ALLODYNIA: CAUSES, TYPES, DIAGNOSIS AND TREATMENT - NEUROPSYCHOLOGY - 2024

The allodynia is a condition caused by injury to the nerve endings in which severe pain to stimuli that are painless or pain do not produce a great extent under normal conditions are experienced.

People who suffer from allodynia feel pain from the brush of the wind, when changing clothes, being exposed to cold or heat, etc. It is one of the most unknown disorders within chronic pain and also one of the most difficult to address.

Pain is totally subjective, in addition to being dynamic and multiple. That is why we speak of the pain threshold. This means that when faced with certain stimuli, some people will feel more pain than others, and vice versa. In this case, patients suffer great pain in situations that are not painful or annoying at all compared to people who do not suffer from allodynia.

In the case of allodynia, the pain is residual. This means that people can continue to experience pain even after the painful stimulus has been withdrawn.

In general, pain is an adaptive mechanism, but in this case, being a chronic, continuous and unbearable pain, these people suffer emotional repercussions, such as anxiety and depression. In fact, it is estimated that around 85% of people who are diagnosed with allodynia use antidepressants.

Neuropathic pain has two characteristics: (1) pain occurs spontaneously, suddenly, and (2) hyperalgesia, which means that painful stimuli are perceived in an exacerbated way. That is, a lot of pain is felt from a stimulus that does not produce such magnitude in someone who does not suffer from neuropathic pain.

Causes

Allodynia belongs to the group of neuropathic pain that is characterized by being a form of pain produced by damage or changes in the information-transmission mechanism of the peripheral or central nervous system. In this case, the nerves send pain signals without there really being a real pain sensation or painful stimulus.

The main cause of allodynia is the existence of an imbalance in neurotransmitters. It can also be due to a failure of the nervous system (as we have seen before), when nociceptors (sensory pain receptors) do not work properly.

At other times, allodynia may be the result of another condition or pathology. In this case, it is known as secondary allodynia.

The frontal orbital accumbens-medial thalamus network is involved in the affective perception of pain. Regarding the posterior frontal cortex, it acts by controlling and modulating pain and, therefore, the degree of suffering.

Types

In the first place, we have to distinguish pathological and physiological allodynia. When we talk about pathological allodynia, we mean when there is no recent damage, injury or wound. This is what I have previously spoken of as neuropathic pain.

With regard to physiological allodynia, it is that which occurs when an area has been damaged and is in an active phase of repair. For example, the pain experienced in the scar after an operation. That is, there is a real cause of pain.

Next, we are going to see the different types of pathological allodynia. Despite how unknown it is, different types have been classified according to the stimulus that causes them:

Static mechanical allodynia

It occurs when experiencing pain from the application of a single stimulus or by light pressure. For example, like when someone takes us by the hand.

Dynamic mechanical allodynia

People suffer pain with the repeated application of gentle stimuli or a small touch. They experience great pain when touched, such as when a soft cotton ball is passed to them.

Rhermic allodynia

Pain is felt from the application of thermal stimuli, either hot or cold.

Secondary type

In some cases, allodynia is secondary in type. That is, it is a consequence of another disease. Allodynia may be caused by diabetes, nerve compression, vitamin B12 deficiency, migraine, etc. In these cases, the person may experience relief or the allodynia may disappear by treating the main condition.

Diagnosis

To diagnose allodynia, there is no specific test or examination that shows us the existence of the disorder.

In this case, as in other cases of neuropathic pain, we must base ourselves on the clinical history and physical examination; The differential diagnosis of other neuropathies must also be made. Tests or exams that are not really necessary should be avoided, thus reducing the stress that the person may experience before a test.

Therefore, personal history and medical history, previous and current treatments must be taken into account.

Among the tests that can be performed, by the different health specialists, we find the following:

• Semi-structured interview.
• Bedside examination.
• Laboratory exams.
• Pain questionnaires.
• Electrophysiological studies.
• Central and Autonomous Nervous System Exam.

Treatment

Currently, there is no treatment that will cure allodynia.

Drugs

Normally, from a medical point of view, the treatment of pain is treated through the administration of drugs. These drugs are usually non-opioid and opioid, depending on the discomfort caused by the pain in the patient. This type of treatment is not usually successful in the case of allodynia since we are faced with neuropathic pain.

Mixed combinations of local anesthetic drugs (such as ointments and patches) can be used in allodynia. Relief occurs locally, but the anesthetic is absorbed and its effects may contribute to the inhibition of central nervous system hyperexcitability. It is not advisable to abuse these remedies, since toxic concentrations can be reached in the nervous system.

Ketamine (dissociative anesthetic) and dextromethorphan (opiate) have been studied as antagonists of the N-methyl-D-aspartate receptor and have beneficial effects in cases of pain, such as allodynia.

Surgery

In extreme cases, when the pain is very intense and there is no feeling of relief, a surgical intervention can be performed in which some of the nerve connections to the pain are removed.

Therapy

On an emotional level, the intervention of the psychologist is very important, since people with this type of pathology often experience incomprehension on the part of their closest circle. Also, it can cause problems in the workplace, they see their abilities diminished, etc.

That is why it is important, at first, to re-adapt the person in the different contexts of his life and to promote that in all of them he feels understood.

Biofeedback

Biofeedback techniques are useful, which consists of, through the electrical activity of the brain, teaching the person to control brain waves, in order to adjust the mental state.

Coping strategies

Next, we are going to see a series of coping strategies that are used from psychology in the management of chronic pain. They can be used both in allodynia and in any other disorder or disease, whether physical or psychological, that causes any type of chronic pain.

It is important that they are conducted by a professional psychologist and that before using them, an evaluation of the previously used strategies is carried out.

Thought detection

It consists of (1st) realizing the thought of pain and (2nd) stopping that thought.

This training can be done at times when there is no pain, with the aim of practicing it. It is about cutting off the thought, another thought can be introduced, directing attention to another activity that keeps the patient in a state of alert.

Distraction techniques

It is about distracting thoughts and feelings related to pain. Attentional focus is shifted from an internal to an external locus of control (place of control). That is to say, it goes from depending on the individual himself to doing so on other variables.

* These first two techniques can be used together.

Control and scheduling of activities

It is about establishing a new routine, with new habits. The patient's habits are modified based on their activities, which generally revolve around pain.

To do this, at first, behaviors related to pain are recorded and the variables involved are analyzed. Then, those that are painful will be exchanged with new ones that are positive for you.

Relaxation training

This technique by itself will not eliminate pain. Its effect is to focus attention on something other than the pain itself. It will serve to counteract negative emotions (anger, hopelessness, helplessness) related to pain.

Currently, related to relaxation, more and more techniques such as meditation and mindfulness are used with great results.

Imagination techniques

They can be used with relaxation and consist of modifying certain thoughts through imagination.

Systematic desensitization

When a person experiences pain in a certain situation, they tend to avoid that circumstance again. Sometimes, these circumstances greatly limit the activity of the person, for this reason, the psychology professional will elaborate a series of preliminary steps (successive approximations) before exposing himself to that circumstance again.

Self-instructions and self-verbalizations

A person can become his own worst enemy if he does not stop sending negative messages. In this case they can be of the type: “I can't take it anymore”, “this pain will be able to me”, “since I experience pain I am no longer the same person”, etc. These messages sink in and, little by little, the person becomes more incapable and her spectrum of activity is reduced.

If these messages are exchanged for others of a positive kind, we will feel more capable. It's about being realistic, not fooling ourselves. For example, you can use this type of message: “it hurts, but today I am going to go out to do the shopping, I am not going to charge much. I will buy the most urgent and the day after tomorrow, I will go back to get the things that I need ”.

Discussion of irrational ideas (Ellis)

Human beings tend to have conversations with ourselves and, sometimes, irrational thoughts occur that can lead us to act or show feelings in an inappropriate way.

Through this technique, the therapist tries to actively and directly discuss these irrational beliefs and replace them with other types of thoughts and beliefs that are adaptive.

Regarding the treatment, we can conclude that, after a thorough evaluation of the patient's situation, drugs and psychological techniques should be used that serve to respond to all their symptoms.

The reviews and control by specialists should be active, giving the person a feeling of control over their pain and supporting them in managing it. For this, active listening is of vital importance.

References

1. CAMPOS KRAYCHETE, D; KIMIKO SAKATA, R. (2011). Painful peripheral neuropathies. Brazilian Journal of Anesthesiology 351 Vol. 61, No 5, September-October, 2011
2. CERVERÓ, F. (2000). Neuropathic pain: a scientific and therapeutic problem. Spanish Society of Pain Magazine 7: Suppl. II, 2-4, 2000.
3. The mind is wonderful. Allodynia: when caresses hurt. Website: lamenteesmaravillosa.com.
4. NeuroWikia, content portal in Neurology. Neurological pain Positive phenomena. neurowikia.es.
5. SaludMecidina.com. Allodynia, when even caresses hurt. Website: saludymedicinas.com.mx.
6. HEALTH (2011). Fibromyalgia Ministry of Health, Social Policy and Equality.