Pallesthesia
Pallesthesia (\ˌpal-es-ˈthē-zh(ē-)ə\), or vibratory sensation, is the ability to perceive
A diminished sense of vibration is known as pallhypesthesia.[3] To determine whether a patient has diminished or absent pallesthesia, testing can be conducted using a tuning fork at 128 Hz by placing it on the skin overlying a bone. This works because bones are good resonators of vibrations.[1]
Receptors
Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles are all encapsulated nerve endings involved in tactile stimulation.
Pathway
The sensory conduction pathway that allows for cognitive recognition of vibration occurs through afferent neurons, also known as sensory neurons. The outside stimulus is a vibration that activates one of the three encapsulated nerve endings based upon where the sensation is felt. The intensity of the vibration must cause the neuron(s) to reach or surpass a threshold in order for an action potential to be propagated. From here, the signal travels through the dorsal column–medial lemniscus pathway.
The pathway is composed of the dorsal column within the
There are three types of neurons in the pathway: first-, second-, and third-order neurons. The first-order neuron is the afferent neuron. It enters the spinal cord through the dorsal root
Testing
Routine clinical tests include quantitative vibratory testing and the Rydel-Seiffer tuning fork test. The typical frequency used for the tuning fork is 128
For accuracy,
Disorders
A benefit of pallesthesia testing is that it can be used to identify disorders within the neural pathways. Because there are few areas in the neural pathway where the sensation and perception of vibration can be disturbed, this testing enables doctors to more accurately diagnose their patients' health. It can help to identify effects of other diseases on the nervous system, such as
Neural disorders
Peripheral nervous system
The peripheral nervous system is composed of afferent and efferent neurons; disorder of these neurons is called peripheral neuropathy. Vibration examination can detect and localize disorders of the peripheral nervous system. A gradual loss of sensation from the toes to the knees is consistent with a peripheral nerve problem, whereas an impairment in perceiving vibration from all extremities is a sign of a posterior column disorder.[1] Impairments classified to the peripheral nervous system and posterior column are indicators of demyelination of afferent neurons from a variety of causes.
Myelopathy
Myelopathy is a disorder within the spinal cord. Compression on the spinal cord by bony projections or a displaced disk in the cervical spine are the most common causes of myelopathy.[7] Inflammation, illness, and neurodegenerative, nutritional, and vascular disorders can also contribute to myelopathy. Quantitative vibratory testing can be used to assess a patient with myelopathy when the examiner detects uniform loss of vibration below a certain spinal level. For example, if the examination is normal from the iliac crest to the knees but pallesthesia is absent from the knees to the toes, this would be consistent with myelopathy.[1]
Central nervous system
The central nervous system is composed of the spinal cord and the brain. Many neurological studies are conducted on patients with lesions. Scientists can learn about the functions of different brain areas by looking at damage to those areas. Thus, studies have been conducted on lesion patients for pallesthesia. A common disease to the central nervous system is multiple sclerosis. In this disease, the immune system attacks the myelin sheath surrounding neurons. Deterioration of the myelin sheath drastically reduces the conduction speed of neurons, thus affecting sensation and motor control of the body. These patients exhibit the largest reduction in pallesthesia. They cannot perceive vibration at 128 Hz; however, studies have shown that 256 Hz can be perceived in young multiple sclerosis patients.[8]
Diabetic neuropathy
Research
From the early 1950s through the 1970s, pallesthesia was used as a research method for many disorders of the sensory system. Scientists hoped to find a new therapy to reconstruct neuronal outputs. They understood that damage to the central nervous system could not be repaired; however, they hoped to rewire the peripheral nervous system to give patients some of their sensation back. One study looked into the effects of pallesthesia on stroke patients.[3] They theorized that sinusoidal stimulation may be an effective therapy; however, the results were inconclusive. It is rare for current research to use pallesthesia because better methods of testing the sensory system have been developed.
See also
References
- ^ a b c d e f g h i j k Campbell, W. W., & DeJong, R. N. (2013). DeJong's the neurologic examination. [electronic resource] William W. Campbell. Philadelphia, PA : Lippincott Williams & Wilkins, c2013.
- ^ "Medical Definition of PALLESTHESIA". www.merriam-webster.com. Retrieved 2018-02-18.
- ^ PMID 5766441.
- ^ a b c d Mark F. Bear, Barry W. Connors, Michael A. Paradiso. Neuroscience: Exploring the Brain, 4th Edition, Baltimore, MD: Lippincott Williams & Wilkins, 2014
- ^ a b Dartmouth. (n.d.). Chapter 7 - Somatosensory Systems. Retrieved December 05, 2017, from [1]
- .
- PMID 18477657.
- PMID 14369331.
- ^ "Diabetic neuropathy - Symptoms and causes - Mayo Clinic". www.mayoclinic.org. Retrieved 2017-12-12.