numbness
Meaning of numbness: Sensation reduced or absent in an area, which is a different finding from the tingling and pins and needles it is often confused with.
Definition of numbness
Numbness is reduced or absent feeling in part of the body, so touch, temperature or pain is registered weakly or not at all there. It results from interrupted signaling anywhere along the sensory pathway, from the nerve endings in the skin through the nerve trunks and spinal cord to the brain. The area affected often reveals which part of that pathway is involved.
How is numbness different from tingling?
Numbness is a loss: signals fail to arrive, so an area feels dead, wooden or as though covered by a layer. Tingling is the opposite problem, an extra signal generated by nerve fibers firing when nothing has touched the skin, and its medical name is paresthesia. The two often occur together in the same area, which is why both are reported as numbness in ordinary speech. Testing separates them, since an area that is genuinely numb registers touch, pinprick or temperature less strongly than the matching area on the other side.
What does the pattern show?
Where along the sensory route the interruption sits. A single nerve serves a defined patch of skin, a nerve root serves a band, and the brain serves an entire side, so the shape of the numb area maps back to a level.
| Pattern | What it points toward |
|---|---|
| Both feet, later both hands, symmetrically | A generalized nerve disorder striking the longest fibers first |
| One nerve territory, such as the thumb side of the hand | Pressure on a single nerve, as in carpal tunnel syndrome |
| A band around the trunk or a stripe down one limb | Irritation of a nerve root where it leaves the spine |
| One side of the body, face included | The brain or the brainstem |
| A patch arriving over days and settling again | Inflammation within the central nervous system |
Why does a limb go numb after sitting still?
Sustained pressure squeezes a nerve where it runs close to bone or passes through a tight space, and squeezes the small vessels feeding it at the same time. Conduction along the largest fibers fails first, so touch and position sense fade while pain and temperature linger. Once the pressure lifts, the recovering fibers discharge erratically, producing the burst of pins and needles that accompanies the return of feeling. Numbness persisting after the pressure is gone, or arriving in patches over days and settling again, is a different matter, and that relapsing pattern is characteristic of multiple sclerosis.
Also known as
Used in a sentence
Numbness was described over the outer aspect of the lower leg.
Good to know
Numbness is lost sensation while paresthesia is an added abnormal sensation, and although the two are commonly reported under the same word they are distinct findings.