Occurrence of bifid median nerve in healthy and carpal tunnel syndrome patients.

We investigated the possible association between median nerve morphology and carpal tunnel size, hand side and nerve conduction measurements. The study included a patient group (n = 58; 44 women) with idiopathic carpal tunnel syndrome (CTS) in 100 hands and a control group of healthy volunteers (n = 56, 112 hands; 44 women). The following data were recorded: (1) median and ulnar motor and sensory nerve conduction parameters (2) ultrasonographic dimensions of the carpal tunnel inlet area (CTAin) and inlet area of the median nerve. The prevalence of bifid median nerve was 19% in the CTS hands and 13.3% in the control group. Bilateral bifid nerve was detected in 7 subjects and unilateral in 23, with no side or sex preponderance. The median nerve area was larger in the participants with single than those with bifid median nerve. No correlation was found between CTAin and median nerve area for single or bifid nerves in controls or patients. It was concluded that bifid median nerve was not a rare variation. We could not, however, support its etiological relation to CTS. Ultrasonographic examination of the carpal tunnel region supplementing neurophysiology provided a reliable means to detect median nerve size and morphology. CLINICAL TRIAL REGISTRATION NUMBER: 84; 5/3/15.

Generation of Repeater F Waves in Healthy Subjects.

PURPOSE: F waves identical in latency, size, and shape, known as repeater F waves, have been observed occasionally in normal motor conduction recordings. The purpose of this study was to examine the occurrence and characteristics of repeater F waves in healthy subjects under different testing conditions, aiming to selectively excite lower and higher threshold motor fibers. METHODS: Sessions of 40 traces were recorded from the ulnar nerve in 12 volunteers, applying/using supramaximal, submaximal stimuli (intensity able to elicit 30% and 60% of the maximum compound muscle action potential amplitude), and a collision technique. Repeater F waves were identified and their numbers and relative frequency were estimated. For this purpose, a custom-designed software program was developed, to avoid misjudgments of simple visual inspection. RESULTS: Repeater occurrence was significantly higher using 30% submaximal intensity compared with the standard supramaximal stimulation. There was an inverse significant association between repeater index and overall F wave quantity. Repeaters' latency, amplitude, and duration measurements were within the ranges of the nonrepeaters. CONCLUSIONS: We herein showed that in healthy subjects the presence of repeater F waves might increase, when stimulation conditions other than standard single, supramaximal impulses were used. The frequency of repeaters was dependent on the overall F wave persistence, but there was no evidence to support a relationship with the type of motoneurons that was preferentially stimulated.