Anomalies of ulnar nerve conduction in different carpal tunnel syndrome stages

Impairment of ulnar sensory fibers at the wrist has recently been documented in moderate/severe carpal tunnel syndrome (CTS). This has been interpreted as a consequence of compressive forces transmitted to Guyon's canal by high pressure in the carpal tunnel or comorbidity between ulnar neuropathy and CTS. The main aim of the present study was to identify any ulnar nerve conduction impairment in the early stages of CTS. The relation between ulnar and median nerve conduction in all CTS severity stages was also assessed. Ulnar nerve sensory conduction at the wrist was investigated in 580 hands with CTS. Significant changes in ulnar nerve conduction were present even in the early stages of CTS. A significant, positive correlation was also found between CTS severity and conduction abnormalities of ulnar sensory fibers. These findings make the hypothesis of comorbidity weak. Based on the above results and on reports of high pressure in Guyon's canal in CTS, ulnar nerve conduction abnormalities may be caused in part by compressive forces progressively transmitted to the canal by increasing pressure in the carpal tunnel with increasing CTS severity. This does not exclude other causative factors such as subclinical traumatic damage acting on median and ulnar fibers.