Astereognosia is the inability to recognize shapes by palpation with eyes closed. The cause is damage to the central nervous system, where tactile impressions are processed and made to be recognized. Astereognosia is causally untreatable in most cases and for this reason can usually be alleviated at best by targeted tactile training.
What is astereognosia?
Humans are capable of recognizing things by mere touch. Even with eyes closed, the shape and consistency of what is touched tells him enough about the object property. Thus, in addition to touch recognition, the sense of touch is also responsible for active tactile exploration of things with eyes closed. In addition to the structures of the sense of touch, the associative centers and memory sections of the brain play a role in object recognition. What is touched is compared with previous touch experiences and thus ideally recognized. The ability to recognize objects by means of active exploration is called stereognosia. If there is an inability in this respect, it is called astereognosia. Patients with this disease symptom can no longer recognize things by mere touch. The terms tactile paralysis, tactile agnosia and stereoagnosia are used synonymously with the disease name. Astereognosia belongs to the agnosias. As such, neuropsychological disorders following cerebral unilateral or bilateral cortical or subcortical lesions that impair central sensory processing are known.
Causes
The ability to recognize shapes by mere touch is located in the primary somatosensitive cortex of the brain. This is a defined portion of the cerebral cortex for central processing of haptic perception. The incoming information originates from the receptors of the skin or the receptors inside the body. In addition to touch, pressure sensations, vibrations and temperatures, pain sensations are also partially processed in the somatosensory cortex. The somatosensory cortex is the end of the neolemniscus and is divided into primary sensitive areas in terms of Brodmann areas 1, 2 and 3. In addition, it contains the secondary-sensitive association areas in terms of areas 40 and 43. Most of the primary-sensitive cortex is located on the postcentral gyrus behind the central furrow. The secondary portion connects posteriorly inferiorly. In most cases, astereognosia is due to damage to the brain in the above areas. Especially often, the symptom occurs after damage to the secondary associative areas. Such damage can be traumatic, but it can also be caused by neurological diseases such as multiple sclerosis. Tumor diseases or strokes and degenerative changes are also possible causes of the lesions. Damage to the parietal association cortex in the nonlanguage-dominant cerebral hemisphere after a stroke is sometimes the most common cause.
Symptoms, complaints, and signs
In patients of astereognosia, the receptors of the sense of touch do perceive primary sensory impressions. Thus, sensation as the first step of perception is not disturbed. A disturbance is present exclusively in the central processing of the sensory impressions. The patients’ sense of sight functions perfectly in most cases. Therefore, they can still name objects and shapes despite astereognosia as long as they keep their eyes open. However, when they close their eyes and are supposed to match shapes by the mere tactile impression, they are unable to do so. This symptom of a central lesion rarely occurs in isolation. In most cases, the symptom of astereognosia is associated with characteristic symptoms of the respective lesion. Accordingly, some of the patients additionally suffer from disorders of vibratory sensation. Others suffer from additional disorders of proprioception or general touch sensitivity. Just as often, additional disturbances of thermoception or pain sensation manifest themselves. Exactly which symptoms occur in individual cases depends on the localization of the respective damage.
Diagnosis
Diagnosis of astereognosia is primarily made anamnetically or by palpation test. Imaging of the brain allows closer classification of the inability to recognize objects and enables localization to a specific area of the brain.To establish the diagnosis, a differential diagnostic differentiation from sensory disturbances and cognitive impairments of other kinds is necessary. Often, diagnosis of the causative brain lesion occurs before symptomatic diagnosis of astereognosia.
Complications
Astereognosia does not result in physical complications. However, it can severely limit the life of the affected person and usually cannot be treated. Most affected individuals can recognize all other sensory impressions without problems or difficulty, but no shapes can be recognized. Astereognosia can cause psychological problems and lowered self-esteem. Especially children can be disadvantaged if they are bullied at a young age due to astereognosia. Most people also experience disturbances in the sensations of warmth and cold. Injuries can occur because extreme and dangerous situations cannot be assessed correctly. Everyday life is also made more difficult by astereognosia, which can lead to severe orientation problems, especially in blind people. Treatment is not possible. However, the skills can be trained and practiced so that astereognosia can be severely limited. This is especially the case if astereognosia has developed after a stroke. In this case, no complications occur, but it cannot be predicted whether the astereognosia will completely regress. In the case of inflammation in the brain, surgical interventions can be performed, which likewise lead to a positive course of the disease.
When should you see a doctor?
Recognition of the structures of objects or surfaces without the involvement of the eyes requires that the primary stimuli of various tactile sensors in the skin, as well as additionally other haptic stimuli such as pressure and vibration sensations and also pain stimuli, are correctly detected by the sensors and sent as impulses to brain areas of the somatosensory cortex. There, the stimuli are combined in a complex processing process to form an overall impression that allows us to recognize the shape and texture of an object even without eye contact. The characteristic of astereognosia is that the sensory stimuli are correctly sent to the brain, but the responsible centers are not able to process the incoming stimuli into an overall picture. Most often, astereognosia is acquired as a result of an accident with brain lesions, a stroke, or tumors in the CNS due to spatial stress. If symptoms suggestive of astereognosia occur, it is imperative to seek medical advice from an experienced specialist to determine the extent of brain dysfunction. Based on the diagnosis, an exercise program can be devised to help reduce the effects of the neurological deficits. There is no drug therapy or other therapy that could cure the condition. Interestingly, even if the sense of touch is completely intact, the form impression strictly follows the visual impression in case of conflict between the two impressions. For example, a straight bar appears to have a kink when viewed through a prism. The sense of touch erroneously reports this kink as well, an impression that immediately disappears when the eyes are closed.
Treatment and therapy
Causative therapy is not available for astereognosia in most cases. For causative therapy, the specific cause would have to be eliminated. For all lesions of the central nervous system, complete mostly elimination is not possible. Central nervous tissue is not capable of complete regeneration. For example, if an inflammation of the brain has caused the symptom of astereognosia, the inflammation can be made to subside by cortisone administration, but scars remain in the inflamed area. These scars continue to impair the ability in the long term. However, there is usually no longer complete agnosia, but only a reduced ability to process the affected areas. Even after strokes and traumatic brain injuries, scars and thus impairments remain. In the case of tumors, the situation is somewhat different. In this case, complete removal of the tumor may serve as a causal therapy and fully restore the ability of stereognosia.Under certain circumstances, in addition to the therapy of the primary disease, training of the tactile ability can at least improve the existing astereognosia. Ideally, after targeted training, neighboring cells of the brain take over the responsibilities of the defective brain cells.
Prospect and prognosis
The prognosis for astereognosia is considered unfavorable under current scientific conditions. The disease cannot be treated with current medical options. Relief of symptoms is also not possible. The disorder results from damage to the cortical area. The tissue in the brain is considered unrepairable when damaged. Despite numerous efforts, scientists and researchers have not yet succeeded in curing defective brain tissue with drugs or surgical interventions. An exchange of the brain comparable to an organ transplantation is also impossible with the current possibilities. Although the efforts of the researchers are continuing, at present no positive healing prospect can be given to a patient with astereognosia. Furthermore, an increase in the existing symptoms is also not to be expected. The brain damage is not spreading according to the findings and treatment reports to date. The possibilities of self-help or alternative healing methods also do not lead to success in case of astereognosia. The organism cannot heal itself from its own forces for damages of the brain tissue. In addition, the prerequisites for an alternative natural healing method are also not present. Therefore, the goal of treatment is to optimize the quality of life under the given conditions. It is helpful to take advantage of psychotherapeutic accompaniment.
Prevention
Astereognosia can be prevented only to the extent that causative strokes, brain inflammation, and degenerative processes within the brain can be prevented.
Follow-up
As a rule, patients with astereognosia do not have any options for follow-up care. However, these are also not necessary, as the disease also cannot be fully treated and does not always need to be treated. The patient’s life expectancy is not negatively affected by astereognosia. However, the disease can negatively affect and complicate the life of the affected person. Treatment is usually based on the exact causes of astereognosia. In some cases, it may be useful to take medication to alleviate the symptoms. The patient is dependent on taking the medication regularly, and interactions with other medications should also be taken into account. If the astereognosia is caused by a tumor, it must be removed. Early removal of the tumor has a very positive effect on the further course of the disease and can prevent further complications. An examination for further tumors is also useful. It is not uncommon for those affected by astereognosia to also suffer from psychological complaints. In this case, contact with other sufferers of the disease can have a positive effect on the further course, as this leads to an exchange of information.
What you can do yourself
As a rule, the disorder cannot be treated. However, those affected can learn to cope better with their impairment and to master everyday life. Provided vision is not impaired and no other symptoms are added, adult patients usually have no problem coping with the challenges of daily life. In most cases, the social environment does not even notice the disorder. However, some sufferers are inhibited because of their condition. If these inhibitions impair the quality of life, the affected persons should seek therapeutic help. If not only the sense of touch is disturbed, but also other sensory perceptions such as the sense of pain or temperature, the risk of injuries and accidents in everyday life increases. Particularly when astereognosia and its accompanying symptoms first appear in adulthood, those affected must learn to actively prevent accidents. Gas stoves are then safer than electric stoves because the flame can be seen, while heat is not always perceived. There is also a risk of scalding when taking a bath or shower.Therefore, shower devices should be equipped with taps that allow the presetting of a certain temperature. The bath water should always be measured as a precaution. Provided that only the sense of touch is impaired, this can be trained, especially if the astereognosia was caused by a stroke. Affected persons should have a physiotherapist who has experience with the disease draw up an exercise plan. The sense of touch can be at least partially regained in this way.