Pallesthesia
[1] All of these receptors stimulate an action potential in afferent nerves (sensory neurons) found in various layers of the skin and body.
[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.
The Merkel disk receptors are located in the superficial epidermis and in hair follicles, while tactile corpuscles are concentrated heavily in the fingertips.
[1] Merkel disk receptors and tactile corpuscles respond best to low frequencies when producing an action potential.
The pathway is composed of the dorsal column within the spinal cord and the medial lemniscus in the brain stem.
The second-order neuron then carries the information to the ventral posterolateral nucleus of the thalamus and then the somatosensory cortex in the parietal lobe.
[1] Some common areas for testing in the bones are the metatarsals, the tibia, the malleoli, the anterior superior iliac crest, vertebrae in the spinal cord, sternum, clavicle, and the styloid processes of the radius and ulna.
The person may lose some perception of pallesthesia when switching sides, probably due to sensory adaptation, as the receptors require a larger threshold to produce an action potential because of previous stimulation.
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.
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.
Compression on the spinal cord by bony projections or a displaced disk in the cervical spine are the most common causes of 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.
Deterioration of the myelin sheath drastically reduces the conduction speed of neurons, thus affecting sensation and motor control of the body.
A doctor then assesses the damage and places the patient on treatment, which in severe cases may include amputation of a foot or limb.
