.

Musculoskeletal Pain: The 3 Major Types of Pain Based on Mechanism

Pain still falls within the realm of physiology. It represents a signal in the nervous system and is indicative of something that is wrong and requires attention. The pain signal comes from an intense stimulus affecting nociceptors and travels through the A-delta and C sensory fibers. Note that these receptors and fibers are part of the sensory neurons of the peripheral nervous system. The signal then travels further from the periphery and to the central nervous system, specifically to the spinal cord and brainstem before it is registered in the brain.

There are three types of pain categorized and differentiated based on their physiological mechanism. They are collectively called musculoskeletal pain and affect bones, muscles, ligaments, tendons, and even nerves. These are nociceptive, neuropathic, and nociplastic pain. Take note of the following:

1. Nociceptive

Nociceptive pain is the most recognizable type of pain. It is caused by an intense stimulus intercepted by nociceptors and leads to the stimulation of sensory nerve fibers. The stimulus can come from different sources or due to different conditions such as external injuries or exposure to extreme temperatures. Feelings associated with nociceptive pain are often described as sharp, aching, and throbbing.

There are three specific classifications of nociceptive pain based on the mode of noxious stimulation. These are thermal pain arising from exposure to heat or cold, mechanical pain which is associated with physical injuries, and chemical pain stemming from the stimuli produced by chemicals released during inflammation.

Furthermore, nociceptive pain is also categorized according to the site of origin. Take note of the following types of nociceptive pain:

• Somatic Pain: Occurs from the intense stimulation of sensory nerves in the tissues of the muscle, bone, or skin. It can be either deep or superficial. Deep somatic pain originates from the skeletal structures, muscles, and tendons while superficial somatic pain originates from the skin, mucous membranes, and other superficial tissues.

• Radicular Pain: A type of nociceptive pain that radiates from the back and hip or into the legs or arms and through the spine. It stems from an inflamed or compressed nerve root. A prime example is an inflamed nerve in the neck that can radiate pain into the arm or hand. Symptoms include tingling, numbness, and muscle weakness.

• Visceral Pain: Occurs when internal organs in the midline of the body such as the stomach, kidneys, and lungs are injured or inflamed. The sensation can be described as vague because it is difficult to localize and is diffuse or distant but is often characterized as deep, dull, throbbing, and pressured or squeezed.

2. Neuropathic

Neuropathic pain is pain due to the damage or disease affecting sensory nerves of the somatosensory system of the greater peripheral and central nervous systems. Some of its common characteristics have been described as burning or coldness in the affected area, “pins and needles” sensations, numbness, and itching.

The exact cause of the damage or disease varies. Specific medical conditions linked to neuropathic pain include multiple sclerosis and spinal cord injury. It is also a symptom of other diseases such as diabetes, metabolic disorders, infections such as herpes zoster infection, cancer affecting the peripheral nerves, exposure to toxins, and nutritional deficiencies.

It is also categorized further according to the site of origin and mechanistic basis or underlying pathophysiology. The two types of neuropathic pain are central neuropathic pain and peripheral neuropathic pain. Take note of the following:

• Central Neuropathic Pain: Results from an injury to the central nervous system specifically caused by vascular origins, infections such as encephalitis and myelitis, trauma to the spinal cord or brain, or neoplastic disorders.

• Peripheral Neuropathic Pain: Result from an injury to the peripheral nervous system or damage to the nerves outside of the spinal cord and the brain. It is characterized by numbness and weakness affecting the extremities such as hands and feet.

There are also different examples of neuropathic pain labeled and categorized based on more specific pathophysiology and in accordance with unique sensations produced. Take note of the following details:

• Hyperalgesia: An abnormally increased sensitivity to pain and hypersensitivity to a painful stimulus that may be caused by damage to nociceptors and other peripheral nerves. This can be experienced in a specific area or diffuse areas of the body.

• Allodynia: This is different from hyperalgesia because the pain comes from a stimulus that does not normally elicit pain but triggers an uncomfortable and unpleasant sensation. It is a clinical feature of different neuropathies and other painful neurological conditions such as migraine and postherpetic neuralgia.

• Dysesthesia: An unpleasant feeling due to an abnormal sense of touch that often presents as pain but may also present a discomforting sensation. It is caused by lesions in the peripheral or central nervous system.

• Phantom: This is pain that feels like it is coming from a part of the body that has been removed due to amputation or an area of the body that was never there in the first place, and from which the brain no longer receives or has never received signals. The sensations originate from a mix-up of signals between the spinal cord and the brain.

3. Nociplastic

The third type of pain based on mechanism is called nociplastic pain. It is also called central sensitization and is considered to be mechanically different from the mechanisms behind nociceptive pain and neuropathic pain. It may also occur in combination with other types of pain or isolation. The location may be generalized or multifocal.

Note that the unpleasant sensation comes from different parts of the body. It is also often widespread and intense. Sufferers may also experience tiredness, as well as difficulties or problems with mood, behavior, sleep, and memory.

The International Association for the Study of Pain formally adopted the concept and term in its taxonomy in 2017. Its exact causes remain not fully understood but some researchers believe that it could stem from the dysfunction of the central nervous system leading to a distorter or sensitized processing of pain signals.

Doctors diagnose this condition based on its clinical features that are differentiated from nociceptive pain and neuropathic pain, lack of response to regular painkillers, and measurement tools such as stimuli tests, measurement of cytokine levels, and magnetic resonance imaging.

Acute vs Chronic: Types of Pain According to Duration and Frequency

There are also two types of pain categorized according to duration or frequency. These are acute pain and chronic pain.

Acute pain occurs suddenly. It is also caused by something specific or from a stimulus that can be readily determined. Specific causes include superficial injuries such as a cut or bruise, broken bone, or pulled muscle. The overall sensation is characterized as sharp with different levels of intensity. It can last as short as less than a minute or as long as 3  months.

Pain is generally seen as transitory and lasts until the stimulus is removed or the underlying mechanism or pathology has been managed.

However, some pain is persistent. This is called chronic pain. It lasts longer than 12 weeks or 3 months despite medication or treatment. It continues even if the injury or medical condition believed to have caused it has healed or gone away. There are also individuals who suffer from this condition even when there is no history of injury or illness.

Researchers have linked chronic pain with conditions such as cancer, arthritis, headache, back pain, and fibromyalgia. It can either have a nociceptive, neuropathic, or even a nociplastic mechanism. Those who suffer from it also suffer from tensed muscles, lack of energy, poor appetite, emotional distress, and behavioral problems.

It is also important to note that the distinction between acute pain and chronic pain has been blurred. Some reference the prescribed 3-month marker while others use shorter or longer markers to differentiate between acute pain and chronic pain.


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