Accurate Education – Pain Definitions

Pain – Definitions and Terms

Pain is defined as:

“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”



Understanding Pain:

Neurobiology of Pain

Neuropathic (Nerve) Pain


Neurobiology of Opioids

Opioid Tolerance

Central Sensitization


See below for more definitions and terms


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“The whole purpose of education is to turn mirrors into windows.”

 – Sydney Harris


Definitions and Terms Related to Pain:



A painful response to a normally innocuous, or non-painful stimulus

Allodynia is a term that describes the experience of pain from a stimulus which does not normally provoke pain. Like hyperalgesia, allodynia can be a consequence of central sensitization. It is also commonly accompanies fibromyalgia, diabetic neuropathy and chronic headaches. An example is a patient with diabetic neuropathy whose feet are sensitive to putting on socks.

For more information: Assessment and Management of Central Sensitization



Apoptosis is a form of programmed cell death that physiologically plays a role in embryogenesis, cell differentiation, proliferation/homeostasis, and as a defensive mechanism to remove infected, mutated, or damaged cells. Under normal conditions, a balance between apoptosis and cell survival is important in the development of multicellular organisms and in the regulation and maintenance of cell populations in tissues. In fact, dysfunction of the apoptotic program is implicated in a variety of pathological conditions. Thus, impaired apoptosis can result in cancer, auto-immune disorders such as Lupus or Rheumatoid Arthritis and the spread of viral infections. Excessive apoptosis can lead to neurodegenerative disorders such as Alzheimers and Parkinson’s Disease and cardiovascular disease.


Central pain:

A subset of neuropathic pain caused by a lesion or disease of the central somatosensory nervous system

Central pain is pain arising from a lesion in the central nervous system – such as thalamic pain following stroke – or deafferentation pain (stemming from loss or interruption of sensory nerve fiber transmissions.


Central Pain Syndrome

Central pain syndrome is de!ned by the National Institute of Neurological Disorders and Stroke (NINDS) as “a neurological condition caused by damage to or dysfunction of the central nervous system.” Central Pain Syndrome can occur as a result of stroke, multiple sclerosis, neoplasm, epilepsy, CNS trauma, or Parkinson’s disease. Patients with central pain syndrome may experience localized pain, burning, and/or numbness in speci!c parts of the body, or throughout the body.


Central sensitization:

Increased responsiveness of nociceptive neurons in the central nervous system to normal or subthreshold sensory input.


Central Sensitization is a process of hyper-responsiveness to sensory stimuli which is a result of chronic pain-induced changes in the spinal cord and brain. It can be an important contributing process to the chronic pain experience.

For more information: Assessment and Management of Central Sensitization


Chronic Pain

Chronic pain is inconsistently defined but is generally considered to be pain that persists beyond the normal course of healing, with a time frame usually defined as 3 months or longer.


Chronic Pain Syndrome

Chronic Pain Syndrome is chronic pain associated with signi!cant psychosocial dysfunction. The psychosocial problems may include depression, drug dependence, anxiety, and other manifestations including pain complaints that are out of proportion to the physical findings. Chronic pain syndrome is not synonymous with chronic pain.



Cytokines are small intracellular regulatory proteins that are released by immune cells in the event of damage or injury. Cytokines can be pro-inflammatory or anti-inflammatory and they play an important role in the development and maintenance of chronic pain. Cytokines sensitize peripheral nociceptors (nerve endings – see below) and trigger pain signals to the spinal cord, but they may also cross the blood brain barrier and participate in central sensitisation processes in the spinal cord and brain. Examples of cytokines relevant to pain include Tumour Necrosis Factor (TNF), Interleukin 1 (IL-1), and Interleukin 6 (IL-6) and others. IL-6 appears to be the best biomarker for the presence of chronic systemic inflammation and nerve pain and your physician may use blood tests to monitor IL-6 levels.


Deafferentation pain:

Pathological pain condition associated with a partial or complete loss of sensory input from a part of the body after lesions in somatosensory pathways, often as a result of reorganization in the central nervous system. Common examples include phantom limb pain and brachial plexopathy.


Descending modulation:

The process by which pathways that descend from the brain to the spinal cord modify incoming somatosensory information so that the perception of and reactions to somatosensory stimuli are altered, resulting in increased or decreased pain.



electric shock phenomenon


Ectopic discharge:

Trains of ongoing electrical nerve impulses that occur spontaneously without stimulation or originate at sites other than the normal location (or both). This phenomenon typically occurs after nerve injury.


Ephaptic transmission:

The phenomenon by which two independent nerves communicate with each other through an artificial synapse, which often develops after injury to the insulating myelin sheath that normally prevents crosstalk between parallel nerves.


Glial Cells

Glial cells, sometimes called neuroglia or glia, are non-neuronal cells (not nerve cells) found in the central and peripheral nervous system.  The role of glia include synapse formation, synapse maturation, and plasticity and the rapid conduction of action potentials, as well as immunological functions in the nervous system. Glial cells are generally distinguished in subclasses based on their diverse morphology and function. These include microglia, the immunocompetent and specialized brain macrophages; astrocytes, which represent the major glial component in the CNS and constitute up to 20–50% of the brain volume; NG2-glia, a peculiar type of glial cells that receive direct synaptic input from neurons; Schwann cells and oligodendrocytes form layers of myelin around neuronal axons in the peripheral and central nervous system, respectively.


Glial cells function to maintain balance in nerve activity, they form myelin (the coating of some nerve cells), and provide support and protection for neurons (nerve cells). Glial cells are derived from the immune system, the most common of which are microglia cells and astrocytes. Glia cells provide a supportive matrix for nerve cells, supplying nutrients and oxygen and aid in the repair of damaged cells. However, when activated, glial cells also are important in the evolution and maintenance of chronic nerve pain. They may play a role in opioid function including opioid-induced hyperalgesia and opioid tolerance. It is believed that pathologic glial cell activation plays a significant role in the evolution of fibromyalgia pain, central sensitization and other chronic pain syndromes. Early studies suggest that medications or supplements that inhibit glial activation may reduce the development of chronic nerve pain or reduce the severity of existing nerve pain.

For more information: Neurobiology of Pain



Hyperalgesia is an exaggerated, increased painful response to a stimulus which is normally painful. Hyperalgesia can be a consequence of central sensitization and is also thought to occur with chronic exposure to opioids, although the clincal significance of this is uncertain.

For more information: Assessment and Management of Opioid Induced Hyperalgesia



increased sensitivity to mild painful stimuli.



pain produced by subthreshold stimuli


Inflammatory Pain (“Arthritis”)

The pain associated with arthritis is sometimes referred to as inflammatory pain due to the underlying component of inflammation contributing to the pain and disease process. While not strictly a separate type of pain, arthritis pain is often treated differently due to the focus on reducing inflammation thereby reducing the associated pain. Recent research however show us that the pain and disease process of arthtitis also involves the underlying bone of the affected joint and there is a neuropathic component to the pain of arthritis. The use of neuropathic pain agents has been shown to be helpful in arthritis pain. Treating arthritis with NSAIDs offers both analgesic and inflammatory benefits although the dosage and duration of treatment may vary between the two (see: NSAIDs).

For more information:  Arthritis and CAM Treatment of Arthritis


Medication Abuse and Misuse

These two terms are widely used, yet their definitions are as varied as there are individuals using them. The unfortunate consequence of this is a grave lack of understanding regarding their incidence, risks and consequences. For the purposes of this web site, the following definitions apply:


Medication Abuse:

“Medication Abuse” is defined as the use of a drug for purposes other than as indicated or prescribed. “Purposes other than as indicated or prescribed” include using a medication such as a pain medication for sleep, anxiety, to improve mood or to get high.


Medication Misuse:

“Medication Misuse” is defined as the use of a drug for purposes as indicated or prescribed, but at doses other than as indicated or prescribed. Medication misuse includes taking a prescription medication as previously or routinely prescribed, but without a current prescription. It also includes taking a currently prescribed medication at doses higher than as prescribed.



Metabolism refers to the life-sustaining chemical transformations within the cells of living organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of wastes. These chemical transformations are mediated by enzymes and allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells.


Metabolism is usually divided into two categories: catabolism, the breaking down of organic matter and anabolism, the building up of components of cells such as proteins and nucleic acids. Usually, breaking down components releases energy and building up components consumes energy.



Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, catalytic activity of their own (usually as a cofactor to an enzyme), defense, and interactions with other organisms.



Metabolomics is the scientific study of chemical processes involving metabolites. Specifically, metabolomics is the “systematic study of the unique chemical fingerprints that specific cellular processes leave behind”, the study of their small-molecule metabolite profiles.


Neuropathic pain (“Nerve Pain”):

Pain caused by a lesion or disease of the somatosensory nervous system.

Nerve pain is usually perceived as burning, electric, shock-like, tingling or sharp and may start at one location and shoot, or “radiate” to another location (like sciatica). Neuropathic pain can be “peripheral,”  (outside the central nervous system),”  like carpal tunnel pain or “central,” originating in the spinal cord or brain.  Neuropathic pain is often a disease process, not simply the symptom of one.

For more information:  Assessment and Management of Neuropathic Pain



Changes in neural pathways and synapses that result from bodily injury or changes in behavior, the environment, or neural processes. This is consistent with the concept that the brain is a dynamic organ that constantly changes in response to internal and outside events throughout life.



The neural responses of encoding and processing noxious stimuli


Nociceptive pain:

Pain that arises from the activation of peripheral nerve endings (nociceptors) that respond to noxious stimulation. Nociceptive pain arises from actual or potential damage to non-neural tissue and can be categorized as visceral or somatic.


Nociceptive pain is caused by activation of neural pathways in response to damaging or potentially damaging stimuli to body tissue such as occurs with chemical or mechanical trauma or burns.  It is usually described as a sharp, aching, or throbbing pain. Nociceptive pain is further divided into “visceral” pain, originating from the organs inside the body,  and “somatic” pain, originating from muscles, bone and skin. Visceral pain is often vague, difficult to describe and hard to localize. Nocicptive pain is usually a symptom of a disease process.



Nootropics or “smart drugs” are substances that serve to enhance cognition or improve brain performance.


Noxious stimulus:

A stimulus that damages or threatens to damage normal tissues


NSAIDs (Non-Steroid Anti-Inflammatory Drugs):

The NSAIDs are analgesics for mild to moderate pain and are usually the first type of analgesic taken for pain along with acetoaminophen (not an NSAID). NSAIDs work by inhibiting two enzymes that are responsible for inflammation and pain, cyclooxygenase-1 and cyclooxygenase-2 (Cox-1 and Cox-2). NSAIDs that inhibit both Cox-1 and Cox-2 are considered non-selective NSAIDs (ns-NSAIDs) whereas NSAIDs that inhibit only Cox-2 are referred to as selective Cox-2 inhibitors.


NSAIDs that are available over the counter (OTC) without prescription include ibuprofen (Advil, Motrin) and naproxen (Naprosyn, Anaprox, Aleve) and aspirin. Prescription versions of the OTC NSAIDs are available and usually covered by insurance. Other common prescription NSAIDs include diclofenac (Voltaren), Mobic (meloxicam) and others.


Topical NSAIDs:

Topical NSAIDs in many cases are equally effective for pain control and are the recommended first choice to begin treatment with an NSAID. There are many effective OTC topical creams with NSAIDs. Prescription NSAIDs include diclofenac (Voltaren Gel, Pennsaid and Flector Patches). Compounded topical medications used for pain usually consist of a combination of different medications with analgesic properties, in addition to diclofenac



Pain is defined as:

“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”


Paresthesias:  numbness or tingling


Peripheral sensitization:

A lowering of the stimulus (pain) threshold for nociceptor activation and an increased frequency of nerve impulse firing in response to stimulation (hyperexcitability). Peripheral sensitization is often found at the site of tissue damage or inflammation



Pain perceived to arise from a body part that has been amputated



Pharmacodynamics considers processes such as receptor binding type and location, alterations in signal transduction, and cross-tolerance – including how medications work.



Pharmacokinetics considers how the production of metabolites, alterations in metabolic enzyme activity, and modulation of drug transporter expression or function are addressed – including how quickly medications are eliminated.



“Referred” Pain

Referred pain often makes establishing a diagnosis challenging. When the pain originates in one location but is perceived in, or travels to, another location the process is termed “referred” pain. Many people with chronic low back pain also experience “sciatica,” pain that originates in the low back and travels down one or both legs – a common example of referred pain.


The source of referred pain is often difficult to identify accurately. “Sciatica,” so named after the sciatic nerve implying that pain traveling from the low back into the lower extremities is generated by compression or other pathology of the sciatic nerve. Unfortunatly, it not so simple. Many tissues have the capacity to refer pain to a different location. Best known of the referred pains are the dermatomal patterns of pain generated from a specific nerve root in the lower back that give rise to specific patterns of pain from the low back to the great toe for example. This is a “true” sciatica, referred pain from the sciatic nerve. 


However other tissues in the back including the facet joints in the spine, muscles and fascia (the tissue surrounding muscles) can also refer pain to the lower extremities. Referred nerve pain is likely to be perceived as typical neuropathic pain: burning, electric, tingling and usually well localized. Referred pain from the facet joints is more likely to be sharp or dull and aching and likely to be more vaguely localized, usually not below the knees. This case in point underscores the need to evaluate any pain carefully, especially referred pain, to establish an accurate diagnosis. If the diagnosis is wrong, the treatment is unlikely to be effective as many patients victimized by unsuccessful lumbar surgery for “sciatic” pain  will testify to.


Sympathetically maintained pain:

Pain that is enhanced or maintained by a functional abnormality of the sympathetic nervous system, such as functional sympathetic afferent coupling or increased expression of adrenergic receptors at the peripheral terminals of nociceptive afferent fibers.


Visceral Pain:

The pain associated with internal organs and tissues is referred to as “visceral” pain. It tends to be somewhat vague when attempting to localize where it arises and it is often perceived as dull, aching or cramping although it may be burning or sharp and stabbing. Visceral pain is often perceived in a different location than where the problem originates (see “referred pain,” below). For example, the pain associated with a heart attack is often perceived down the left (or right) arm. Visceral pain does not generally respond well to neuropathic pain agents though it may respond well to NSAIDs, especially menstrual pain.



Progressive increase in the frequency and magnitude of firing of dorsal horn neurons produced by repetitive activation of C fibers above a critical threshold, leading to a perceived increase in pain intensity

Emphasis on Education


Accurate Clinic promotes patient education as the foundation of it’s medical care. In Dr. Ehlenberger’s integrative approach to patient care, including conventional and complementary and alternative medical (CAM) treatments, he may encourage or provide advice about the use of supplements. However, the specifics of choice of supplement, dosing and duration of treatment should be individualized through discussion with Dr. Ehlenberger. The following information and reference articles are presented to provide the reader with some of the latest research to facilitate evidence-based, informed decisions regarding the use of conventional as well as CAM treatments.


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