Agnosia: what is it, types, symptoms, causes, prognosis

What is Agnosia?

Agnosia Is a rare disease in which a person cannot recognize and identify objects, people or sounds, using one or more of your senses while the senses are otherwise functioning fine. The deficit cannot be explained by memory, attention, language problems, or ignorance of stimuli. Usually one of the sensory modalities is affected. For example, a patient with agnosia may not be able to visually recognize the cup, although they may be able to detect color and feel by shape and texture. This is not the same as anomie. Anomia is a naming disorder in which patients are unable to name an object despite using other sensory techniques such as touch and smell.

Two forms of agnosia are classically distinguished: apperceptive and associative.

• Apperceptive agnosia is a recognition failure due to a deficiency in the early stages of perceptual processing.
• Associative agnosia is a failure in recognition despite the absence of a perception deficit. Patients with associative agnosia can usually draw, match, or copy objects, while patients with apperceptive agnosia cannot.

Types of agnosia and their symptoms

There are 3 main types of agnosia depending on the type of sensation.

1. Visual (vision);
2. Hearing (hearing);
3. Tactile (touch).

—​ Visual agnosia.

Visual agnosia refers to impaired recognition of visually presented objects despite normal visual field, acuity, color vision, brightness discrimination, language, and memory. Patients can recognize objects using other sensory modalities. Sometimes the recognition deteriorates for certain types of objects, therefore, for an accurate diagnosis, it is necessary to test various objects. Visual agnosia — the most common and well-studied agnosia.

Further, agnosia is divided into 2 subtypes: apperceptive visual agnosia and associative visual agnosia.

• Apperceptive visual agnosia refers to anomalies of visual perception and discriminatory process, despite the absence of elementary visual impairments. These people cannot recognize objects, draw or copy shapes. They cannot perceive the correct forms of the object, although the knowledge of the object remains unchanged. Apperceptive visual agnosia is usually associated with damage to the parietal, occipital cortex.
• Associative visual agnosia means having difficulty understanding the meaning of what the patients see. They can draw or copy, but they don't know what they are drawing. Patients correctly perceive the form and know the object when checking verbal or tactile information, but cannot identify the object. They cannot relate the fully perceived visual stimulus to prior experience to help them recognize the stimulus. Associative visual agnosia is usually associated with damage to the bilateral inferior occipitotemporal cortex.

Types of visual agnosia:

• Prosopagnosia — inability to recognize familiar faces. Patients can often identify other aspects such as gender, hair, emotions. Prosopagnosia results from damage to the fusiform region of the face (located in the inferior temporal cortex in the fusiform gyrus). People with apperceptive prosopagnosia cannot perceive facial expressions and signals, but they can recognize non-facial features such as hair and clothing. Patients with associative prosopagnosia can obtain some information about the face, such as gender and age.
• Simultanagnosia — inability to recognize and sort objects when they appear together, but sufferers can recognize them when they appear alone. Patients cannot perceive the general meaning of an image or several things together, although they can describe individual elements. Two forms of simultagnosia are described.
  1. Dorsal simultagnosia: patients cannot see more than one object at a time. For example, when they are shown a picture of a table, a chair, and a flower vase, they can only communicate one thing at a time. When their attention turns to another thing, they can only identify that thing; other things disappear for them. Patients with this form of simultagnosia often have difficulty reading because they need to look at more than one word at a time. They often bump into objects that are close to each other. Dorsal simultagnosia is usually associated with involvement of the bilateral occipitotemporal cortex.
  2. Ventral simultagnosia: these people also cannot identify more than one object or complex objects at the same time, although they can see more than one object at the same time. Patients cannot perceive the whole picture as a whole and derive meaning from it. For example, in an image of a night sky with stars and a full moon, they may identify the moon as a ball without being able to understand the meaning of the entire image. Ventral simultagnosia is associated with damage to the left lower occipital region.
• Color agnosia — inability to identify and distinguish colors, despite the preservation of the basic mechanisms of color vision and brightness discrimination. This type of agnosia is very difficult to diagnose as colors can only be assessed visually. Typically, these patients have a lesion in the left occipitotemporal region of the brain.
• Topographic agnosia — inability to navigate the environment due to inability to interpret spatial information. These patients remember well the location and features of places they know well, but cannot navigate them. Patients cannot use visual cues to direct themselves in the right direction. Associated with a lesion in the right posterior cingulate part of the brain.
• Finger agnosia — difficulty in identifying and distinguishing between the fingers of one hand and the hands of others. This does not refer to the inability to identify a finger as a finger, as the name suggests. It is part of a group of symptoms often called Gerstmann's syndrome, which includes acalculia, agraphia, agnosia of the fingers, and left-right disorientation.
• Akinetopsia means the inability to perceive movement.
• Agnostic alexia refers to the inability to recognize words visually. People can still write and speak without difficulty.

Auditory agnosia

• Auditory agnosia — inability to recognize sounds despite intact hearing. Auditory agnosias are usually associated with right-sided temporal lobe lesions.

Types of auditory agnosia

• Phonagnosia — inability to recognize familiar voices. People can recognize words spoken by others. Phonagnosia is caused by damage to certain parts of the sound association area.
• Verbal auditory agnosia — the patient is unable to understand the spoken words, but can read, write and speak in a relatively normal way.
• Non-verbal auditory agnosia — inability to perceive non-verbal sounds and noises while maintaining understanding of speech.
• Amusia — inability to recognize music. They cannot understand that certain types of sounds represent music and therefore cannot distinguish music from other sounds.

Tactile agnosia

Tactile agnosia means the inability to recognize objects by touch. People can name objects by sight.

• Amorphognosis — an inability to feel the size and shape of objects, such as a triangle or square.
• Anosognosia — failure to identify distinctive qualities such as texture and weight, such as a piece of wood, cotton, or metal.
• Tactile Asymbolism — violation of recognition by touch in the absence of amorphognosis and achilognosia.

Causes and risk factors

Agnosia can result from various neurological conditions such as stroke, tumors, infections, dementia, hypoxia, poisoning, for example, carbon monoxide poisoning, head trauma, developmental disorders, or other neurological conditions. The condition can appear suddenly, such as with a stroke or head injury, or gradually, such as with swelling and dementia. Symptoms depend on the area affected (see (see section above). People with agnosia usually retain other cognitive abilities.

Agnosia occurs when the brain is damaged along pathways connecting areas of primary processing of sensory information. These areas usually include the posterior parietal cortex and the occipitotemporal regions.

Epidemiology

Pure agnosia is very rare. Less than 1% of all patients with neurological disorders suffer from agnosia. Visual agnosia — the most common and best described type of agnosia.

Diagnostics

Diagnosis is mainly clinical, based on medical history and physical examination, including careful neurological examination, psychological examination, and certain standardized function tests brain.

Various standardized tests are available to test memory and recognition (Concise Mental Status Scale, Montreal Cognitive Assessment Scale, Scale of Assessment Alzheimer's disease).

Diagnosis is complemented by neuroimaging tests such as CT and MRI of the brain to elucidate the etiology. Additional testing may be required based on clinical judgment and suspected etiology. Auditory or visual evoked potentials can be used to determine if there is a deficit in the sensory projection area as opposed to the primary sensory or associative cortex..

It is important to remember that pure forms of agnosia are very rare. It is important to evaluate and rule out dementia, aphasia, acute states of confusion (delirium), impaired attention and ignorance of stimuli. In addition, you need to make sure that there are no real sensory impairments such as color blindness, cataract, hearing loss, neuropathy and other disorders.

Standard therapies

Agnosia can significantly limit the daily functioning of patients. The disorder can also significantly affect the lives of the family and caregivers. There is no direct cure. If possible, treat the underlying cause. For example, they treat and prevent stroke, prescribe antibiotics and / or surgery for brain abscess, as well as surgery and / or radiation for brain tumors.

Agnosia is treated supportively. Rehabilitation, speech therapy, and occupational therapy play an important role in the treatment of agnosia and mainly focus on educating patients to use unchanged sensory modalities for compensation. Restorative training is of limited utility. Interventions are usually aimed at helping patients, their families and caregivers coping with and adapting to this disease, and helping patients to function independently in their context. It is equally important to consult with family members and help them change their behavior.

Rehabilitation approaches should be individualized and focused on the specific impairment through the development of compensatory strategies.

—Alternative tips and strategies.

Some common strategies that can be used are alternative clues, such as teaching people with prosopagnosia how to recognize any facial scars or hairstyles. For patients with visual agnosia - learning to recognize everything by touch; patients with prosopagnosia teaching voice recognition of people; to teach patients with auditory agnosia to read and write lips.

Forecast

Some patients with agnosia regain their sensory function. In most cases, recovery occurs within the first three months and, to varying degrees, can last up to a year. The prognosis depends on the patient's age, etiology (cause), type, size and location of the affected area, the degree of damage, and the effectiveness of therapy.

For most patients with agnosia, complete recovery is not possible and the quality of life deteriorates. Depending on which organ system is affected, some form of therapy may be recommended. Even when there is a recovery, it is almost never complete. For the most part, the prognosis is poor and people need lifelong care and close monitoring.