carpal tunnel syndrome
Meaning of carpal tunnel syndrome: The little finger is spared because a different nerve supplies it, and that pattern is the most useful clue available.
Definition of carpal tunnel syndrome
Carpal tunnel syndrome is the set of symptoms produced when the median nerve is squeezed inside the carpal tunnel, a narrow passage at the wrist bounded by wrist bones and roofed by a stiff band of ligament. Numbness, tingling and burning affect the thumb, index and middle fingers, often waking a person at night, and grip weakens as the compression advances.
What is the tunnel, and what is inside it?
A channel at the base of the palm, floored and walled by the small bones of the wrist and roofed by a thick ligament stretched across them. Nine tendons that bend the fingers and thumb pass through it, and the median nerve travels with them. The space cannot expand, since bone surrounds three sides and the roof barely stretches. Anything swelling the contents or narrowing the channel therefore raises pressure on the softest structure present, which is the nerve. Squeezing first interrupts the blood supply within the nerve, producing intermittent tingling, and only later damages the insulating sheath and the fibers themselves, at which point numbness becomes constant and the muscle bulk at the base of the thumb wastes away.
Why is it worse at night?
Most people sleep with the wrist bent, and pressure inside the tunnel rises steeply when the wrist is flexed or extended rather than held straight. Fluid also redistributes on lying flat, adding to the volume within the channel. The result is paresthesia, an abnormal tingling or burning sensation, waking a person in the early hours and often eased by shaking the hand or letting it hang down. That nocturnal pattern is characteristic enough to be among the first things asked about.
What makes it more likely?
| Factor | How it acts |
|---|---|
| Pregnancy | Fluid retention swelling the tunnel contents |
| Underactive thyroid | Tissue swelling from deposited material |
| Rheumatoid arthritis | Inflamed tendon sheaths taking up space |
| Acromegaly | Enlarged soft tissue and bone narrowing the channel |
| Ganglion cyst or old wrist fracture | Direct narrowing of the passage |
| Forceful repetitive hand work with vibration | Swelling of the tendons within the tunnel |
Numb fingers do not always originate at the wrist. Pressure on a nerve root in the neck gives a similar distribution but usually with neck pain and a different pattern of weakness, while compression of the ulnar nerve at the elbow affects the little finger and the adjoining half of the ring finger, territory the median nerve does not supply.
Also known as
Used in a sentence
Nerve conduction studies confirmed carpal tunnel syndrome on the dominant side.
Good to know
The median nerve supplies the thumb, index, middle and half the ring finger, so numbness that includes the little finger points away from the carpal tunnel and toward the ulnar nerve or the neck.
Word origin
Where “carpal tunnel syndrome” comes from
Carpal comes from the Greek karpos, meaning the wrist.