What Is Agnosia?

HealthInfi.png343d

Overview

Agnosia is characterized by an inability to recognize and identify objects and/or persons. Symptoms may vary, according to the area of the brain that is affected. It can be limited to one sensory modality such as vision or hearing; for example, a person may have difficulty in recognizing an object as a cup or identifying a sound as a cough.

Agnosia can result from strokes, traumatic brain injury, dementia, a tumor, developmental disorders, overexposure to environmental toxins (e.g., carbon monoxide poisoning), or other neurological conditions. Visual agnosia may also occur in association with other underlying disorders. People with agnosia may retain their cognitive abilities in other areas. Treatment of primary agnosia is symptomatic and supportive; when it is caused by an underlying disorder, treatment of the disorder may reduce symptoms and help prevent further brain damage

Synonyms of Primary Visual Agnosia

  • agnosis, primary
  • apperceptive agnosia
  • associative agnosia
  • monomodal visual amnesia
  • visual amnesia

Signs & Symptoms

People with primary visual agnosia may have one or several impairments in visual recognition without impairment of intelligence, motivation, and/or attention. Vision is almost always intact and the mind is clear. Some affected individuals do not have the ability to recognize familiar objects. They can see objects, but are unable to identify them by sight. However, objects may be identified by touch, sound, and/or smell. For example, affected individuals may not be able to identify a set of keys by sight, but can identify them upon holding them in their hands.

Some researchers separate visual agnosia into two broad categories: apperceptive agnosia and associative agnosia. Apperceptive agnosia refers to individuals who cannot properly process what they see, meaning they have difficult identifying shapes or differentiating between different objects (visual stimuli). Affected individuals may not be able to recognize that pictures of the same object from different angles are of the same object. Affected individuals may be unable to copy (e.g., draw a picture) of an object.

Associative agnosia refers to people who cannot match an object with their memory. They can accurately describe an object and even draw a picture of the object, but are unable to state what the object is or is used for. However, if told verbally what the object is, an affected individual will be able to describe what it is used for.

In some cases, individuals with primary visual agnosia cannot identify familiar people (prosopagnosia). They can see the person clearly and can describe the person (e.g., hair and eye color), but cannot identify the person by name. People with prosopagnosia may identify people by touch, smell, speech, or the way that they walk (gait). In some rare cases, affected individuals cannot recognize their own face.

Some people have a form of primary visual agnosia associated with the loss of the ability to identify their surroundings (loss of environmental familiarity agnosia). Symptoms include the inability to recognize familiar places or buildings. Affected individuals may be able to describe a familiar environment from memory and point to it on a map.

Primary agnosia is associated with bilateral damage to the ventral visual stream, including the lingual and fusiform gyri.

Primary visual agnosia can be distinguished from other visual disorders such as simultanagnosia that is a characterized by the inability to read and the inability to view one’s surroundings as a whole. The affected individual can see parts of the surrounding scene, but not the whole. There is an inability to comprehend more than one part of a visual scene at a time or to coordinate the parts.

In rare cases, people with primary visual agnosia may not be able to recognize or point to various parts of the body (autotopagnosia). Symptoms may also include loss of the ability to distinguish left from right.

Causes

Primary visual agnosia is a rare neurological disorder that occurs as a result of damage to the brain. Symptoms develop due to the inability to retrieve information from those damaged areas that are associated with visual memory. Lesions may occur as a result of traumatic brain injury, stroke, tumor, or overexposure to dangerous environmental toxins (e.g., carbon monoxide poisoning). In some cases, the cause of the brain damage may not be known. Symptoms may vary, according to the area of the brain that is affected.

Visual agnosia may also occur in association with other underlying disorders (secondary visual agnosia) such as Alzheimer’s disease, agenesis of the corpus callosum, MELAS, and other diseases that result in progressive dementia. (For more information on these disorders, choose “Alzheimer,” “Agenesis of the Corpus Callosum,” and “MELAS” as your search terms in the Rare Disease Database.)

Organizations

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Where to Start

The Merck Manuals Online Medical Library provides information on this condition for patients and caregivers.

The National Institute of Neurological Disorders and Stroke (NINDS) collects and disseminates research information related to neurological disorders. Click on the link to view information on this topic.

The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.

PubMed is a searchable database of medical literature and lists journal articles that discuss Agnosia. Click on the link to view a sample search on this topic.

Affected Populations

Primary visual agnosia is an extremely rare neurological disorder that affects males and females in equal numbers. The first detailed account of visual agnosia in the medical literature occurred in 1890.

Related Disorders

The following disorders may precede the development of primary visual agnosia. They can be useful in identifying an underlying cause of some forms of this disorder.

Alzheimer’s disease is a common, progressive, degenerative brain disorder affecting memory, thought, and language. Neurodegenerative changes lead to the formation of plaques or patches within the brain and the loss of cholinergic neurotransmitter function.

The early behavioral changes may be subtle; however, as the disease progresses, memory losses increase and there are personality, mood, and behavioral changes. There may also be disturbances of judgment, concentration, and speech along with confusion and restlessness. (For more information on this disorder, choose “Alzheimer” as your search term in the Rare Disease Database.)

Pick’s disease is a degenerative neurological disorder that affects the frontal and temporal lobes of the brain. The symptoms of Pick’s disease closely resemble those of Alzheimer’s disease. In the early stages, memory is still intact and there is a high degree of disorientation. In the later stages of this disorder, there is a loss of motor control and language skills.

Pick’s disease usually begins between the ages of forty and sixty and appears to affect females more often than males, and the exact cause is not known. The area of the brain affected is the major different in Pick’s disease from other forms of senile dementia. This disease involves atrophy limited to the lobes of the brain.

Areas of degeneration are identified by the presence of Pick cells and Pick inclusion bodies instead of plaques and tangles. There may also be severe dementia. (For more information on this disorder, choose “Pick” as your search term in the Rare Disease Database.)

Balint’s syndrome is a rare neurological disorder associated with bilateral changes in posterior parietal cortex. It is characterized by the inability to voluntarily look at objects to the side (peripherally). An affected individual may also have trouble grasping objects due to difficulties with hand-to-eye coordination and may be unable to follow objects across the eyes’ field of vision.

Individuals often cannot read and the inability to view one’s surroundings as a whole (simultanagnosia). Although the exact cause of Balint’s syndrome is not known, it is thought that symptoms may be caused by improper development of part of the brain.

What are the possible Complications of Primary Visual Agnosia?

Complications may arise due to primary visual agnosia. Brain damage may worsen in individuals with the disorder and could spread to other parts of the brain.

Cataracts may also arise due to Primary Visual Agnosia. This results in hazy vision due to clouding in the lens of the eye.

In some cases, glaucoma may also occur. In these individuals, permanent vision damage and blindness can occur if left untreated.

In rare cases, autotopagnosia can also result. In these cases, individuals may not be able to recognize or point to body parts when asked to identify them.

Diagnosis

A variety of psychophysical tests can be conducted to pinpoint the nature of the visual process that is disrupted in an individual. Brain damage that causes visual agnosia may be identified through imaging techniques, including computed tomography (CT scan) and magnetic resonance imaging (MRI).

For more information visit us our website: https://www.healthinfi.com

1 250

No Comments

    Leave a Reply