Carpal tunnel syndrome is a narrowing of the median nerve in the region of the carpal portion of the wrist. At this site, the median nerve runs together with nine flexor tendons within a tunnel bounded by the carpal bones and the approximately 3 cm-wide ligament, retinaculum flexorum.

Epidemiology

Carpal tunnel syndrome is the most common compression syndrome of the peripheral nerves and occurs to a clinically significant extent requiring treatment in 5-10% of the adult population¹. Carpal tunnel syndrome occurs in middle age and is 4x more common in women than in men². In over 50% of cases, carpal tunnel syndrome is bilateral³.

Pathophysiology

Pressure conditions in the carpal tunnel correlate with the following pathophysiological phenomena⁴:

Pressure (mmHg)	Correlation
< 20 mmHg	Normal
20-30 mmHg	Venous flow slowed
30 mmHg	Axonal transport impaired
40 mmHg	Sensory & motor dysfunction
60-80 mmHg	Cessation of blood flow

Symptoms

Typical symptoms of carpal tunnel syndrome are nocturnal pain or painful paresthesias in one or both hands. These paresthesias may also occur during the day with certain hand positions. Shaking the hands or changing position leads to an improvement in symptoms. As the disease progresses, permanent dysesthesias/hypesthesias and atrophy of the thenar eminence occur⁵.

Diagnosis

The gold standard for detecting carpal tunnel syndrome is measurement of nerve conduction velocity.

Nerve conduction velocity

The following table of distal nerve conduction velocity through the carpal tunnel is based on the assumption of normal proximal nerve conduction velocity⁶.

Severity	Sensory latency (mSec)^a</sup>	Sensory amplitude (mcV)	Motor latency (mSec)^b</sup>	Motor amplitude (mV)
Normal	< 3,7	> 25	< 4,5	> 4
Mild	3,7 - 4,0		4,4 - 6,9
Moderate	4,1 - 5,0		7,0 - 9,9
Severe	> 5 or not measurable		> 10

^{a</sup>: Measurement to the index finger. Sensory latency is measured to the peak of the waveform. <br /> ^{b</sup>: Measurement of the abductor pollicis brevis muscle}}

Differential diagnosis

Relevant differential diagnoses for carpal tunnel syndrome include C6 cervical radiculopathy and polyneuropathy⁷.

Conservative treatment

In the early stage of carpal tunnel syndrome, when only nocturnal paresthesias are present, conservative treatment with wrist splints worn at night, short-term oral administration of corticosteroids, and local corticosteroid infiltration into the carpal canal may be considered⁸.

References

Kretschmer, Thomas, Gregor Antoniadis, and Hans Assmus. Nervenchirurgie. Springer Berlin Heidelberg, 2014. ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩
Handbook of Neurosurgery. Greenberg M, ed. 9th Edition. New York: Thieme; 2019. ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩