Neuropathic Pain (Nerve Pain)

When the sensory system is impacted by injury or disease, the nerves within that system cannot transmit sensation to the brain. This often leads to numbness or lack of sensation. However, in some cases, individuals experience pain in the affected region. Neuropathic pain does not start abruptly or resolve quickly; it is a chronic condition that leads to persistent pain symptoms. For many patients, the intensity of their symptoms can vary throughout the day. Although neuropathic pain is associated with peripheral nerve problems, injuries to the brain or spinal cord can also cause chronic neuropathic pain.

Neuropathic pain can be contrasted to nociceptive pain, which occurs when someone experiences an acute injury, such as smashing a finger with a hammer. This type of pain is typically short-lived and responsive to common pain medications.

What are the risk factors for neuropathic pain?

Anything that leads to loss of function within the sensory nervous system can cause neuropathic pain. Nerve problems from carpal tunnel syndrome or similar conditions can trigger neuropathic pain. Trauma causing nerve injury can also lead to neuropathic pain. Other conditions that can predispose patients to neuropathic pain include diabetes, vitamin deficiencies, cancer, HIV, stroke, multiple sclerosis, shingles, and cancer treatments.

What causes neuropathic pain?

Patients may develop neuropathic pain due to various reasons. However, on a cellular level, an increased release of certain neurotransmitters signaling pain, combined with impaired nerve regulation of these signals, leads to the sensation of pain. In the spinal cord, the area interpreting painful signals is rearranged, resulting in the perception of pain without external stimulation. In the brain, the ability to block pain can be lost following an injury. Over time, further cellular damage occurs and the sense of pain persists.

Neuropathic pain is associated with diabetes, chronic alcohol intake, certain cancers, vitamin B deficiency, infections, other nerve-related diseases, toxins, and certain drugs.

What are the signs and symptoms of neuropathic pain?

The identification of neuropathic pain is challenging as few objective signs are present. Patients describe their symptoms using various descriptors like sharp, dull, hot, cold, sensitive, itchy, deep, stinging, burning, or others. Some patients may feel pain with light touch or pressure.

To assess pain intensity, different scales are used. Patients rate their pain based on visual scales or numeric graphs. Pain scales with pictures depicting various degrees of pain can be helpful when patients struggle to describe their pain.

QUESTION

How do doctors diagnose neuropathic pain?

The diagnosis of pain is based on further assessment of a patient’s history. If underlying nerve damage is suspected, evaluation of the nerves with testing may be necessary. Nerve conduction studies with electromyelography (NCS/EMG) are the most common way to evaluate nerve injuries. Clinical evaluation may reveal evidence of function loss, assess light touch, distinguish sharp from dull, discern temperature, and evaluate vibration. Clinical examination is followed by an electrodiagnostic study performed by specially trained neurologists and physiatrists.

If neuropathy is suspected, searching for reversible causes is necessary. This can include blood work for vitamin deficiencies or thyroid abnormalities and imaging studies to exclude structural lesions impacting the spinal cord. Depending on the results, the severity of neuropathy and pain can potentially be decreased. Unfortunately, in many conditions, good control of the underlying cause of neuropathy cannot reverse the neuropathy, as seen in patients with diabetic neuropathy.

In rare instances, evidence of changes in the skin and hair growth pattern in an affected area may be present, indicating the presence of neuropathic pain associated with complex regional pain syndrome.

What is the treatment for neuropathic pain?

Various medications have been used to treat neuropathic pain. Most of these medications are used off-label, meaning they were approved by the FDA to treat other conditions but have shown benefits in relieving neuropathic pain. Tricyclic antidepressants, such as amitriptyline, nortriptyline, and desipramine, have been prescribed for neuropathic pain control for many years. Other types of antidepressants and antiseizure medications have also been shown to provide relief. Medications applied directly to the skin, like lidocaine or capsaicin, can benefit some patients. The use of narcotic agents to treat chronic neuropathic pain is a topic of debate and not recommended without specific guidance.

Curing neuropathic pain depends on the underlying cause. If the cause is reversible, peripheral nerves may regenerate and pain will subside; however, this reduction in pain can take many months to years.

What is the prognosis for neuropathic pain?

Most patients with neuropathic pain can find some relief, even if their pain persists. Although neuropathic pain is not dangerous, it can negatively impact the quality of life. Patients may suffer from sleep deprivation, mood disorders, or be at risk of injury or infection due to lack of sensory feedback.

Is it possible to prevent neuropathic pain?

The best way to prevent neuropathic pain is to avoid developing neuropathy. Monitoring and modifying lifestyle choices like limiting tobacco and alcohol use, maintaining a healthy weight, and using good ergonomic form decrease the risk of developing neuropathy and potentially neuropathic pain.

References:

Magrinelli, F., et al. "Neuropathic pain: diagnosis and treatment." Practical Neurology 13.5 (2013): 292-307.

Marchettini, P., et al. "Painful peripheral neuropathies." Current Neuropharmacology 4.3 (2006): 175-181.

Mendell, J., et al. "Clinical practice. Painful sensory neuropathy." New England Journal of Medicine 348.13 (2003): 1243-1255.

O’Connor, A. and R. Dworkin. "Treatment of neuropathic pain: an overview of recent guidelines." The American Journal of Medicine 122.10 Suppl (2009): S22-S32.