Ulnar and Median Nerve Abnormalities in Carpal Tunnel Syndrome

Nerve compression underlying carpal tunnel syndrome (CTS) results in an increase in the threshold of superficial sensation in the area supplied by the median nerve, which is a mixed nerve dominated by sensory fibres. The distribution of sensory symptoms is strongly dependent on the degree of electrophysiological dysfunction of the median nerve. The association between carpal tunnel syndrome and ulnar nerve entrapment at wrist level is still unclear. Patho-logical processes leading to median neuropathy in CTS may affect ulnar nerve motor and sensory fibers in the Guyon canal. This may explain the extra-median spread of sensory symptoms in CTS patients.

The study involved 88 patients (104 hands), with 70 women (83 hands) and 18 men (21 hands) aged between 25 and 77 years. 50 age- and sex-matched subjects without carpal tunnel syndrome were used as a control group. The diagnosis of carpal tunnel syndrome was made according to the criteria of the American Academy of Neurology 1993 guidelines. Based on the results of an ENG trace evaluating the degree of conduction disturbances in the median nerve, the patients were classified to one of three severity subgroups. The threshold of sensory excitability to pulsed current was determined in a test with single 100 ms rectangular pulses.

1. The threshold of sensation in the fingers innervated by the median and ulnar nerve is significantly lon-ger in patients with CTS than in controls. 2. Surgical treatment decreases the threshold of sensation in the fingers innervated by the median nerve. 3. Surgical treatment does not decrease the threshold of sensation in the fingers innervated by the ul-nar nerve. 4. The preoperative and postoperative threshold of sensation in the fingers innervated by the median and ulnar nerve is significantly longer in patients with severe carpal tunnel than in mild and moderate cases.