Paresthesias
Paresthesias are any sensory abnormality, including numbness.
If nerves, sensory roots, or spinal tracts are damaged or interrupted, the patient may complain of tingling or prickling feelings (like a limb that has fallen asleep), cramp-like sensations, or burning or cutting pain in response to stimulation.
It may be that partially damaged touch, pressure, thermal, and pain fibres become hyperexcitable and generate ectopic impulses, either spontaneously or in response to stimulus-evoked responses.
- touch fibres give rise to tingling or buzzing
- muscle proprioreceptors to pseudocramp
- thermal fibres to hotness and coldness
- A-δ fibres to prickling and pain
Limbs falling asleep
Limbs fall asleep due to nerve compression, most often the ulnar, sciatic, or peronal nerve. This leads to interrupted axonal transport
Patients with chronic fatigue or fibromyalgia can complain of paresthesias, or weakness.
Paresthesias and dysthesias are common with diabetic or alcoholic nutritional neuropathy, mainly affecting the feet ('burning feet') and less often the hands.
Paresthesias can also follow spinal cord injury below the site, with the most common being a dull, burning pain in the lower back and abdomen, buttocks, and perineum.
Paresthesias can also occur due to irritative lesions in the contralateral sensory cortex. Destructive lesions tend to cause impaired sensitivity, affecting perception both qualitatively and quantitatively.