Central sensitization

Central sensitization is a nervous system condition that typically results in chronic pain. In the event of central sensitization, the nervous system undergoes a process known as wind-up. During wind-up, the body becomes regulated in a persistent state of elevated reactivity. This state of heightened reactivity lowers one’s natural threshold for pain and causes the body to maintain the sensation of pain for extended periods, even after the initial injury. While the exact cause of central sensitization remains unknown, it is believed to be triggered by events such as illness, infection, physical injury, or emotional distress. There may also be genetic factors involved. In any case, central sensitization results in both heightened sensitivity to pain and the sense of touch. It may cause sensitivity to light, smell, and sound as well. Treating central sensitization can be as challenging as identifying its cause. In most cases, treatment involves both medication and lifestyle changes.

Background

Central sensitization is a condition of the human nervous system. The nervous system is a complex network of neurons and other cells that allows a person to feel, think, and breathe. It includes two main components: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord. The PNS includes all of the nerves and nerve cells that run throughout the body and send messages to and from the CNS. The basic working unit of both the CNS and PNS is the neuron. Neurons are special cells that transmit information to other cells or muscles. In the CNS, neurons are encased in bone. In the PNS, neurons are found inside or on top of muscles, organs, and skin tissue. Neurons in both parts of the nervous system join together in groups. In the CNS, each of these groupings of neurons is known as a nucleus. In the PNS, a grouping of neuron cell bodies is called a ganglion, and a bundle of neuron tracts is known as a nerve. The main function of the CNS is to process sensory information and send commands to the rest of the body. The PNS is primarily tasked with gathering sensory information, transmitting that information to the CNS, and carrying out the commands it receives from the CNS.

Pain is a response to the stimulation of certain nerve endings. Pain is the result of a complex series of interactions between nerves, the spinal cord, and the brain. There are two main types of pain: acute and chronic. Acute pain is a sudden, often severe form of pain that gradually resolves over time. It is typically associated with injury or illness. Chronic pain is a persistent form of pain that lasts for longer periods of time and is often regarded as a distinct medical condition. While the source of acute pain is usually evident, the cause of chronic pain may be difficult to discern. In any event, pain is essentially the body’s method of alerting a person to danger and signaling that something may be wrong.

Overview

Central sensitization is a condition in which the nervous system experiences wind-up and enters a state of extraordinary sensitivity to certain stimuli. This condition lowers a person’s natural threshold for pain and often leads to long-lasting chronic pain. The two primary characteristics of central sensitization include allodynia and hyperalgesia. Allodynia causes a person to feel pain or discomfort when they come in contact with things that do not usually cause pain. In other words, when the body becomes regulated in a persistent state of high reactivity, a simple touch that would normally be painless will produce a sensation of pain. Hyperalgesia causes a person to perceive a stimulus that typically produces a sensation of pain as even more painful than normal. In short, central sensitization leads to an amplified sensitivity to pain. Clinical guidance described central sensitization–based conditions as arising when persistent sensory signaling leads to structural, functional, and neurochemical changes in the brain and spinal cord.

There is an array of stimuli to which a person can become particularly sensitive when they are dealing with central sensitization. In many cases, a simple light touch can produce considerable pain. Exposure to bright or flashing lights may also produce pain. Loud, grating, or repetitive noise can be triggering in some patients, as can strong odors. Other patients may become sensitive to heat, cold, or both. Certain textures, including scratchy fabric, may also be especially irritating.

While elevated sensitivity to pain is the most common sign of central sensitization, patients may have other symptoms as well, such as headache, nausea, irritation, panic, confusion, or sensory overload. The severity of symptoms may fluctuate over time. In addition, symptoms may be increased when the reactions generated by central sensitization are related to an illness.

There are a number of conditions that are thought to involve central sensitization. The conditions are generally classified under the umbrella term central sensitivity syndromes. Some common central sensitivity syndromes include fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, restless leg syndrome, myofascial pain syndrome, multiple chemical sensitivity, and migraines.

There is no clear consensus on the causes of central sensitization. However, researchers have developed a number of theories on what might cause the condition. Most believe that central sensitization is likely caused by some combination of dysregulation of neurotransmitters, dysfunction of the body’s stress-response system, nervous system inflammation, or some sort of dysfunction with the fight-or-flight response controlled by the autonomic nervous system.

Treatments for central sensitization focus on the management of pain and other symptoms. This approach often involves both medication and lifestyle changes. Medicinal treatment of central sensitization may involve antidepressant or anticonvulsant drugs. Other pharmaceutical treatments such as alpha- or beta-adrenergic-blocking compounds, anti-inflammatories, bisphosphonates, Botox, ketamine, local anesthetics, opioids, calcium-regulating drugs, gamma-aminobutyric acid (GABA) analogs, serotonin and norepinephrine reuptake inhibitors (SNRIs), or vasodilators may also be prescribed. Therapeutic treatments such as physical therapy, mirror box therapy, graded motor imagery, tactile discrimination training, or sensory discrimination training may be beneficial for some patients as well. Neuropsychological approaches to treating central sensitization include cognitive behavioral therapy, Electroencephalography (EEG) biofeedback, relaxation techniques, and hypnosis. Interventional treatments for central sensitization include epidural blockade, intravenous immunoglobulin, intravenous regional sympathetic block, ketamine infusion, selective sympathetic ganglion nerve blocks, and spinal cord stimulators.

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