What is Agnosia, Know its Causes, Symptoms, Treatments, Types, Prognosis, Pathophysiology, Prevention

Agnosia is a rare neurological disorder which causes the loss of ability to recognize any familiar person, object and sounds or the ability to comprehend the meaning of any object or difficulty in processing sensory information, such as touch, sound, and light even in the presence of intact senses. In Agnosis, brain lesions develop due to neurological ailments or brain injury mainly in the occipital, temporal, or parietal lobe of the ventral stem of the brain. Other than neurological illness, Agnosia can also result from cerebral stroke, severe head injury, developmental disorders, or dementia.

There are different types of agnosia depending on the perception of vision, auditory, or touch senses. The types of agnosia are as follows:

• Visual Agnosia: Inability to recognize any familiar objects.
• Cerebral Akinetopsia: Inability to sense any sorts of visual motion.
• Simultagnosia: Inability to access through any visual input completely.
• Topographical Agnosia: In this type of Agnosia, Patient doesn’t rely only on visual cues for directional guidance as he has difficulty in recognizing any objects. It is also known as topographical disorientation or topographagnosia.
• Apperceptive Visual Agnosia: Inability to differentiate between various visual shapes and also inability to recognize, copy, or discriminate between different visual stimuli.
• Associative Visual Agnosia: In this type of agnosia, patient can explain various visual scenes but has difficulty in recognition.
• Prosopagnosia or Facial Agnosia: Cannot recognize any familiar faces including their own consciously.
• Finger Agnosia: Inability to identify the fingers on the hand in a separate manner.
• Analgesia or Pain Agnosia: Difficulty in processing and perceiving any sorts of painful sensation.
• Autotopagnosia: Inability to identify the orientation of different body parts.
• Cerebral Achromatopsia or Color Agnosia: Difficulty in categorizing or recognizing different colors.
• Pure Alexia: Inability to recognize any kind of written or readable text.
• Astereognosis or Somatosensory Agnosia: Difficulty in recognizing objects by tactile or touch sensation.
• Tactile Agnosia: In this type of agnosia, there is loss of ability to identify or recognize objects by touch sense only.
• Auditory Agnosia: Difficulty in differentiating non-verbal auditory or environmental sounds including speech and non-speech sounds, despite hearing capability is unimpaired.
• Cortical Deafness: Hearing is intact but does not perceive any kind of auditory information.
• Auditory Verbal Agnosia or Pure Word Deafness: Hearing is intact but there is a loss of ability to recognize spoken words.
• Semantic Agnosia: In this type of Agnosia, patient is able to use only non-visual sensory systems for object recognition.
• Visuospatial Dysgnosia: Loss of the sense of “whereness” with respect to one’s environment or related objects.
• Phonagnosia: Although, the listener can understand the words but fail to recognize the familiar voice.
• Environmental Agnosia: Inability to locate or identify direction leading to familiar buildings or rooms.
• Time Agnosia: In this type of agnosia, there is loss of ability to comprehend succession and also durations.
• Anosognosia: Inability to gain feedback about any condition due to lack of insight.
• Form Agnosia: Patients can only identify parts of details, not the complete object.
• Social-emotional Agnosia or Expressive Agnosia: Unable to distinguish body language, facial expression, or any kind of intonation, and also the loss of ability to understand people’s emotions non-verbally thereby limiting social interaction.
• Integrative Agnosia: The ability to recognize elements separately but can recognize object by integrating those elements as a whole.

Symptoms of Agnosia usually vary depending on the position and parts of different sensory lobe of the brain which is damaged:

• Symptoms of Agnosia When Occipital Lobe is Damaged: This lobe deals with the normal perception of vision processing. When this lobe gets damaged or affected by any neurological illness, then visual agnosia occurs in which patient would have symptoms of loss of ability to identify geometric shapes, features, or colors of any common objects or unable to recognize known faces or any buildings, rooms, or places, but the visual perception is totally unaffected.
• Symptoms of Agnosia When Temporal Lobe is Damaged: Damage of this lobe leads to auditory agnosia as the lobe functions for sound detection. In this case, the symptoms would include people being able to hear the sound but unable to recognize the familiar voice, sounds, or the language spoken.
• Symptoms of Agnosia When Parietal Lobe is Damaged: This lobe functions to detect sensory information related to touch, pain, or temperature. When this lobe gets damaged, tactile agnosia occurs in which people fails to perceive pain sensation or face difficulty in identifying any familiar object by touching only; however, this patient can recognize the object when he sees it.

Agnosia is a very rare neurological disorder; amongst those, the prevalence rate of visual or auditory agnosia is much higher than the tactile agnosia. It affects a large number of people all over the world in a year.

Agnosia can result in negotiation with the quality of life. Recovery process basically varies as it is influenced by the age of the patient, the degree of impairment, type and size of damage, location and intensity of the brain lesions and finally, the effectiveness of the treatment procedure. With the beginning of appropriate treatment and therapies, Agnosia patient shows recovery within the first 3 months of time but to attain complete cure it can take 1 to 2 years.

Agnosia occurs when the brain suffers from any kind of trauma or damage in certain signaling pathways that deals with sensory processing, storing information and knowledge. It also integrates memory with recognition and perception. Brain lesions in the parietal, occipital, or temporal lobes of the brain due to sudden head traumas, strokes, or encephalitis, etc. result in agnosia. Other conditions that lead to agnosia include impairment or damage of the brain lobes, carbon monoxide poisoning, dementia, tumors, anoxia, abscesses or pockets of pus, developmental disorders, hereditary or acquired brain infection, sudden recovery from blindness, or progressive neurodegenerative disorders like Alzheimer disease.

The superior temporal sulcus of the human brain is very much essential for the comprehension of speech because this region is highly functional with the involvement of lexical interface. Evidences show that the presence of bilateral lesions mainly in the superior temporal sulcus leads to Pure Word Deafness or Speech Agnosia. As the lexical interface is related to phonemes or sound waves along with various morphological features in order to yield meaningful words; therefore, any sorts of damage, brain injury, or neurological illness affects the superior temporal sulcus of the brain and thereby give rise to several forms neurolinguistic deficiencies or sensory perception disorders including Agnosia.

The risk factors associated with Agnosia include the following:

• Caucasian race is more prone to Agnosia
• Agnosia most commonly affects women
• Older age
• Any types of severe head injury
• Smoking habit
• Obesity
• If an individual is suffering from the vascular illness like coronary heart disease, hypercholesterolemia, atherosclerosis, diabetes, hypertension, etc.

The probable complications related to agnosia are mentioned in the following points:

• Mild to severe hallucinations
• Spatial perception disorders.

In order to diagnose an individual for agnosia, it must be seen that the patient has intact language abilities, response to stimuli, and intelligence but is suffering from a loss of sensation. Moreover, the patient should only be experiencing sensory deficit only in one of the sensory modalities.

• A doctor’s evaluation in which a doctor will ask the patient to recognize and identify common things in the house by the perception of vision, hearing, or touch.
• Standardized tests of brain functions including neuropsychological testing are done to diagnose Agnosia more accurately.
• Imaging tests, such as magnetic resonance imaging or MRI, computed tomography or CT scan, etc. are done in presence or absence of angiographic protocols in order to identify hemorrhage, infarction, tumor mass, lesions, or to detect atrophy.
• Fundus examination, cerebrospinal fluid examination, and electroencephalogram test also show an abnormal result.
• Other differential diagnostic tests can be done depending on the similar symptoms of some diseases like memory disorders, mental retardation, etc.

Treatment of agnosia is basically supportive and symptomatic. In some cases, the cause of agnosia is treated through surgery, use of antibiotics for cerebral abscess, certain brain protein hydrolyzing drugs, such as Piracetam tablets, or radiation for a brain tumor. Different types of speech or occupational therapies or rehabilitation can help to reverse the effects of Agnosia. These therapeutic strategies include the following:

• Alternate Hints for Coping with Agnosia: This strategy can be specifically used for patients suffering from prosopagnosia or environmental agnosia and this may include touch perception or cues for scar marks on any individuals’ face or presence of crooked teeth for identifying any individual or even color cues.
• Alternative Perception for Managing Agnosia: This strategy to treat agnosia includes the use of an unaffected sensory modality, such as the use of tactile perception in place of visual senses or use of auditory information in place of visual perception when visual senses are affected.
• Verbal Description for Agnosia: Verbal explanations may sometimes be helpful for patients with different types of agnosia.
• Structural Approaches for Treating Agnosia: Structural strategies, such as organizing clothes, tactile cues to identify certain types of clothing, etc. can be extremely useful for a patient with visual agnosia.

As such there are no preventive measures for agnosia. However, it can be restricted to a certain level through early detection of the disease associated with proper medical treatments and related therapies. Also, the affected individual can follow the below-mentioned diet items in order to prevent further complications:

• More consumption of fresh fruits and vegetables, dairy products, soybean, walnut oil, oily foods, seafood, and sweets.
• Limit the consumption of fish and meat.

Agnosia cannot be prevented, but the condition can improve hugely with proper diagnosis and treatment depending on the extent of damage. Handling any agnosia patients require much care and cautious attitude. For safety reason, agnosia patient should always be accompanied with the contact details of their relatives or any sorts of electronic locator devices attached to their clothing.

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