Sensory testing involves the evaluation of a patient's perception in an effort to assess the integrity of the peripheral nervous system. There are many sensory receptors in the human body that provide information to the brain concerning an individual's surroundings. The information from sensory receptors helps the human being move and interact within the environment. For example, information from various sensory organs such as the eyes, vestibular (inner ear), and light touch are all integrated and organized by the brain to help the body complete safe and efficient movement. If sensory impairment is present, the patient's movement will likely be affected, making common tasks cumbersome and even dangerous. Therefore, individuals with possible sensory impairment need to have a full sensory evaluation to assess the integrity of sensation.
There are many pathologies that can cause impairments in sensation. Injury or disease can compromise the integrity of a nerve and thus impair sensory function. Peripheral neuropathy is a broad classification that describes disease or dysfunction of a peripheral nerve. A peripheral neuropathy can be acquired or inherited.
Acquired peripheral neuropathy
A common acquired peripheral neuropathy is Guillain-Barre syndrome. This syndrome is usually considered an autoimmune disorder, but the etiology (cause) is unknown. Guillain-Barre syndrome is classified as a myelinopathy where the myelin sheath (an insulating wrapping which surrounds the axons of many nerves) disintegrates. In this disorder there is marked weakness and sensory impairment on both sides of the body. Two other types of acquired peripheral neuropathy are alcoholic and diabetic neuropathies. Alcoholic neuropathy is due to alcoholism and diabetic neuropathy is due to diabetes, a metabolic disease. In alcoholic neuropathy, sensory and motor losses are typical, especially in the feet and lower legs. The actual cause is unknown, but may be due to the toxic effects of alcohol on the nervous system. In diabetic neuropathy sensory loss also is prominent, especially in the lower limbs. Other acquired neuropathies can be caused by laceration (e.g., knife injury), crushing injuries to the nerve, or ischemia (a condition characterized by a decreased supply of oxygenated blood ). All can lead to sensory and/or motor impairment by compromising the integrity of the nerve.
Inherited peripheral neuropathy
The most common inherited peripheral neuropathy is Charcot-Marie-Tooth disease. It is a genetic disorder that is categorized by weakness or atrophy of the lower limbs, especially the lower leg and foot.
There are many sensory receptors corresponding to various sensations within the human body. The purpose of sensory receptors is to gather pertinent information on the surrounding environment. Sensory receptors respond to stimuli in the environment, and thus provide valuable information on a person's surroundings. Therefore, the disorders categorized as peripheral neuropathies can impair the gathering and transmission of information. The purpose of sensory testing is to evaluate the proficiency and integration of information from sensory receptors in individuals who have known disease or injury.
Sensory testing gives valuable information to the clinician on an individual's sensation and perception. Care must be taken when performing sensory tests if sensory loss is suspected. Applying increased pressure or heat on an individual who has a sensory deficit may injure the patient. For example, if a patient cannot sense the application of heat, there is a risk that the patient will be burned.
Sensory testing should be done on both sides of the body so that comparisons can be made between sides, that is, affected side versus non-affected side. If there is a deficit noted, it is usually termed absent, diminished, or exaggerated. If there is no deficit, sensation is termed intact.
There are seven common tests used to evaluate sensation and perception. They are: stereognosis, touch and pressure, kinesthesia, proprioception, touch localization, two-point discrimination, and recognition of textures.
Stereognosis refers to the ability of an individual to identify objects placed in his/her hand, while his/her eyes are closed. The individual should be able to identify objects based on size, shape, and texture.
Touch and pressure
Touch can be assessed by gently rubbing a ball of cotton on the surface of the skin to be tested. The clinician's finger can be used to apply pressure to various locations in order to assess pressure sensation. While touch and pressure are being assessed, the subject's eyes should be closed.
This test evaluates the individual's perception of movement specifically related to the limbs. In this test the individual's eyes are closed while the examiner moves the unaffected limb into a position and holds the position. The examiner then asks the individual to move the affected side into the same position.
This test assesses the individual's perception of joint movement rather than position (proprioception). In this test, the examiner moves the unaffected limb and, as the limb is moved, the individual being tested must copy the movement and follow the path with the affected or involved side. This test also is done with the individual's eyes are closed.
While the subject's eyes are closed, the examiner touches different areas on the skin and asks the subject, "Where am I touching?" The subject must verbally identify the location of the examiner's touch.
This test evaluates an individual's ability to discern two points at the same time. While the subject's eyes are closed, the examiner applies point pressure in two spots separated by one to two inches. The examiner asks the subject, "Can you feel two points?" If the subject can discern two points, the examiner moves the points closer together and the test is repeated. This continues until two points cannot be discerned. These results are compared with results from the opposite side.
Recognition of textures
Various textures are placed in the individual's hand, while his/her eyes are closed. The individual must verbally identify the texture. Cotton and sandpaper are examples of items used in this test.
Another testing device, the Weinstein Enhanced Sensory Test (WEST), is primarily used to assess touch sensation. It is a precision instrument that uses hair-like filaments to record pressure or force. The instrument is a safe, valid, and reliable way of recording sensory loss.
Results or outcomes of treatment are variable. Usually the initial severity of the deficit reflects the possible outcome. The greater the deficit, the greater the likelihood of long-term or total impairment.
Health care team roles
Nurses and other allied health team members need to be aware of potential sensory and perceptive disorders and their relationship to function. Early identification of sensory or perceptive impairments may minimize further complications. Physicians, nurses, and allied health professionals, such as occupational and physical therapists, usually perform sensation testing. Nurses are now becoming more familiar with the WEST device and this technology is now available for assessing the feet. This is especially useful for patients with diabetic neuropathy.
Kinesthesia— The ability to perceive where a limb or the body is moving in space. Information about the surrounding environment is processed in the brain and received from muscles, tendons, and joints.
Proprioception— The ability to perceive where a limb or the body is in space. Usually refers to a static situation.
Sensation— Awareness (as of heat or pain) due to stimulation of a sense organ.
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