Paresthesia is an abnormal sensation, often described as a tingling sensation, or likened to "pins and needles" or electricity, pricking, or even crawling (formication), i.e., positive sensory symptoms. The sensation is not pleasant but nor is it painful (cf. dysesthesia). Some patients may describe this sensation as "numbness" or "deadness", in which case care needs to be taken to differentiate it from anesthesia (i.e., a negative phenomenon). Some authorities reserve the term for spontaneous rather than evoked positive sensory phenomena, as a distinction from dysesthesia.
Paresthesia is a feature of neuropathy, and may occur in the distribution of a compressed or entrapped nerve, perhaps reflecting the mechanosensitivity of nerves in this situation (e.g., Phalen’s sign, Tinel’s sign). Paresthesia is a more reliable indicator of the diagnosis of neuropathy than pain. Paresthesia may also be provoked by hyperventilation (especially perioral, hands and feet [acroparesthesia]). Central lesions may also produce paresthesia (e.g., Lhermitte’s sign).
Larner AJ. Missed diagnosis of vitamin B12 deficiency presenting with paresthetic symptoms. International Journal of Clinical Practice 2002; 56: 377-378