Allodynia

At Allodynia touch stimuli or temperature stimuli are perceived as unusually painful. The cause can lie in the peripheral and central nervous system or in the patient's psyche. Treatment depends on the primary cause.

What is allodynia?

Consult a doctor if there are signs of irritation to the nerves or hypersensitivity to pain and temperature associated with more than normal pain.
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Allodynia is associated with the expression of neuropathic pain. So-called sensory cells are located in the human skin and in the mucous membranes and are the first point of all perception. They include the nociceptors, which are accessible to painful stimuli. Nociceptors are free nerve endings of the sensitive spinal cord neurons and occur in all pain-sensitive tissues in the body.

The pain receptors report to the central nervous system surface pain, pain in the internal organs and deep pain in the sense of muscle and joint pain. From a certain stimulus intensity in their receptive field, nociceptors form an action potential that travels in the form of neuronal excitation via the spinal cord into the brain and reaches consciousness there.

The stimulus threshold for the formation of the action potential differs from person to person. Hence the statement that everyone has a different pain threshold. A moderately low pain threshold does not necessarily have to be associated with disease value. If, however, the nociceptors already generate action potential with pleasant touch stimuli and thus report pain, we are talking about disease value.

This phenomenon corresponds to allodynia and describes pain that is caused by harmless, generally tolerated stimuli. In addition, hyperalgesia is related to allodynia.

causes

The cause of allodynia usually lies in diseased nerves and the often previously damaged skin areas they supply. In the case of nerve damage, physical causes of allodynia are mentioned. Often in this context, the patients have suffered polyneuropathies in the past that activated spontaneous C-nociceptor activity.

The chronic loss of nerve fibers in the context of polyneuropathy is related to this phenomenon. In this sense, neuropathic pain syndrome is also characterized by allodynia. In addition, allodynia can be associated with segmental tissue loss in the posterior horn of the spinal cord.

The cause can also be trigeminal neuralgia, in which unprotected nerve fibers are in the immediate vicinity and lower the stimulus threshold via ephaptic neurotransmission. However, psychological factors can also play a role in the processes that trigger pain.

For example, fears and tendencies towards somatization favor any hypersensitivity. Depending on its location in the nervous system, allodynia is referred to as peripheral (primary) or central (secondary). Centrally mediated allodynia is often preceded by a stroke or a disease such as multiple sclerosis.

Patients with allodynia perceive painless contact and temperature stimuli as painful. Depending on the symptoms, allodynia is divided into subgroups:

• A mechanically dynamic allodynia is when a slight contact stimulus on the skin triggers pain, for example the stimulus of a cotton swab. The pain is characterized as stabbing or burning and can spread beyond the point of contact. A mechanically static allodynia leads to a sensation of pain when light pressure is applied to a certain skin area. A light finger pressure, for example, triggers dull pain.

• Mechanical pinprick allodynia is hyperalgesia. Patients with this form of allodynia perceive lightly stabbing touch stimuli on the skin as excessively strong, spreading pain, such as touching a toothpick.

• Cold allodynias are also hyperalgesia and easily intensify painful cold stimuli into more severe skin pain.

• The opposite phenomenon are heat allodynias, in which there is an over-sensitivity to heat pain and leads to burning sensations of temperature.

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Diseases with this symptom

• Polyneuropathy
• Pain syndrome
• Trigeminal neuralgia

• stroke
• CRPS
• Sudeck's disease

• multiple sclerosis
• Shingles
• Post-Disectomy Syndrome

Diagnosis & course

Allodynia are determined within neurological diagnostics. The provocation test is used to make a diagnosis. The examiner applies various types of stimuli to the patient's skin. To do this, he uses aids such as a toothpick, a cold and a warm metal roller or his own finger. The patient is asked to report and describe the pain sensation.

The diagnosis of allodynia is followed by a detailed diagnosis of the underlying disease. If imaging of the central and peripheral nervous system remains normal, there is likely a psychological cause for allodynia. The patient's prognosis depends on the primary cause. Centrally mediated allodynia has the worst prognosis. Psychological causes are usually best eliminated.

Complications

Various psychological side effects can occur in the context of allodynia. It can also lead to pronounced avoidance behavior on the part of the person concerned. So it is quite understandable that all situations that cause pain are avoided. However, this behavior does not make sense as it can ultimately lead to isolation of the person concerned. Activities that are normally performed with pleasure can no longer be perceived, as they are associated with pain.

Furthermore, some psychological side effects of allodynia are definitely possible. As part of allodynia, chronic pain can develop or arise. The patient is then permanently tormented by pain that is triggered by stimuli that normally do not lead to a pain sensation. If this fact lasts longer, it can trigger psychological reactions, for example a depressive episode. The avoidance behavior mentioned above, in combination with the chronic pain, can lead to a worsening of the psychological symptoms.

In addition to depression, anxiety can also occur. It can therefore be clearly seen that allodynia can lead to a whole range of other symptoms, some of which are mutually reinforcing. An important part of the therapy of allodynia is preventing the development of chronic pain and preventing psychological consequences. If this has already occurred, therapy using a combination of analgesia and psychotherapy is advisable.

When should you go to the doctor?

Consult a doctor if there are signs of irritation to the nerves or hypersensitivity to pain and temperature associated with more than normal pain. A slight or familiar sensation of pain is usually of little concern. This pain is characterized by the fact that it disappears again quickly and there are no further impairments. In contrast, severe pain indicates that one or more nerve fibers have been destroyed.

Self-tests can be done quickly by applying pressure to the skin. Since an untreated nerve can lead to the death of further nerve fibers, a medical examination should be clarified. Allodynia can have several causes. Not all can be classified as serious. Nevertheless, more details about the severity and the chances of recovery can only be said about a clarification and determination of the origin. The longer it takes to see a doctor or to start treatment, the further the damage can progress.

It also increases the risk of irreparable damage. Since psychological concomitant symptoms such as anxiety or depression can occur in addition to allodynia, a visit to the doctor is essential if the pain persists. Alternatively, the likelihood increases that the distinctions accompanying an allodynia can only be eliminated with lengthy therapies or that chronic consequences arise.

Doctors & therapists in your area

Treatment & Therapy

Physically changed pain sensations can only be treated to a limited extent. The cause determines the approach. Psychologically conditioned allodynias, for example, are dealt with with psychological support. Psychological support can also be useful for other forms of allodynia, so that the patient can better deal with his altered sensitivity to pain.

With all organic causes such as damage to nerve tissue, the damage is usually considered irreparable. This is especially true for centrally mediated allodynias. Treating the primary cause can lead to an improvement in the symptoms, but often does not completely subside. Pain therapies can be useful in this context, for example the implantation of a pump with pain reliever medication.

In some cases, for organic causes, a return to normalization of the pain threshold was reported after the patients had actually exposed themselves to strong pain stimuli. Even after regular exposure to slight, but severe pain, an adaptation or habituation effect and thus an improvement in allodynia could sometimes be brought about.

Outlook & forecast

In many cases, allodynia severely restricts the patient's life. Intimate contacts in particular are restricted, which can lead to problems with the partner. A doctor can usually make a diagnosis and determine whether the allodynia is caused by physical and mental illness. If the cause is psychological, the symptom is treated by a psychologist. The further course depends strongly on the psychological state of the patient.

Allodynia often leads to slightly aggressive behavior on the part of the patient, which is why they withdraw and isolate themselves socially. In addition to the actual pain caused by the illness, depression or anxiety often occur.

Targeted treatment by the doctor is not possible because the doctor cannot understand exactly how the pain arises. However, pain therapies can be helpful and greatly reduce the symptom. Painkillers can also be taken temporarily. However, long-term use should be avoided. Most patients also adapt to the pain. As a result, they no longer react as strongly to real pain as healthy people. This can be dangerous in some situations.

To prevent the symptom, damage to the nervous system should be avoided. Above all, this includes excessive consumption of alcohol and other drugs.

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prevention

Peripherally and centrally mediated allodynia can only be prevented to the extent that damage to the nervous system can be prevented. Mentally mediated allodynias can be prevented by promptly dealing with painful events and fears.

You can do that yourself

Allodynias, which are mainly psychological, can have a positive effect on those affected in various ways. Strategies and methods learned in appropriate therapies can be easily integrated into everyday life. Body-oriented relaxation methods, hobbies, conversations, pleasure training, careful desensitization instead of avoidance, adapted exercise in the fresh air and sufficiently long regeneration phases help against increased self-observation and focus on the pain.

Self-help measures are often ineffective in the case of physiologically justified allodynia. Participating in social life despite pain protects against loneliness and diverts the focus from one's own body to the outside world. Affected people make it easier for their relatives and friends to deal with the often difficult to understand reactions to affection and body contact by involving them in the psycho-educational process. In self-help groups they can address worries and needs and at the same time counteract social withdrawal and isolation. Participating in discussions in online forums or documenting their own experiences in diaries or blogs also helps many pain patients to cope with their illness.

The aim of supportive self-therapy should be to learn healthy withdrawal and self-protection behavior instead of an illness-preserving avoidance strategy. Particular attention should be paid to an adapted intake of painkillers, since an incorrect, too low or too high dosage is counterproductive. Despite the lack of evidence, complementary methods can also be helpful in individual cases.