Diagnositic evaluation of F-wave inversion in carpal tunnel syndrome

The contribution of motor nerve conduction studies to the electrophysiological diagnosis ofcarpal tunnel syndrome (CTS) is limited. However, it has been put forward that the sensitivityof the prolongation of the median F-wave latency compared to ulnar F-wave latency (F-waveinversion) is comparable to sensory nerve conduction studies. In order to investigate thecontribution of this interesting observation to the diagnosis of CTS, we determined the normalupper limit of this measurement in normal individuals and assessed its specificity. In definiteand probable CTS groups the sensitivity of the method was also tested. Moreover, its relationwith physiological variables such as age and height was calculated. We retrospectivelystudied the electronic database of the Clinical Neurophysiology Laboratory of the NeurologyDepartment of Gazi University Faculty of Medicine and selected individuals withoutsymptoms related to CTS and normal nerve conduction studies (normal subjects). Anothergroup was formed consisting of individual s with definite clinical and electrophysiologicalevidence of CTS (definite CTS). A different group was composed of subjects withmanifestations suggestive of CTS (probable CTS). All subjects underwent motor and sensorynerve conduction studies of the median nerve, as well as the F-wave latency measurements ofthe ulnar nerve. Clinical and electrophysiological findings were staged according to theclassification of the Italian CTS Study Group. The specificity of F-wave inversion was foundto be 100%. This parameter showed the highest sensitivity among other motor variables. Onthe other hand, in the definite CTS group its sensitivity was 63.5%, whereas the sensitivity ofthe method was found to be 66.5% in the probable CTS group. In the latter group, amongpatients with normal sensory studies, 60% demonstrated F-wave inversion. However, sensorynerve conduction studies were abnormal in 83.5% of patients of the probable CTS group.Neither age (r=0.01, p=0.97) nor height (r=0.09, p=0.629) was related to inversion of the Fwave.No association was found with the neurophysiologic grading and F-wave inversion