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Agnosia
Introduction
Agnosia is a rare disorder whereby patients cannot recognize and identify objects, persons, or sounds using 1 or more of their senses despite otherwise normally functioning senses. Memory, attention, language problems, or unfamiliarity with the stimuli cannot explain the deficit. Usually, 1 of the sensory modalities is affected. For example, a patient with agnosia may not be able to identify a cup by sight, although they may be able to tell its color and identify it by touch by its shape and texture. It is not the same as anomia. Anomia is a naming disorder in which patients cannot name an object despite using their other sensory modalities like touch and smell.[1]
Classically, there are 2 forms of agnosia: apperceptive and associative.
- Apperceptive agnosia is a failure in recognition due to deficits in the early stages of perceptual processing.
- Associative agnosia is a failure in recognition despite no deficit in perception. Associative agnosia patients can typically draw, match, or copy objects, while apperceptive agnosia patients cannot.[1][2]
Types of Agnosia
There are 3 main types of agnosia, based on the type of sensation involved.
- Visual (vision)
- Auditory (hearing)
- Tactile (touch)
Visual Agnosia
Visual agnosia is an impairment in recognizing visually presented objects despite otherwise normal visual field, acuity, color vision, brightness discrimination, language, and memory. Patients can recognize objects using other sensory modalities. Sometimes, impairment is worse for certain objects, so various objects should be tested to diagnose precisely. Visual agnosia is the most common and better-understood agnosia.
Agnosia is further divided into 2 subtypes: apperceptive visual agnosia and associative visual agnosia.
- Apperceptive visual agnosia refers to an abnormality in visual perception and discriminative process despite the absence of elementary visual deficits. These people cannot recognize objects, draw, or copy a figure. They cannot perceive the correct forms of the object, although knowledge of the object is intact. Apperceptive visual agnosia is typically associated with lesions to the parietal, occipital cortex.
- Associative visual agnosia refers to difficulty understanding the meaning of what they see. They can draw or copy but do not know what they have drawn. They correctly perceive the form and know the object when tested with verbal or tactile information but cannot identify it. They cannot link 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 is the inability to recognize familiar faces. Patients can often identify other aspects like gender, hair, and emotions. Prosopagnosia results from damage to the fusiform face area (located in the inferior temporal cortex in the fusiform gyrus). People with apperceptive prosopagnosia cannot perceive facial expressions and cues but recognize non-facial clues like hair and clothing. Associative prosopagnosia patients can derive some facial information like gender and age. Mr. P in Oliver Sack’s book The Man Who Mistook His Wife for a Hat presents a classic case of prosopagnosia.
- Simultanagnosia is the inability to recognize and sort out objects when they appear together, but they can recognize them when they appear alone. Patients cannot perceive the overall meaning of a picture or multiple things together, although they can describe isolated elements. Two forms of simultagnosia have been described.
- Dorsal simultagnosia: Patients cannot see more than 1 object at a time. For example, when presented with a picture of a table, chair, and flower vase, they may report only 1 thing at a time. When their attention is diverted to the other thing, they can identify only that thing; other things disappear. They often have difficulty reading as it involves viewing more than 1 word at a time. They often bump into objects that are close together. Dorsal simultagnosia is typically associated with lesions in the bilateral occipitotemporal cortex.
- Ventral simultagnosia: These individuals cannot identify more than one object or complex object at a time, although they can see more than one object at a time. They cannot perceive the whole picture as 1 and derive meaning from it. For example, in a night sky picture with stars and a full moon, they may identify the moon as a ball, unable to derive the meaning of the whole picture. Ventral simultagnosia is associated with lesions in the left inferior occipital area.
- Color agnosia is the inability to identify and distinguish colors despite intact basic color vision and brightness discrimination mechanisms. Diagnosing this type of agnosia is very difficult as colors can only be appreciated visually. Usually, these patients have a lesion in the left occipitotemporal region of the brain.
- Topographical agnosia is the inability to orient to surroundings because of the inability to interpret spatial information. These patients have a good memory of the layout and specifics of the places well known to them, but they cannot navigate their way through. They cannot use visual cues to guide them in the right direction. It is associated with a lesion in the right posterior cingulate area of the brain.
- Finger agnosia is a difficulty naming and differentiating among the fingers of either hand and the hands of others. It does not refer to the inability to identify a finger as a finger, as the name may suggest. It is a part of the constellation of symptoms often referred to as Gerstmann syndrome, which includes acalculia, agraphia, finger agnosia, and left-right disorientation.
- Akinetopsia refers to the inability to perceive motion.
- Agnostic alexia refers to the inability to recognize words visually. They can still write and talk without difficulty.
Auditory Agnosia
- Auditory agnosia is the inability to recognize sounds despite intact hearing. It is typically associated with right-side temporal lesions.
Types of Auditory Agnosia
- Phonagnosia is the inability to recognize familiar voices. They can recognize words spoken by others. It is caused by damage to certain parts of the sound association region.
- Verbal auditory agnosia or pure word deafness is the inability to comprehend spoken words but to read, write, and speak relatively normally.
- Nonverbal auditory agnosia is the inability to comprehend nonverbal sounds and noises, with sparing of speech comprehension.
- Amusia is the inability to recognize music. People with amusia are unable to comprehend that certain types of sounds represent music and, therefore, cannot distinguish music from other sounds.
Tactile Agnosia
Tactile agnosia refers to the inability to recognize objects by touch. They can name objects by sight.
- Amorphognosia is the inability to identify the size and shape of objects by touch, for example, a triangle or square.
- Ahylognosia is the inability to identify distinctive qualities like texture and weight, such as in a piece of wood, cotton, or metal.
- Tactile symbols are impaired recognition by touch in the absence of amorphognosia and anosognosia.[3][4][5][6][7]
Etiology
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Etiology
Agnosia can result from various neurological conditions like strokes, tumors, infections, dementia, hypoxia, toxins such as carbon monoxide poisoning, head injury, developmental disorders, or other neurological conditions. It can present suddenly, for example, in stroke or head injury, or gradually, for example, in tumors and dementia. Symptoms depend on the area involved. People with agnosia usually retain their other cognitive abilities. Agnosia happens when there is brain damage along pathways that connect primary sensory processing areas. These areas typically include the posterior parietal cortex and occipitotemporal regions.
Epidemiology
Pure forms of agnosia are very rare. Less than 1% of all neurological patients have agnosia. Visual agnosia is the most common and better-described type of agnosia.[1][2]
History and Physical
Careful patient history is very important in cases of suspected agnosia. Clues to diagnosis and etiology often involve a detailed interview with the patient, family members, and caregivers. It is harder to diagnose when the patient lacks insight into their deficits. History reveals clues pointing to the type of agnosia. For example, a patient with visual agnosia specify problems in day-to-day life, for example, getting dressed or the inability to differentiate a fork and a knife because of an inability to recognize certain types of objects visually. Patients with topographical agnosia present with often lost findings directions. Patients with akinetopsia often bump into things, get confused about how things got moved around, have difficulty crossing roads and driving, and are accident-prone. Patients with simultagnosia often have trouble reading, writing, and interpreting multiple things at a time.
Other important points to elicit in history can confirm that other sensory modalities, memory, and cognition are not affected. Initial assessment involves asking patients to identify common objects through sight, touch, and smell. A thorough physical examination is done to detect any primary deficits in individual senses (visual fields, acuity, reading, drawing, hearing tests, among others) or the ability to communicate that may interfere with identifying the objects (memory, cognition, attention, aphasia). An important aspect of diagnosing agnosia is ruling out alternative explanations. Recognition disturbance can occur in many other neurological conditions. Still, agnosia can be diagnosed only in the absence of aphasia, generalized dementia, delirium, or any deficit that may impair some or all of the information-processing steps involved in object recognition. It is very important to rule out genuine unfamiliarity with stimuli. It is important to consider cultural and life experiences and other factors that may lead to unfamiliarity. Testing of common objects and constructing a balanced set of items that are determined individually should be done.
For example, to assess for visual agnosia, show the patient several familiar items like keys, a pen, and a banana and ask to name them. Differentiating visual agnosia and aphasia is important. For prosopagnosia, show the patient pictures of famous people, their family members, and themselves. For color agnosia, show solid color cards and ask them to name the colors. For simultagnosia, present pictures with several objects or people and ask them to identify what they see. For tactile agnosia, make sure the patient cannot see, then put common things in each hand 1 by 1 and ask the patient to identify them by touch alone. The inability to correctly identify at least 50% of stimuli tested suggests the diagnosis of agnosia.[1][2][3][8]
Evaluation
Diagnosis is mainly clinical, based on the clinical history and physical examination, which includes a thorough neurologic exam, psychological exam, and certain standardized tests of brain function. It is important to ensure that the abnormality cannot be explained in another way, for example, genuine unfamiliarity with the stimuli, poor instructions, overlooked diseases like neuropathy and cataracts, or other neurologic conditions like dyspraxia or dysphasia. Various standardized tests are available to test for memory and cognition (MMSE, Montreal Cognitive Assessment, ADAS-cog) and aphasia (Boston Naming Test, Western Aphasia Battery). Diagnosis is supplemented by neuroimaging tests such as head CT and brain MRI to look for etiology. More testing may be needed based on clinical judgment and suspected etiology. Auditory or visual evoked potentials may be used to determine whether a deficit exists in the sensory projection area instead of the primary sensory or association cortex.
Treatment / Management
Agnosia can considerably limit the everyday functioning of the patients. It can also significantly affect the lives of family and caretakers. There is no direct cure. Treat the underlying cause when possible. For example, treating and preventing stroke, antibiotics and/or surgery for a brain abscess, and surgery or radiation for brain tumors. Agnosia is managed supportively. Rehabilitation, speech, and occupational therapy play an important role in treating agnosia and mainly focus on teaching patients to use intact sensory modalities to compensate. Restorative training has limited utility. Interventions focus on helping these patients and their families and caregivers cope and adapt to the condition and help patients function independently within their context. Counseling family members and helping them with behavioral changes are equally important. Rehabilitation approaches must be individualized and focus on the specific deficit by developing compensatory strategies.
Alternative Cues and Strategies
Some general strategies can be used are alternative cues, such as teaching people with prosopagnosia to identify facial scars or hairstyles. For patients with visual agnosia, teaching alternative strategies like learning to identify everything by touch; for patients with prosopagnosia, teaching voice recognition for people; and teaching patients with auditory agnosia to lip read and write everything.
Organizational Strategies
- Provide a predictable environment and consistency in performing a task, for example, placing things in the same place daily. Routines help develop consistency in performing a task.
- Declutter. For example, patients should keep things they use every day in one place. This may help patients with visual agnosia.
- Label everything.[8][9][10] (B3)
Differential Diagnosis
It is important to remember that pure forms of agnosia are very rare. It is important to evaluate and rule out dementia, aphasia, acute confusional states (delirium), attention disturbance, and unfamiliarity with stimuli. Also, clinicians need to confirm no sensory impairment, such as color blindness, cataracts, hearing loss, or neuropathy.
Prognosis
Few patients with agnosia regain their sensory function. Most recovery occurs within the first 3 months and, to a variable degree, may continue up to a year. The prognosis depends on the patient's age, etiology, type, size, and location of the area affected, the extent of impairment, and the effectiveness of therapy.
Enhancing Healthcare Team Outcomes
The diagnosis and management of agnosia are complex. Once the diagnosis is made, an interprofessional team may be needed for a detailed evaluation of sensory and neurobehavioral status, including ophthalmology, speech pathology, neurology, audiology, speech, psychiatry, occupational therapy, and specialty care nurses. After the tentative diagnosis of agnosia is made, a thorough neuropsychological examination is done to test intelligence, memory function, linguistic competence, and assess sensory-perceptual processing. Occupational therapists assist with treatment and should provide feedback to the team. Specialty care neuroscience nurses should work with the team to coordinate care, be involved in patient education, and monitor compliance. The interprofessional team can thus improve outcomes for patients with agnosia. For most patients with agnosia, full recovery is not possible, and the quality of life is diminished. Depending on which organ system is affected, some therapy can be recommended. Even when recovery occurs, it is rarely complete. Mostly, the prognosis is poor, and these individuals need lifelong care and close supervision.[1][8]
References
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Heutink J, Indorf DL, Cordes C. The neuropsychological rehabilitation of visual agnosia and Balint's syndrome. Neuropsychological rehabilitation. 2019 Dec:29(10):1489-1508. doi: 10.1080/09602011.2017.1422272. Epub 2018 Jan 24 [PubMed PMID: 29366371]
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