What is Astereognosis?
Astereognosis is a condition where a person can’t identify objects by touch alone, without using their sense of sight. By contrast, stereognosis (derived from the Greek words for “solid” and “knowledge”) is the ability to understand the shape, texture, size, and weight of an object by manipulating it with the hands. This skill requires functioning nerve pathways to transmit touch and position information, and a part of the brain, the parietal cortex, to interpret this information.
Astereognosis is also called somatosensory agnosia, which means the person has difficulty recognizing objects by touch, even though they don’t have a major problem with their touch sense. Impairment in object recognition by touch typically occurs due to damage to the postcentral parietal area of the brain. This inability to identify objects by touch is also associated with cognitive decline in dementia.
Astereognosis can be broken down into primary and secondary recognition deficits. The primary deficit, known as morphognosia, involves difficulty recognizing the physical attributes of an object. The secondary deficit means a person can feel an object, sense its dimensions and texture, but can’t link this with their stored information about the object to identify it.
What Causes Astereognosis?
Astereognosis, a condition where a person can’t recognize objects by touch, generally points to an issue in the part of the brain that’s opposite from the hand with this problem. Minor issues in this area could cause astereognosis, while bigger issues might cause a sensation loss in the corresponding body side.
You could also get astereognosis in both hands if there is a problem specifically in the left side of the brain, as it often takes the lead in handling touch recognition tasks. This is common in conditions like stroke or tumors. Cognitive diseases like Alzheimer’s disease can result in this too. Brain injury, especially in the parietal area, such as a compressed fracture, could also be a cause.
Other possible causes include a lack of blood supply to the corresponding brain part or mismatched blood vessels in the same area. In rare cases, issues in specific brain regions and main bundles of nerve fibers in the brain can lead to astereognosis. Tumors in the brainstem, situated at the base of the brain, can cause it in one hand. Lesions arising from lack of blood supply involving a major pathway in the brainstem are also responsible. The condition has been observed in exceptional cases of tumors outside the spinal cord near the large opening at the base of the skull and severe high spinal cord lesions caused by multiple sclerosis.
The severity of astereognosis is related to the severity of a stroke. Loss of the sense of touch is closely associated with issues in muscle movements. It’s also commonly seen in children with cerebral palsy.
Risk Factors and Frequency for Astereognosis
When looking at the impact of brain conditions like strokes, tumors, or injuries on senses, it is clear that strokes often lead to severe senses impairment. Strokes are becoming more common, with about 258 in 100,000 people suffering a stroke each year. Despite efforts to prevent them in wealthier countries, they are becoming more prevalent in areas with lower incomes. People who survive a stroke often have lasting issues.
Over the last 40 years, the number of brain tumors has also increased. This is likely due to the fact that we now have better tools to detect them. Some known causes of brain tumors include exposure to radiation, genetic mutations, hereditary conditions, and a weakened immune system. Approximately 14% of a specific type of brain tumor, known as gliomas, are found in part of the brain called the parietal lobes.
Traumatic head injuries can also lead to sensory issues and often result in a specific condition known as astereognosis. They commonly cause damage to the parietal lobe, which is a typical spot for brain fractures.
- Strokes often severely impair the senses and are becoming more common.
- The number of brain tumors has increased, likely due to improved detection tools.
- Stroke survivors often have many lasting issues.
- Known brain tumor risks include radiation, genetic mutations, hereditary conditions, and a weakened immune system.
- About 14% of gliomas occur in the parietal lobes.
- Traumatic head injuries can result in sensory problems and often damage the parietal lobe.
Signs and Symptoms of Astereognosis
Checking for peripheral sensations, like touch, pain, temperature, and vibration, is an important procedure in a neurological examination. If these tests result normal, the cortical sensory function, which is associated with the brain, can be evaluated. One of the methods is the tactile object recognition (TOR) test, also known as stereognosis. In this test, various common objects such as a pen, key, comb, and paperclip are placed in the patient’s hand when their eyes are closed. If the patient can correctly identify the object, it means their stereognosis function is working properly. Another test is the Nottingham sensory assessment, where light touch, pressure, and temperature sensitivity are measured using different tools, such as cotton wool, an index finger, neurotic pinprick and test tubes with hot and cold water.
- Tactile Object Recognition (TOR) test: A patient identifies common objects, like a pen or key, by touch.
- Nottingham sensory assessment: A range of tests check for sensitivity to touch, pressure, and temperature.
In the stereognosis evaluation, another method consists of letting the patient hold different objects like a coin or a pencil for 30 seconds and ask them to identify it. A score of 2 is given for correct identification, 1 for partially correct, and 0 for incorrect identification. It’s a trusted method for assessing stereognosis in stroke patients.
On the other hand, cortical sensory syndrome can lead to multiple problems like losing track of body position, inability to pinpoint source of pain, problems in distinguishing objects by touch, difficulties in recognizing or drawing numbers and letters, and losing ability to tell two points apart by touch. Other additional features to note are difficulties in speech, motor coordination, left-right confusion, number understanding with dominant parietal lobe involvement. Conditions like anosognosia (denying illness) and dressing apraxia (difficulty in dressing independently) are possible with nondominant parietal lobe disease.
Testing for Astereognosis
Computerized tomography (CT) and magnetic resonance imaging (MRI) are tools used to study brain disorders. CT scans are often the first choice in emergency situations because they are fast, safe to use, and can find bleeding in the brain. MRI use is growing in cases of stroke because it’s very good at detecting them.
When it comes to brain tumors, a CT scan may be the first test done to find them. It can reveal things like calcification, which is hardening of areas due to calcium, bleeding, mass effect, which refers to the effect of a growing tumor on surrounding structures, herniation, which is abnormal protrusion of brain tissue, and hydrocephalus, which is an accumulation of fluid in the brain.
However, MRI can provide more detail about the tumors. T1-weighted images enhanced with a contrast agent can show the blood vessels in the tumor and areas of dead tissue. The metabolic profile of the tumor can be assessed with an MR spectroscopy. Besides, functional MRI (fMRI), which measures brain activity by detecting changes in blood oxygen levels, is mainly used to find the link between the tumor and the brain’s eloquent areas, which are vital areas responsible for speech, movement, and other functions.
A study has shown a strong correlation between the sensory network’s connectivity and stereognosis, the ability to recognize objects by touch, after a stroke using resting-state fMRI. This means that better connectivity between networks is related to better sensory function. This imaging technique has also been used to study sensory areas in the brains of patients with congenital hemiplegia, a condition that causes paralysis on one side of the body. Diffusion tensor imaging (DTI) can assess the connectivity of the sensory tract of the path in the brain referred to as the dorsal column medial lemniscus pathway in children with hemiparesis, a condition characterized by weakness on one side of the body.
Somatosensory evoked potentials (SEP), which is a technique that assesses the brain’s electrical activity in response to sensory stimulation, can be used to relate sensory impairments such as inability to recognize objects by touch and loss of sensation on one side of the body with damage to the parietal lobes, which are regions of the brain that process sensory information, seen in imaging. SEP can also be used as a diagnostic test.
Treatment Options for Astereognosis
The treatment for astereognosis, which is the loss of the ability to recognize objects by touch, is often aimed at addressing underlying causes. For example, if the condition is caused by an acute ischemic stroke (when blood flow to an area of the brain is cut off), treatment can include medications such as thrombolytic drugs, which dissolve blood clots, mechanical thrombectomy, which is a procedure to remove the blood clot, blood pressure control measures, antiplatelet drugs, and statins.
If astereognosis is due to a brain tumor, the treatment can vary. It may include a combination of surgery, radiation therapy, or chemotherapy, depending on the tumor’s type, location, and the patient’s age.
Cognitive Rehabilitation Therapy (CRT) is another treatment used to improve cognitive problems caused by brain trauma, stroke, brain tumor, and dementia. Furthermore, sensory training, which involves hands-on exploration and discrimination of different textures, shapes, weights, and objects, can help to improve sensory discrimination after a stroke.
A study called the Study of the Effectiveness of Neurorehabilitation on Sensation (SENSe) showed that sensory discrimination training could improve functional recovery in people with impaired touch-based object recognition capabilities after a stroke.
What else can Astereognosis be?
When it comes to issues related to the sensation in one side of the body due to an issue in the parietal lobe of your brain (that’s the part of your brain that processes sensory information), doctors usually consider three main possibilities:
- Cortical Sensory Syndrome: This condition usually results in difficulty identifying the shape and size of an object by solely touching it, along with difficulty recognizing numbers or letters drawn on your skin. This is usually due to a problem in the upper back part of the parietal lobe.
- Pseudothalamic Sensory Syndrome: This condition might cause problems in feeling touch, pain, temperature, and vibration on your face, arm, and leg. This typically happens because of a problem in the front lower part of the parietal lobe.
- Atypical Sensory Syndrome: This condition results in loss of senses that can cover any sensory type, but only in particular parts of the body. This can be due to different issues in various locations of the parietal lobe.
The term ‘Astereognosis’ refers to issues with identifying an object’s shape and size merely by touching it, as well as recognizing objects by touch alone. When the basic sensory area of the parietal lobe or its connectors are damaged, these issues arise. The term ‘tactile agnosia’ is used when the issue is connected to the touch-related parts of the parietal lobe.
Some tumors in the junction where your head and neck meet can also cause similar issues by affecting the pathway that carries sensory information in your brain. Changes in the strength of the hand muscles can also be noticed, along with difficulties in recognizing shapes by touch due to lesions in the spinal cord and areas of the brainstem that manage certain senses.
What to expect with Astereognosis
Astereognosis, a common touch-related impairment after a stroke, usually gets better over time. Stroke patients typically experience improvement over days to months. This rate of recovery depends on the severity of the stroke and where it occurred in the brain.
Large parietal gliomas, a type of brain tumor, are linked with neurological issues. After tumor removal, the patient’s condition may either improve or worsen.
Even in the long-term phase, individuals with traumatic brain injuries tend to get better functionally with rehab therapy. This may include sensory re-education, which helps them regain their sense of touch.
Possible Complications When Diagnosed with Astereognosis
Loss of touch or physical sensation can negatively affect recovering patients’ abilities to perform tasks. About half of patients recovering from a stroke experience this loss of touch in their upper limb, which can interfere with its use in daily activities. The loss of discriminative touch – the ability to understand what you’re touching – is especially common in stroke patients. This can cause unexplained clumsiness.
Astereognosis – a condition where a person cannot identify an object by touching it – is linked with a decline in brain functions in Alzheimer’s disease. This condition can also result in ‘useless hand syndrome,’ where hands feel numb and clumsy. This often occurs in people with multiple sclerosis or neck disorders known as cervical spondylosis.
The same tactile impairment can happen in people with parietal lobe disease, a condition affecting the brain. This can lead to ‘tactile apraxia,’ which is a condition where hand movements for interacting with objects are disturbed.
Preventing Astereognosis
Patients are usually recommended sensory re-education exercises to better their deficits. These exercises involve providing a range of tactile or touch stimuli that help restore the feeling in their sensory areas. The exercises include exploring the texture of different surfaces, distinguishing between different shapes, textures, weights, and temperatures through touch, and identifying various objects by touch. Patients repeat these exercises in a gradual manner, gradually increasing the level of difficulty. They can use their vision or their unaffected hand to provide feedback on the exercises. Also, they are often given personalized exercises to do at their homes, catering to their specific needs and progress.
