Agnosia is a violation of the recognition of visual, auditory or tactile sensations during the normal functioning of the perceiving apparatus. According to the localization of the cerebral cortex lesion, the condition is characterized by a lack of understanding of what is seen, heard, unrecognition of objects when feeling, a disorder of perception of one’s own body. It is diagnosed according to the study of the neuropsychiatric status, the results of neuroimaging (CT. MRI of the brain). Treatment is carried out with etiotropic, vascular, neurometabolic, cholinesterase pharmaceuticals in combination with psychotherapy, speech therapy classes.
Gnosis in Greek means “knowledge”. It is the highest nervous function that provides recognition of objects, phenomena, and one’s own body. Agnosia is a complex concept that includes all violations of the gnostic function. Gnosis disorders often accompany degenerative processes of the central nervous system, are observed in many organic brain lesions resulting from injuries, strokes, infectious and tumor diseases. Classical agnosia is rarely diagnosed in young children, since their higher nervous activity is in the development stage, the differentiation of cortical centers is not complete. Gnosis disorders occur more often in children over 7 years of age and in adults. Women and men get sick equally often.
Gnostic disorders are caused by pathological changes in the secondary projection-associative fields of the cerebral cortex. The etiofactors of the lesion of these zones are:
- Acute disorders of cerebral circulation. Agnosia occurs as a result of the death of neurons of secondary fields in the area of ischemic or hemorrhagic stroke.
- Chronic cerebral ischemia. Progressive cerebral circulatory insufficiency leads to dementia, including gnostic disorders.
- Brain tumors. The defeat of secondary cortical fields is a consequence of tumor growth, leading to compression and destruction of surrounding neurons.
- Traumatic brain injury. Agnosia occurs mainly in brain injury. It develops as a result of damage to the secondary zones of the cortex at the time of injury and as a result of post-traumatic processes (formation of hematomas, inflammatory changes, microcirculatory disorders).
- Encephalitis. It may have a viral, bacterial, parasitic, postvaccinal etiology. It is accompanied by diffuse inflammatory processes in cerebral structures.
- Degenerative diseases of the central nervous system: Alzheimer’s disease, Schilder’s leukoencephalitis, Pick’s disease, Parkinson’s disease.
The cerebral cortex has three main groups of associative fields that provide a multi-level analysis of information entering the brain. Primary fields are connected to peripheral receptors, receive afferent impulses coming from them. The secondary associative zones of the cortex are responsible for the analysis and generalization of information coming from the primary fields. Further, the information is transmitted to the tertiary fields, where the highest synthesis and development of behavior tasks are carried out. The dysfunction of secondary fields leads to a violation of this chain, which is clinically manifested by the loss of the ability to recognize external stimuli, to perceive holistic images. At the same time, the function of the analyzers (auditory, visual, etc.) is not impaired.
Depending on the lesion area in clinical neurology, agnosia is classified into the following main groups:
- Visual — the absence of recognition of objects, images while maintaining visual function. It develops in the pathology of the occipital, posterior parietal cortex.
- Auditory — loss of the ability to recognize sounds and phonemes, to perceive speech. Occurs when the cortex of the superior temporal gyrus is affected.
- Sensitive – violation of the perception of one’s own body and recognition of tactile sensations. It is caused by the dysfunction of the secondary fields of the parietal divisions.
- Olfactory is an odor recognition disorder. It is observed when the mediobasal areas of the temporal lobe are affected.
- Gustatory — the inability to identify taste sensations while preserving the ability to perceive them. It is associated with pathology of the same areas as olfactory agnosia.
There is also a violation of all forms of gnosis. This pathology is designated by the term “total agnosia”.
The basic symptom of the condition is the inability to recognize perceived sensations while maintaining the ability to feel them. Simply put, the patient does not understand what he sees, hears, feels. Differentiated agnosia is often noted, due to the loss of function of a separate affected part of the cortex. Agnosia of a total nature accompanies pathological processes diffusely spreading in cerebral tissues.
Visual agnosia is manifested by the confusion of objects, the inability to name the object in question, to draw it, to draw from memory or from a drawing that has begun. When depicting an object, the patient draws only parts of it. The visual form has many variants: color, selective agnosia of persons (prosopagnosia), apperceptive – recognition of the signs of the object (shape, color, size) is preserved, associative – the patient is able to describe the object as a whole, but cannot name it, simultaneous – inability to recognize the plot of several objects while maintaining recognition of each object separately, visual-spatial – violation of the gnosis of the mutual arrangement of objects. The disorder of recognition of letters and symbols leads to dyslexia, dysgraphy, loss of the ability to do arithmetic calculations.
Auditory agnosia when the dominant hemisphere is affected leads to partial or complete misunderstanding of speech (sensory aphasia). The patient perceives phonemes as meaningless noise. The condition is accompanied by compensatory verbosity with repetitions, insertion of random sounds, syllables. Omissions and permutations may be noted when writing. The reading is saved. The defeat of the subdominant hemisphere can lead to loss of musical hearing, the ability to recognize previously familiar sounds (rain noise, dog barking), to understand the intonation features of speech.
Sensitive agnosia is characterized by a disorder of the gnosis of irritations perceived by pain, temperature, tactile, proprioceptive receptors. It includes asteriognosis — the inability to identify an object by touch, spatial agnosia – a violation of orientation in a familiar area, a hospital ward, one’s own apartment, somatognosia – a disorder of feeling one’s own body (proportionality, size, presence of its individual parts). Common forms of somatognosia are finger agnosia — the patient is unable to name the fingers, show the finger indicated by the doctor, autotopagnosia – a feeling of absence of a separate part of the body, hemisomatoagnosia – a feeling of only half of his body, anosognosia – unconsciousness of the presence of a disease or a separate symptom (paresis, hearing loss, visual impairment).
The examination is aimed at identifying agnosia, searching for its cause. Determination of the clinical form of agnosia allows to establish the localization of the pathological process in the brain. The main diagnostic methods are:
- Interviewing the patient and his relatives. The aim is to establish complaints, the onset of the disease, its connection with trauma, infection, disorders of cerebral hemodynamics.
- Neurological examination. During the study of neurological and mental status, along with agnosia, a neurologist identifies signs of intracranial hypertension, focal neurological deficit (paresis, sensitivity disorders, disorders of the cranial nerves, pathological reflexes, changes in the cognitive sphere) characteristic of the underlying disease.
- Consultation of a psychiatrist. It is necessary to exclude mental disorders. It includes a pathopsychological examination, a study of the personality structure.
- Tomographic studies. CT, MSCT, and MRI of the brain make it possible to visualize degenerative processes, tumors, inflammatory foci, stroke zones, and traumatic injury.
Agnosia is only a syndrome, a syndromic diagnosis can take place at the initial stage of diagnosis. The result of the above studies should be the establishment of a complete diagnosis of the underlying disease, the clinical picture of which includes gnosis disorder.
Therapy depends on the underlying disease, may consist of conservative, neurosurgical, rehabilitation methods.
- Vascular and thrombolytic pharmaceuticals. They are necessary for the normalization of cerebral blood flow. Acute and chronic cerebral ischemia is an indication for the appointment of drugs that dilate cerebral vessels (vinpocetine, cinnarizine), antiplatelet agents (pentoxifylline). With intracranial hemorrhage, antifibrinolytic drugs are used, with thrombosis — thrombolytics.
- Neurometabolites and antioxidants: glycine, gamma-aminobutyric acid, piracetam, pyritinol, oxymethylethylpyridine. They improve metabolic processes in cerebral tissues, increase their resistance to hypoxia.
- Anticholinesterase agents: rivastigmine, donepezil, ipidacrine. Normalize neuropsychological, cognitive functions.
- Etiotropic therapy of encephalitis. In accordance with the etiology, it is carried out with antibacterial, antiviral, antiparasitic drugs.
Rehabilitation of patients lasts at least three months, includes:
- Psychotherapy. Art therapy, cognitive behavioral therapy are aimed at restoring the mental sphere of the patient, adapting to the situation that has developed in connection with the disease.
- Classes with a speech therapist. They are necessary for patients with auditory agnosia, dyslexia, dysgraphia.
- Occupational therapy. It helps patients overcome feelings of inferiority, distract from experiences, improve social adaptation.
Neurosurgical treatment may be required in case of traumatic brain injury, cerebral tumor. It is carried out against the background of conservative therapy with subsequent rehabilitation.
Prognosis and prevention
The success of treatment depends on the severity of the underlying disease, the age of the patient, and the timeliness of the therapy. Agnosia that occurs in young patients due to trauma, encephalitis regresses during treatment for 3 months, in severe cases, the recovery process takes up to 10 months. Agnosia of tumor genesis depends on the success of the removal of the formation. With degenerative processes, the prognosis is unfavorable, treatment only allows you to stop the progression of symptoms. Prevention consists in timely treatment of vascular pathology, prevention of head injuries, oncogenic effects, infectious diseases.