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

We bump, cut ourselves or simply make a bad gesture and quickly our nervous system picks up and reports that there is injured tissue and causes us that undesirable and annoying aversive sensation we call pain. Undesirable but adaptive, since it warns us that something is wrong and allows us to act to remedy it.

However, sometimes the pain appears without there being a real problem and stops having a feeling or, as in people with neuropathic pain .

Pain and its transmission

The sensation of pain is a mechanism in our organism, mainly somatosensory , that detects the presence of a stimulation or situation that is damaging or has the potential to damage our tissues. And not only does it affect us on a physical level, but also on an emotional and mental level. The perception of pain allows us to set in motion a series of actions and behaviours that will make us move away from the harmful stimulus or prevent it from damaging us. It is therefore a mechanism of innate origin but modifiable through experience and habit that allows our survival and prevents our death and disability.

Therefore, although we know pain primarily through the subjective experience it produces, we must keep in mind that this phenomenon is not something that only exists for us, in our imagination . In fact, as much as we are the first ones interested in not suffering pain, it comes from a material process that can be objectively investigated 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 a neurological level, pain is experienced when a series of receptors present in the vast majority of our body are activated , the nociceptors, which when broken, pinched or under intense pressure are activated and send signals to the nervous system .

Specifically, the signal is sent through fibers and nodes to the posterior shaft of the spinal cord, with which they communicate through the use of glutamate and the substance known as substance P. The cord will provoke an immediate reflex response while sending the pain signal to the brain (the most known route being the spinalothalamic bundle).

However, not every time there is an injury we will feel pain, there being 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 beaten area or its surroundings. Depending on whether or not the excitatory or inhibitory pain pathways are activated, we will end up perceiving a painful sensation. In addition, once the injury 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 the stimulus.

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

Neuropathic pain: what is it and how does it occur?

Neuropathic pain is the type of pain that appears in situations and contexts where there is not enough intense or harmful stimulation for pain perceptions to appear. Stimuli that do not normally 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 often appears as a burning pain, that is to say, as if you were suffering from a burn, or in the form of pricks or punctures. In some cases, numbness of the area may also appear. The pains can be maintained continuously over time or appear and disappear.

Neuropathic pain presents serious difficulties for those who suffer 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 for them to avoid leaving their home, avoid physical contact with others and actively limit their social, family and work life, a very disabling condition. It also produces sleep problems, which in many cases leads to great fatigue and stress .

The reason for this disorder is the presence of a damage in the somatosensory system, being damaged the nervous beams that transmit the somnesthetic information to the brain. This damage can be localized to both the central and peripheral nervous system. As a consequence, the neurons that transmit pain become hyper-excitable and react with a lesser amount of stimulation, and sometimes even without any 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, with neuropathic pain being given different names depending on its cause.

1. Neurodegenerative diseases

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

2. Diabetes mellitus

People who suffer from diabetes mellitus may develop alterations in the nerve pathways over time , as the nerves are weakened as a result of vascular alterations or the lack or excess of glucose in the blood. In this case we would be talking about painful diabetic neuropathies. The most common is diabetic peripheral neuropathy, in which there are paresthesias, burning or cooling sensations, loss of sensation and pain in the extremities.

3. Poor nutrition

The lack of sufficient nutrients in the body can cause nerve cells to be altered and weakened , eventually causing the peripheral nerves to end up reacting abnormally.

4. Viral infections: Herpes and HIV

Some viral infections can cause a disturbance in the nerve pathways that can lead to neuropathic pain . This is common with the herpes zoster virus, where pain often appears in both the torso and face.

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

5. Tumors

Some cancers and tumours can damage the nerve pathways , both by the direct effect of the tumour and by producing a possible pinching of the fibres that carry the painful information.

6. Trauma, bleeding and ischemic accidents

Whether due to a partial or complete asphyxiation of the neurons or to their pinching with other parts of the body, strokes and head injuries can in many cases be the source of neuropathic pain.

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 reason for the pain can be treated more or less directly and permanent damage to the nerve tissue can be prevented, as in some cases of diabetes. Some of the treatments considered are as follows.

1. Antidepressants

The use of antidepressants is common to alleviate both the level of pain and the psychological effects of pain. However, they should be used with caution, as is intended to decrease the level of pain and not to sedate the patient .

In the case of antidepressants, it has been found that those with a pain-regulating effect are those that affect both serotonin and noradrenaline, so SNRIs such as duloxatin are often used with some success. They seem to work especially well in some cases of neuropathic pain from diabetes.

2. Anticonvulsants

Medications 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 affecting the nerves of the face.

3. Opioids and cannabinoids

As with the pain produced by some types of cancer, in the case of neuropathic pain, substances such as morphine, marijuana or other opium and cannabis derivatives have been used 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 combat pain , either orally or applied at a cutaneous or subcutaneous level.

5. Transcranial magnetic stimulation

Stimulation of the nerve centres and the somatic system has been shown to reduce the level of pain of patients with this problem.

6. Surgery

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

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

7. Psychotherapy

Neuropathic pain often causes patients to present with maladaptive coping strategies to deal with everyday events, as well as problems of anxiety and depression. Psychological treatment and psychotherapy can contribute greatly through programs and therapies that help to confront and learn how to manage pain, establish appropriate routines and strategies of action and facilitate the expression and communication of emotions and sensations produced by their state.

8. Physiotherapy

Rehabilitation and physical conditioning of the patient can help to make him/her less sensitive to pain and improve his/her quality of life, being able to reduce the intensity and frequency of the pains and improving his/her condition both on a physical and a psychological level.

Bibliographic references:

  • Finnerup, N.N. et al. An evidence based algorithm for the treatment of neurophatic pain. 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.
  • Perez, I. and Ayuga, F. (n.d.) Neuropathic pain. Neurology Service of the Hospital Virgen de la Salud in Toledo. SESCAM. Toledo.
  • Valverde, J.A. (2012). Recommendations for pharmacological treatment of neuropathic pain. Neuroeje, 25 (2).