Neuropathic pain: causes, symptoms and treatment

March 31, 2024

Feeling pain at some point is something that happens to everyone.

We give ourselves a blow, we cut ourselves or we just make a bad gesture and quickly our nervous system captures and informs that there is an injured tissue and causes us that undesirable and annoying aversive sensation that we call pain. Undesirable but adaptive, since it warns us that something is wrong and allows us to act to remedy it.

But nevertheless, sometimes the pain appears without a real problem and it stops having a feeling or, as it happens in people with neuropathic pain .

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Pain and its transmission

The sensation of pain is a mechanism of our organism, mainly somatosensory , which detects the presence of a stimulation or situation that is damaging or has the potential to damage our tissues. And it not only affects us physically, but also emotionally and mentally. The perception of pain allows us to launch a series of actions and behaviors that will make us move away from the harmful stimulus or prevent it from damaging us. It is therefore a mechanism of innate origin although modifiable through experience and habit that allows our survival and prevents our death and incapacitation.

So, although we know pain first through the subjective experience that it produces, we must bear in mind that this phenomenon it is not something that only exists for us, in our imagination . In fact, as much as the first ones interested in not suffering pain are ourselves, it comes from a material process that can be investigated objectively through observation and measurement. Thanks to this we know certain objective and verifiable aspects about pain in general and neuropathic pain in particular; otherwise, we could not say anything about it.

What we know about this physiological and psychological process

At the neurological level, pain is experienced when a series of receptors present in the vast majority of our body are activated, the nociceptors, which, in the event of breakage, impingement or intense pressure, activate and send signals to the nervous system .

Specifically, the signal is sent through fibers and ganglia to the posterior horn of the spinal cord, with which they communicate through the use of glutamate and that known as substance P. The marrow will cause an immediate response in the form of reflex while sending the sign of pain to the brain (the spinothalamic beam being the best known route).

However, not always that there is an injury we will feel pain, having a circuit of nerve fibers that can inhibit the transmission of signals. This circuit is visible when the level of pain decreases when we rub a hit area or its surroundings. Depending on whether the excitatory or inhibitory pathways of pain are activated, we will eventually perceive a painful sensation. In addition, once the lesion is perceived, the brain proceeds to send endorphins that counteract the painful perception, allowing us to ignore the pain and focus on fighting or escaping from the stimulus.

This would be the process that would normally lead to the perception of pain, but as we said there are people who feel pain without there being any stimulus that should produce it, people suffering from neuropathic pain . What happens in these cases?

Neuropathic pain: what is it and how is it produced?

It is known as neuropathic pain to the type of pain that appears in situations and contexts in which there is no sufficiently intense or harmful stimulation for pain perceptions to appear. Stimuli that normally do not cause pain produce it. Thus, small frictions and even some generally pleasant contacts such as a caress or a kiss can become a real torment for people with this type of problem, since their nervous systems perceive them as something extremely painful .

The type of pain experienced can vary greatly depending on the cause of the damage and the level of involvement and reactivity of the nerve pathways. It is very frequent to appear in the form of burning pain, that is to say as if a burn was suffered, or in the form of punctures or punctures. In some cases numbness of the area may also appear. The pains can be maintained continuously over time or may appear and disappear.

Neuropathic pain poses serious difficulties for those who suffer from it, maintaining a high level of discomfort and frustration. Many people with this type of pain may end up suffering from anxiety disorders or severe depression, in some cases with suicidal ideation. It is not uncommon to avoid as much as possible leaving your home, physical contact with other people and actively limit your social, family and work life, being a very disabling condition. It also causes sleep problems, which causes that in many cases there is great fatigue and stress .

The reason for this disorder is the presence of damage to the somatosensory system, with the nerve bundles that transmit the somesthetic information to the brain being damaged. This damage can be located both at the level of the central nervous system and peripheral. As a consequence, neurons that transmit pain become hyperexcitable and react with a lesser amount of stimulation, and sometimes even without real stimulation.

Causes

The damage to the nerve pathways that ends up causing neuropathic pain can come from a wide range of disorders and conditions, neuropathic pain receiving different names according to their cause.

1. Neurodegenerative diseases

When neuropathic pain occurs due to damage to the nerve pathways it is logical to think that disorders in which there is an alteration or degeneration of the nerves This type of problem may appear. Thus, in diseases such as multiple sclerosis and in some dementing processes it is possible that pain appears linked to the degeneration of the nerves.

2. Diabetes mellitus

People with diabetes mellitus can develop nerve pathways over time , by weakening nerves due to vascular alterations or lack or excess of blood glucose. In this case we would be talking about painful diabetic neuropathies. The most common is diabetic peripheral neuropathy, in which there are paresthesias, sensations of burning or cooling, loss of sensation and pain in the extremities.

3. Poor nutrition

The absence of sufficient nutrients in the body can cause nerve cells to be altered and weaken , causing in the long run the peripheral nerves to end up reacting abnormally.

4. Viral infections: Herpes and HIV

Some viral infections can cause an alteration in nerve pathways that can cause neuropathic pain . It is common in the case of the herpes zoster virus, in which pain usually appears both in the torso and in the face.

Also in the case of acquired immunodeficiency syndrome or AIDS, produced by HIV, may appear a degeneration of nerve tissue that can cause pain of this type appear.

5. Tumors

Some cancers and tumors can damage nerve pathways , both by direct effect of the tumor and by producing a possible impingement of the fibers that drive the painful information.

6. Injuries, hemorrhages and ischemic accidents

Whether due to a partial or complete asphyxia of the neurons or to their clamping with other parts of the organism, cerebrovascular accidents and traumatic brain injuries they can be, in many cases, the origin of neuropathic pains.

Treatments

The treatment of neuropathic pain is complex and requires a multidisciplinary approach . It is a chronic disorder, although it is possible to reduce the patient's pain and greatly improve their quality of life.

Sometimes the cause of the pain can be treated in a more or less direct way and prevent permanent damage to the nervous tissue, as in some cases of diabetes. Some of the treatments contemplated are the following.

1. Antidepressants

The use of antidepressants is frequent to alleviate both the level of pain and the psychological effects of it. However, they should be used with caution, since it is intended to reduce the level of pain and not sedate the patient .

In the case of antidepressants, it has been proven that those that have an effect that allows regulating the level of pain are those that affect both serotonin and norepinephrine, with which SNRIs such as duloxatin are usually used with some success. They seem to work especially well in some cases of neuropathic pain derived from diabetes.

2. Anticonvulsants

The drugs used to treat epilepsy have also been shown to be very useful against neuropathic pain, both in cases derived from sclerosis and viral infections, diabetes or others. For example, Carbamazepine is used as the treatment of choice for trigeminal neuralgia , one of the most painful disorders that affects the nerves of the face.

3. Opioids and cannabinoids

As with the pain produced by some types of cancer, substances such as morphine have been used in the case of neuropathic pain, marijuana or other derivatives of opium and cannabis to help reduce and manage the level of pain .

4. Other substances: Capsaicin

In addition to those already mentioned, it has been found that other substances such as capsaicin can help fight the pains , either orally or applied at cutaneous or subcutaneous level.

5. Transcranial magnetic stimulation

The stimulation of nerve centers and the somatic system has been shown to reduce the pain level of patients with this problem.

6. Surgery

If the cause of the pain is localized and its implementation is viable, corrective surgery can be applied to help improve and correct the problem. As a last resort, ablation of damaged nerve tissue could be performed .

In addition, at a medical level it is possible to block the damaged nerve pathway, either by drug infiltration or by radiofrequency.

7. Psychotherapy

Neuropathic pain often causes patients to exhibit maladaptive coping strategies to face the day-to-day events, as well as anxiety and depression problems. Psychological treatment and psychotherapy can contribute to a large extent through programs and therapies that help cope and learn how to manage pain, establish routines and appropriate action strategies and facilitate the expression and communication of emotions and sensations that their state produces.

8. Physiotherapy

The rehabilitation and physical conditioning of the patient can help to become less sensitive to pain and improve their quality of life, being able to reduce the intensity and frequency of the pains and improving their condition both physically and mentally.

Bibliographic references:

Finnerup, N.N. et al. (2007). An evidence based algorithm for the treatment of neurophatic pain. Medscape Gen. Med; 9 (2): 36

O'Connor, A.B. & Dworkin, R.H. (2009). Evidence-based treatment of chronic neuropathic pain using nonopioid pharmacotherapy. Continuum Lifelong Learning Neurol; 15 (5): 70-83.