Diffuse noxious inhibitory controls (DNIC) or conditioned pain modulation (CPM) refers to an endogenous pain modulatory pathway which has often been described as "pain inhibits pain". It occurs when response from a painful stimulus is inhibited by another, often spatially distant, noxious stimulus.
Mechanism
Noxious stimuli activate the endings of
nociceptive
In physiology, nociception , also nocioception; ) is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular ...
C and A delta nerve fibers, which carry the signal to
neurons
A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
. DNIC refers to the mechanism by which dorsal horn
wide dynamic range neuron The wide dynamic range (WDR) neuron was first discovered by Mendell in 1966. Early studies of this neuron established what is known as the Gate control theory, gate control theory of pain. The basic concept is that non-painful stimuli block the path ...
s responsive to stimulation from one location of the body may be inhibited by noxious stimuli (such as heat, high pressure or electric stimulation) applied to another, remote location in the body. The inhibition is thought to originate in the brain, and is thought to affect both wide dynamic range and nociception-specific neurons in the dorsal horn.
Studies investigating gender differences in DNIC have shown mixed results with the effect dependent upon experimental methodology and measurement method.
pain tolerance
Pain tolerance is the maximum level of pain that a person is able to tolerate. Pain tolerance is distinct from pain threshold (the point at which pain begins to be felt).algometer'' with a rubber top is used to apply pressure to a person's finger or toe. The pressure at which the first sensation of pain is felt is recorded as PPT. The pressure is increased further and noted when the person says the pain is intolerable. This higher value is recorded as PTol. A second noxious stimulus (such as ice water) is then applied to a different part of the body and PPT/PTol measured. DNIC response is defined as an increase in the value of PPT during the second noxious stimulation.
Clinical use
The DNIC model is used frequently to quantify the central pain sensitization in chronic pain patients. DNIC inefficiency (or lower DNIC) has been implicated as a risk factor for development of chronic pain and pain syndromes. Chronic pain disorders such as temporomandibular disorder and fibromyalgia have been associated with DNIC inefficiency. On the other hand, greater DNIC response is related to less pain, better physical functioning, and better self-rated health.
Diabetic neuropathy
Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...
patients with low DNIC are more likely to benefit from treatment with
duloxetine
Duloxetine, sold under the brand name Cymbalta among others, is a medication used to treat major depressive disorder, generalized anxiety disorder, obsessive–compulsive disorder, fibromyalgia, neuropathic pain, central sensitization, and ...
and tapentadol, which are considered to restore altered descending modulation.
DNIC forms the basis for the use of
counterirritant
A counterirritant is a substance which creates irritation or mild inflammation in one location with the goal of lessening discomfort and/or inflammation in another location. This strategy falls into the more general category of counterstimulatio ...
to reduce pain.
See also
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Counterirritant
A counterirritant is a substance which creates irritation or mild inflammation in one location with the goal of lessening discomfort and/or inflammation in another location. This strategy falls into the more general category of counterstimulatio ...
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Counterstimulation
Counterstimulation is a treatment for pain based on distraction.
A basic example is the practice of rubbing a fresh bruise, so that attention is paid to the sense of touch and pressure, rather than to the pain of the injury. Liniment and "medicat ...
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Pain
Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...