What's neuropathic pain
Neuropathic pain is defined as pain caused by a lesion or dysfunction in the nervous system. There is no noxious (pain causing) stimulus that is causing the pain. Rather, the pain results from inappropriate signals in the nervous system. Unlike physiologic pain, which serves to warn and protect individuals from possible or actual injury, neuropathic pain serves no useful purpose.
Some examples of peripheral neuropathic pain include:
Postherpetic neuralgia (pain occurring after shingles);
Diabetic neuropathy;
Pain following limb amputation.
Types of Neuropathic Pain
Painful diabetic neuropathy
Having diabetes and high blood sugar levels can damage your nerves, especially those in the legs and feet. This condition – diabetic neuropathy – can cause pain as well as numbness and tingling.
Trigeminal neuralgia
Trigeminal neuralgia is a disorder of the trigeminal nerve – the nerve that supplies sensation to the face and controls some of the muscles involved in chewing. People with trigeminal neuralgia have episodes of severe facial pain that last from a couple of seconds to several minutes.
Post-herpetic neuralgia
About one in every 5 people with shingles (a painful rash is also known as herpes zoster) develops post-herpetic neuralgia – ongoing pain in the area that was affected by the rash. It occurs when the shingles virus damages the underlying nerves, and the resulting pain can last for months or years.
Phantom limb pain
This condition affects people who have had an arm or leg amputated, causing pain or discomfort in the area of the now-missing limb. The exact cause of phantom limb pain is not known, but it is thought to be due to changes in both the nerves of the affected limb and the central nervous system (brain and spinal cord) following amputation.
Mechanisms/pathophysiology
Neuropathic pain results from damage to an afferent pathway that can be the result of a disease, trauma, or dysfunction.
Ectopic nerve activity/Peripheral Sensitization This mechanism is responsible for pain sensed in the absence of external stimuli. Spontaneous nerve activity has been shown in both the injured nerve as well as uninjured neighboring nerves. This spontaneous activity is thought to be related to an increase in voltage-gated sodium channel expression. This increased expression allows for decreased activation thresholds and increased membrane excitability. Additional expressional changes of other channels (i.e. K+) are also likely to occur but are less studied at this point.
Protein regulation is also altered with nerve damage. For example, a protein TRPV1 (transient receptor protein V1) that is activated at noxious stimuli around 40 Celsius is downregulated at injured fibers but upregulated at nearby uninjured fibers. This may decrease the activation temperature (i.e. to 38 Celsius, near body temperature) and result in the sensation of noxious heat/burning stimuli near the site.
Central Sensitization Regular discharge from peripheral nerves causes a release of excitatory neuropeptides and amino acids in the dorsal horn. This leads to phosphorylation of NMDA and AMPA receptors and expression of voltage-gated sodium channels (similar to ectopic nerve activity). This results in neuronal hyperexcitability that can lead to allodynia and hyperalgesia via activation of mechanosensitive A-beta and A-delta afferent fibers connecting with second-order nociceptive neurons.
Inflammatory reaction Inflammation results in activation of microglia in the nerve as well as the dorsal root ganglion. A proinflammatory milieu is created including cytokines, chemokines, substance P, TNF alpha, etc. These factors facilitate neuropathic pain by further enhancing neuron excitability.
What causes neuropathic pain?
Neuropathic pain often seems to have no obvious cause. But some common causes of neuropathic pain include:
Alcoholism
Amputation
Chemotherapy
Diabetes
Facial nerve problems
HIV infection or AIDS
Multiple myelomas
Multiple sclerosis
Nerve or spinal cord compression from herniated discs or from arthritis in the spine
Shingles
Spine surgery
Syphilis
Thyroid problems
What are the Symptoms of Neuropathic Pain Exactly?
Each person’s symptoms of neuropathic pain may be different, but these symptoms are common:
Shooting, burning or stabbing pain
Tingling and numbness, or a “pins and needles” feeling
Spontaneous pain, or pain that occurs without a trigger
Evoked pain, or pain that’s caused by events that are typically not painful, such as rubbing against something, being in cold temperatures, or brushing your hair
A chronic sensation of feeling unpleasant or abnormal
Difficulty sleeping or resting
Emotional problems as a result of chronic pain, loss of sleep, and difficulty expressing how you’re feeling
Complications
Patients with chronic nerve pain may suffer from sleep deprivation or mood disorders, including depression and anxiety.
Because of the underlying neuropathy and lack of sensory feedback, patients are at risk of developing injury or infection or unknowingly causing an escalation of an existing injury.
Treatment and medications that cure neuropathic pain
Treatment of neuropathic pain first entails addressing the underlying problem. For example, if a person has neuropathic pain from diabetes, optimizing blood sugar (glucose) control is an essential next step. Bear in mind, though, enhanced glucose control cannot generally reverse the neuropathy, although it can prevent it from getting worse and ease current symptoms.
As another example, if a medication is causing debilitating nerve pain, removal or a decrease in the dose of the offending drug may be all that is needed.
First-Line Medications
Besides treating the underlying problem, medication is often needed to manage neuropathic pain.
For the vast majority of patients, treatment of neuropathic pain involves taking one of the following:
An antidepressant like Cymbalta (duloxetine) or Elavil (amitriptyline)
An anti-seizure medication like Neurontin (gabapentin) or Lyrica (pregabalin)
Second-Line Medications
Opioids like Vicodin (hydrocodone/paracetamol) and Percocet (oxycodone/acetaminophen) are not as effective for treating neuropathic pain and, thus, are considered second-line treatments. In addition to their questionable benefit, opioids are associated with several side effects.
Meet your doctor (neurologist) if the symptoms persist for unique therapy
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