[Carpal tunnel syndrome. Results of electrodiagnostic studies.]

The results of electrodiagnostic studies on 557 hands of 383 patients with the clinical diagnosis of carpal tunnel syndrome (CTS) are described. History taking, examination and electrodiagnostic studies were performed by the same neurologist (MPH). The diagnostic sensitivity for the distal motor latency (DML) was 68%, while the sensitivity for the distal sensory latency (DSL) was 77% and the combined sensitivity for these parameters was 83%. With various "unconventional" studies 91% of hands were diagnosed with CTS. From our results the cause for slowing of median motor nerve conduction velocity (m-MNCV) in the forearm seems to be both demyelination at the wrist and axonal degeneration. However, hands with denervation had more slowing of m-MNCV in the forearm than hands without denervation. Hands with clumsiness, subjective weakness, objective weakness and thenar atrophy, compared to hands without these symptoms and signs, had a higher estimate of the relative risk of abnormal DML, DSL, compound motor action potential (CMAP), compound sensory nerve action potential (CSNAP), m-MNCV in the forearm and electromyography (EMG) on abductor pollicis brevis (APB) and from less severe to more severe motor symptoms and signs the odds ratio steadily increased for all tested parameters. Hands with Phalen's sign had more prolonged DML and abnormal EMG on APB compared to hands without Phalen's sign but other test parameters showed no difference. No difference could be found for any test parameters between hands with or without Tinel's sign, neither between hands without pain or with pain, whether in the hand or more proximally in the upper extremity, nor between hands of 150 patients with bilateral CTS who claimed one hand worse than the other. In hands with decreased pin prick, decreased touch or hyperesthesia, compared to hands with a normal sensory examination, the DML, CMAP, and EMG on APB were significantly more often abnormal but no difference was found for any of the sensory conduction test parameters. With increasing duration of symptoms there were significantly more abnormal results for all tested parameters except CMAP, especially when the symptoms had lasted for more than 10 years.