Allodynia – Causes, Treatment & Prevention

In medicine, allodynia refers to a sensation of pain that is caused by stimuli that do not cause pain under normal circumstances . In the context of polyneuropathy, for example, it is possible that clothing lying on the skin is perceived as painful. In addition, allodynia occurs as an accompanying symptom in numerous neurological diseases.

In addition, allodynia sometimes occurs in pediatrics. Here it occurs more often in premature babies who have been treated in intensive care. In these cases, allodynia is caused by a high frequency of treatments and mostly inadequate analgesia. A more common example of allodynia is the sensitivity to touch that occurs with sunburn .

Basically, allodynia is associated with neuropathic pain and its expression. The sensory cells in the human skin and mucous membrane are usually the places where stimuli are first perceived. These include, for example, the so-called nociceptors , which are particularly responsible for painful stimuli. Because the nociceptors are the free endings of the nerves of the sensitive neurons in the spinal cord .

They are found in all tissues in the body that are sensitive to pain. The pain receptors report the stimuli to the central nervous system . These stimuli are, for example, surface pain, deep pain affecting the joints and muscles , and pain originating from the internal organs. When a certain stimulus intensity is reached, a so-called action potential is generated at the nociceptors. This is reported to the spinal cord as a neuronal excitation and is then passed on to the brain . There the stimulus finally reaches consciousness.

Causes

There are many possible causes of allodynia. The trigger for the disease is usually either in the central or in the peripheral nervous system . In addition, the psyche of the affected patient may also be responsible for the allodynia. Basically, the therapy of allodynia depends on the underlying cause. In most cases, the cause of allodynia lies in diseased nerves or the areas of skin that they supply, which in many cases are already damaged.

Sometimes the polyneuropathies suffered trigger a sudden C-nociceptor activity, which can cause allodynia. In the case of polyneuropathy, nerve fibers are lost over the long term. The situation is similar with allodynia, in which segmental tissue losses occur in the so-called posterior horn of the spinal cord. The cause can also be found in part, for example, in trigeminal neuralgia, whereby unprotected nerve fibers are in the immediate vicinity and thus lower the stimulus threshold. However, there are also psychological factors that can trigger pain. For example, fears or a general tendency to somatize promote certain hypersensitivities.

Basically, the stimulus threshold that is necessary for the development of the action potential varies from person to person. Every person has an individual pain threshold. It should be noted, however, that a low pain threshold does not necessarily have to mean illness. However, if the nociceptors trigger a corresponding action potential even with pleasant touch stimuli and report pain in the brain, a disease value can be assumed. In such cases, allodynia is present. This is characterized by the fact that pain is felt even though the responsible stimuli are harmless and generally tolerated.

Diseases

• polyneuropathy

• neurological diseases

• Trigeminusneuralgie

• anxiety disorders

• nerve injury

When to the doctor?

If the first symptoms and signs of allodynia appear, a doctor should be consulted. The disease leads to a severe impairment of the quality of life and can no longer be improved by the person affected without medical care. There is no reason to worry if you experience slight pain or are already familiar with the sensitivity of the stimulus reaction to pain and temperature influences. This is not a condition of concern that requires further investigation.

Allodynia is characterized by the fact that the affected person feels at the mercy of a stronger perception of pain than is normally the case. Since the experience of pain is often not taken seriously by people from the social environment, the person affected must find the courage on their own and nevertheless report the symptoms to a doctor.

This often requires an overcoming, which is important. In a self-test, those affected can quickly determine whether the pain is worse than they have perceived it in the course of their life. Allodynia is caused by hypersensitivity of the nerve fibers . Without an adequate examination, it is not possible to distinguish these from serious damage to the nerve. Since a damaged nerve, if left untreated, will lead to the death of other nerve fibers, it is advisable to see your doctor in good time.

Diagnosis and course

Various examination methods can be used to diagnose allodynia. Basically, allodynias are diagnosed in neurology. The so-called provocation test is used to make the diagnosis. The doctor exerts various stimuli on the skin of the affected person. For example, toothpicks, fingers or a metal roller with different temperatures are used. The patient must report any pain sensations that occur and describe their intensity.

Following the diagnosis of allodynia, diagnostic measures are taken to determine the underlying disease. If imaging methods of the peripheral and central nervous system remain without findings, the allodynia probably has a psychological cause. In the case of allodynia, the prognosis is highly dependent on the respective patient and the individual characteristics and severity of the disease as well as the underlying disease. In general, centrally mediated allodynia tend to have an unfavorable prognosis. If the causes are psychological, the prognosis is relatively good.

Complications

Complications of allodynia include deterioration in the sufferer’s mental health if left untreated. This can cause illnesses such as anxiety or panic . The patient increasingly begins to systematically avoid many everyday processes. This avoidance strategy can lead to a burden for him and his immediate social environment. Interpersonal conflicts in coping with everyday life can arise.

Due to the pain, allodynia is associated with a restriction in one’s own lifestyle. Familiar activities can no longer be carried out. Depending on your career choice and qualifications, this can result in disability. In addition, compensatory activities in leisure time can no longer be pursued. Many sufferers suffer from the fact that they constantly have to deal with avoiding the pain. The persistent thoughts can cause headaches and a feeling of being overwhelmed.

It can happen that new pain occurs as a result of the sensitization that takes place in dealing with everyday situations. In addition, there is a risk that an existing pain experience will become chronic. If allodynia persists, the general well-being of the affected person progressively deteriorates. The mental state is permanently reduced and, if the condition persists for a longer period of time, leads to further physical complaints. There is a possibility of developing depression. Lack of drive and apathy often develop.

Treatment and therapy

A physically altered sensation of pain, as occurs in the context of allodynia, can only be treated with limitations. In principle, therapeutic measures are always carried out with regard to the underlying cause. In the case of mentally conditioned allodynia, adequate psychotherapy or general psychological support can be considered. Psychological therapy is possible in those patients suffering from other forms of allodynia. The affected persons learn to deal better with the changed sensitivity to pain. If the allodynia is based on organic causes such as an injury to the nerve tissue, the damage is irreparable in the majority of cases. This applies in particular to centrally mediated allodynia.

If the primary causes are treated, an improvement in the symptoms is possible. However, in most cases, the symptoms do not go away completely. With regard to organic causes, there are observations that patients have been able to normalize their pain threshold by exposing themselves to strong pain stimuli. This sometimes results in a habituation effect and the allodynia improves.

Outlook and prognosis

The prognosis of allodynia depends on the diagnosis. If there are psychogenic diseases as the cause, they are usually treated with various psychotherapies. Over a longer period of time, the patient gradually learns how to deal better with the pain experience in everyday life. The focus of perception can be changed. Using methods of conditioning, an improvement in the experience of pain can be brought about. The organism accumulates less stress hormones in occurring situations, so that an alleviation of the emotional experience is brought about. With these therapies, eliminating the pain is less important. More attention is paid to processes of the organism that take place concomitantly and cause reinforcement.

In some cases, the experience of pain is already initiated when imagining a situation and is experienced as agonizing. This process should be interrupted therapeutically. In the experience of pain, habituation effects occur, which can cause an alleviation, but also an aggravation of perception and thus the actual pain experience. If psychogenic causes can be ruled out, relief can usually be achieved with medication. Finding out the underlying disease is an important prerequisite for this. Once it has been corrected and there are no genetic defects, allodynia usually disappears completely. In the case of congenital causes, pain relief is usually only possible through long-term administration of medication.

Prevention

According to the current state of knowledge, there are no concrete measures to prevent allodynia. Only damage to the nervous system can be prevented in order to reduce the risk of centrally or peripherally mediated allodynia.