Neuropathic pain is distinct from other types of pain. If a person breaks a bone, pain signals are carried via nerves from the site of the trauma to the brain. With neuropathic pain, however, pain signals originate in the nerves themselves.
How Neuropathic Pain Develops
In many cases, the nerves become damaged or dysfunctional after responding to an injury or trauma, causing hypersensitivity to pain. The nerves then send faulty signals of pain even when the injury has healed. The initial injury can occur in either the peripheral or central nervous system.
Neuropathic pain, or neuropathy, is a chronic condition, meaning it does not go away. Instead, the pain becomes the disease process. The terms sensory peripheral neuropathy and peripheral neuritis are sometimes used to describe neuropathy affecting the peripheral nerves.
An estimated 7 to 10% of people have neuropathic pain. This article examines neuropathy and chronic back pain, and how the two conditions are related.
When Back Pain Causes Neuropathy
Neuropathy can result from any type of pain that compresses or impinges on a nerve. A herniated disc, for example, could press against a nearby nerve, causing pain. Neuropathic pain originating from the back or spine may include:
- Chronic pain radiating down the leg (lumbar radiculopathy, or sciatica)
- Chronic pain radiating down the arm (cervical radiculopathy)
- Pain following back surgery that starts gradually and persists, commonly called failed back surgery syndrome
Diabetes and regional pain syndrome (RPS), are common causes of neuropathy. Additional causes of include injury, disease, infection, exposure to toxins, and substance abuse. It is not always possible to pinpoint the cause.
Why Early Treatment is Crucial
Early treatment is important, since more aggressive treatment may be needed if symptoms are not addressed soon.
Over time, exposure to significant pain can cause changes to the central nervous system that make the body become more sensitive to even slight touch—a phenomenon known as central sensitization.
As with other types of chronic pain, delays in treatment may also make other health problems more likely. Depression, anxiety, difficulty sleeping, and an inability to work and take part in other activities are some health issues associated with untreated neuropathy.
Understanding Neuropathy Symptoms
Neuropathic pain symptoms are often unpredictable, and vary significantly from person to person. Pain may be triggered by a specific stimulus, or occur on its own. In the case of a sudden impact, the area surrounding the site of the trauma may be affected in addition to the immediate area.
Some people have constant pain, while others may experience pain that occurs on and off.
Neuropathy May Limit Daily Functioning
Neuropathic pain often makes movement painful, leading an individual to limit mobility. Being sedentary can cause muscles to weaken, further restricting physical functioning. Many people with neuropathy are unable to work.
Back pain or other pain caused by neuropathy is typically described in the following terms:
- Severe, sharp, electric shock-like, shooting, lightning-like, or stabbing
- Deep, burning, or cold
- Persistent numbness, tingling, or weakness
- Pain that travels along the nerve path into the arms, hands, legs, or feet
Skin in the painful area may be discolored, appearing more pink or red than usual. In some cases, the skin may have a blue or mottled appearance. Changes in color are usually related to changes in blood flow. Some individuals also experience swelling.
Many people with neuropathic pain also experience sleep difficulties and depression, both of which can increase the perception of pain. A multifaceted pain management approach may be beneficial to address all aspects of the person’s health.
Unusual Sensations in Neuropathy
People with neuropathic pain may experience sensations in unusual ways, such as:
- Hypersensitivity to light touch that would be barely noticeable to others, is known as allodynia. The feeling of clothing against the skin, for instance, could trigger a reaction.
- Hyperalgesia is an extreme sensitivity to something slightly painful to others.
- An unusually low sensation to hot or cold is called hypoesthesia.
- An electric-shock or pins-and-needles feeling when there is no contact, a known as paresthesia.
Sensory tests may be conducted to see how the individual responds to different types of physical contact.
Treatment for Neuropathic Pain
Electromyography and nerve conduction studies, blood tests, and diagnostic tests such as magnetic resonance imaging (MRI) may be used to determine the cause—or rule out a potential cause. Test results can be helpful in finding the most effective therapy.
Some cases are more straightforward than others. If a nerve is compressed by a herniated disc, for instance, decompression surgery can relieve the pain by removing the pressure on the nerve.
If no underlying cause of the pain is found, treatment typically emphasizes pain relief. There is no single medication that eliminates the symptoms of neuropathy, but a combination of medications and treatments may be helpful Care from an interdisciplinary pain management team may be advised for individuals with neuropathic pain.
Anatomy Of Nerve Pain
The human nervous system has a tremendous capacity to constantly relay vital messages throughout the body. If this complex system is damaged, nerve signals can go awry, causing intense pain.
The spinal cord is the main transportation hub of the body’s central nervous system, carrying signals from the brain to nerves throughout the body. Nerves coming from and leading to all parts of the body enter and exit the spinal cord along its entire length.
The Spinal Cord and Peripheral Nerves
Thirty-one pairs of spinal nerves exit the spinal cord through openings between the vertebrae. The point at which a nerve exits the spinal cord is called a nerve root. The nerve root then branches out into many smaller peripheral nerves that control different parts of the body.
Damage to any part of the central nervous system or peripheral nerves can cause neuropathic pain.
A nerve that exits the lower back has peripheral branches that extend all the way down to the toes. Peripheral nerves comprise the peripheral nervous system. The peripheral nerves include both motor nerves and sensory nerves:
- Sensory nerves are nerves that receive sensory stimuli, telling us how something feels—whether it is hot, cold, or painful. These nerves are made up of nerve fibers, called sensory fibers (mechanoreceptor fibers sense body movement and pressure against the body, and nociceptor fibers sense tissue injury).
- Motor nerves lead to the muscles and stimulate movement. They are made up of nerve fibers called motor fibers.
Neuropathy may damage either the inner or outer part of the nerve cell. The axon is the inner information pathway of the nerve cell. Myelin—the fatty outer sheath—protects the nerve cell and assists in conveying information throughout the nervous system.
Symptoms of peripheral neuropathy generally appear first in the body’s longest nerves, initially affecting the feet, then the hands. Over time, the symptoms typically move up the arms and legs.
How Nerves Cause Pain
Spinal structures and nerves are in close proximity, creating the potential for irritation and pressure on the nerves. Many structures in the spine can cause back pain, such as when:
- Large nerve roots that go to the legs and arms are irritated
- Smaller nerves that innervate the spine are irritated
One common example of nerve pain occurs when a person has a lumbar herniated disc. The discs between the vertebrae can herniate and press against a nearby spinal nerve root. Leakage of the gel-like material inside the disc may also aggravate a nerve.
After the nerves are damaged and neuropathy develops, abnormal signals from the peripheral nervous system and the central nervous system prevent the pain from easing.
Types of Back Pain
Strategies to address back pain vary widely, depending on the type of pain as well as other factors.
Learning about the major types of back pain can be helpful for people with back pain who are considering their treatment options. The medical community typically places back pain in one of the following categories:
When Pain Is Clear-Cut: Nociceptive Pain
The type of pain most people know best is called nociceptive pain. Our body has sensors, called nociceptors, which spot potentially harmful stimuli. These receptors alert us to an injury to a muscle, soft tissue (ligaments, tendons), bones, joints, or skin (or other organs). Pain signals are then relayed to the brain and the central nervous system, resulting in a feeling of pain. Nociceptive pain is also called somatic pain.
Nociceptive pain is often described as a deep aching, throbbing, gnawing, or soreness. Common examples of nociceptive pain related to back pain include pain after trauma, such as back pain after a car accident or a fall; pain after back surgery; and arthritis pain. Nociceptive pain is usually localized and eases as the injury heals.
When Nerves Malfunction: Neuropathy
Pain caused by damage or injury to the nerve tissue is called neuropathy, or neuropathic pain. Nerve damage can result from an infection or injury elsewhere in the body. It is not known why some injuries lead to neuropathy, while others do not. Once the damage is done, the nerves continue to send pain signals long after the original injury has healed.
Sciatica is a symptom of back-related neuropathic pain. It occurs when something presses against a nerve root in the lower back, triggering pain and numbness along the sciatic nerve, stretching from the buttocks to the feet. Other examples include pain that travels from the spine down the arm, and pain that persists after back surgery.
It is thought that some cases of prolonged nociceptive pain may progress to neuropathy.
Acute vs. Chronic Pain
Within the categories of nociceptive and neuropathic pain, pain can be further broken down into acute and chronic pain, which differ greatly in form and function:
- With acute pain, the severity of pain is tied to the level of tissue damage. The body has a protective reflex to avoid this kind of pain: the reflex to pull back quickly after touching a sharp object. Acute pain is a sign of injured or diseased tissue; when the underlying problem is cured, the pain goes away. Acute pain is a form of nociceptive pain.
- Chronic pain does not serve a protective or other helpful biological function. Instead, the nerves continue to send pain messages after the earlier tissue damage has healed. Neuropathy is a type of chronic pain.
Causes of Neuropathic Pain
Neuropathic pain differs from other types of pains and in order to start talking about neuropathic pain, it’s important to remember what pain actually is. So, nociceptive pain or pain that we sense usually is nerves transmitting an impulse and letting us know that there is a damage or injury to part of our body. Neuropathic pain is an actual pathology of the nerve itself. Nerve consists of its body, which is the axon, which is the part that usually gets injured and when that axon is injured what happens is abnormal transmission of impulses. It’s important to remember that it’s not nerves communicating an injury elsewhere, but the process in the nerves themselves.
Neuropathic pain itself presents differently from other types of pain. So, neuropathic pain is likely to be severe. It is usually sharp. It is electric shock-like sensation that people usually describe. It is lightning or lancinating type of pain that most people talk about when they describe neuropathic type of pain. Accompanying that, it can be a deep burning or, at the same time, it can also present as coldness in the limbs or distribution of that nerve. It also comes, at times, with persistent numbness, tingling, or weakness of the muscles that nerve supplies.
Neuropathic pain usually travels along the path of the nerve itself. Because the nerves have different function – some nerves are motor nerves, some nerves are sensory nerves – if the sensory part of the nerve is affected, it can alter sensation. Now, it can actually decrease sensation – in other words, create numbness – or it can heighten sensation where normal stimuli are now painful or altered – so something that would usually be a normal muscle sensation, such as light touch, can become a painful sensation.
There are many causes for neuropathy or neuropathic pain affecting the nerves. Some of those are compression of the nerve. Now, compression of the nerve can occur anywhere along the path of the nerve. It can be as it exits the spine and travels onward, as in radiculopathy – or in other words, pain arising from compression of the spinal nerve before it exits the spinal column – or it can be peripheral nerve compression. And many of us know what it feels like when we cross our legs and the leg goes numb – that is compression of the peripheral nerve and usually that recovers by itself, but if that compression remains for a longer period of time, then that can become not necessarily permanent, but the recovery from that can take months and sometimes even a whole year.
Other sources of the neuropathy can be systemic processes, such as diabetes. Diabetes is a microvascular process decreasing the supply of nutrients to tissues as well as nerves and that tends to be what’s called a “length-dependant process,” in other words, nerves that are longer tend to be affected first and that’s why people with diabetic neuropathy tend to feel their feet being affected first because the nerves are that much longer, so those nerves tend to be affected first, then the hands follow that because they are the next longest nerves in the body.
That being said, any process that can damage tissue can also damage nerve tissue. So, what I mean is treatments like chemotherapy – there are different chemotherapy agents that can alter different processes that the nerves depend on and some are actually neurotoxic – in other words, they are damaging the nerves directly. Now, chemotherapy affecting the nerves can appear at the time of the treatment, but it can also be a delayed presentation of that neuropathy. Also, radiation; a process that radiation causes, in the long run, can come up as post-radiation fibrosis. In other words, tissues fibrose and contract and can affect the nerves and that can cause neuropathy as well.