[Sample size for the estimation of F-wave parameters in healthy volunteers and amyotrophic lateral sclerosis patients].

Objective: The study aimed to investigate whether sample sizes of F-wave study differed according to different nerves, different F-wave parameters, and amyotrophic lateral sclerosis(ALS) patients or healthy subjects. Methods: The F-waves in the median, ulnar, tibial, and deep peroneal nerves of 55 amyotrophic lateral sclerosis (ALS) patients and 52 healthy subjects were studied to assess the effect of sample size on the accuracy of measurements of the following F-wave parameters: F-wave minimum latency, maximum latency, mean latency, F-wave persistence, F-wave chronodispersion, mean and maximum F-wave amplitude. A hundred stimuli were used in F-wave study. The values obtained from 100 stimuli were considered "true" values and were compared with the corresponding values from smaller samples of 20, 40, 60 and 80 stimuli. F-wave parameters obtained from different sample sizes were compared between the ALS patients and the normal controls. Results: Significant differences were not detected with samples above 60 stimuli for chronodispersion in all four nerves in normal participants. Significant differences were not detected with samples above 40 stimuli for maximum F-wave amplitude in median, ulnar and tibial nerves in normal participants. When comparing ALS patients and normal controls, significant differences were detected in the maximum (median nerve, Z =-3.560, P <0.01; ulnar nerve, t =5.019, P <0.01; tibial nerve, Z =-2.475, P <0.05; peroneal nerve, Z =-2.088, P <0.05)and mean F-wave latency (median nerve, Z =-3.243, P <0.01; ulnar nerve, t =3.876, P <0.01; tibial nerve, Z =-2.206, P <0.05; peroneal nerve, Z =-2.205, P <0.05)in all four nerves, F-wave chronodispersion ( Z =-3.152, P <0.01)in the ulnar nerve, F-wave persistence in the median ( Z =6.139, P <0.01)and ulnar nerves( Z =5.350, P <0.01), mean F-wave amplitude in the tibial nerve( t =2.981, P <0.01), maximum F-wave amplitude in the ulnar ( Z =-2.134, P <0.05)and tibial nerves ( t =2.746, P <0.01)with 20 stimuli; for chronodispersion in tibial nerve ( t =2.551, P <0.05)100 stimuli, for chronodispersion in peroneal nerve ( Z =-2.086, P <0.05)80 stimuli, for F-wave persistence in tibial nerve ( Z =2.119, P <0.05) 60 stimuli, for mean F-wave amplitude in ulnar ( Z =-2.552, P <0.05)and peroneal nerve ( Z =-2.228, P <0.05)40 stimuli, for maximum F-wave amplitude in peroneal nerve ( t =2.693, P <0.01)60 stimuli were necessary to detect differences. Conclusions: Sample sizes of F-wave study differed according to different nerves, different F-wave parameters , and ALS patients or healthy subjects.