Variabilità test-retest in soggetti normali ed affetti da sclerosi multipla

Test-retest variability (trv) is a common characteristic of any biological test. In normal subjects Auditory Brainstem Response gives a small trv while this is significantly increased in subjects afflicted with Multiple Sclerosis (MS). Trv evaluation has been included among the "sensitized ABRs", a group of tests able to increase ABR diagnostic capacity. The trvs are analyzed with precise methods, some of which are objective (cross-corelation) some of which are interactive (evaluation of Vth wave latency) at three different stimulation rates: 11, 51 and 81 pulses/s. The purpose of this work was to see whether there was a progressive increase in trv as the possibility of disease increased. Three groups of subjects were used: normal, suspected MS, certain MS. The authors also intended to identify which of the objective and interactive parameters were best suited to trv evaluation and what influence stimulation rate had on the trv itself. The resluts obtained showed a progressive increase in trv, at almost all stimulation rates and for all parameters studied, rangeing from normal subjects to those suspected of MS and finally to those with certain MS. In thecases studied (16 normal subject, 16 definite MS) trv, used as a diagnostic test, was 80% efficient with a 93,3% specificity and 66,7% sensitivity. These values were obtained using both interactive methods (Delta wave, V latency) and objective methods (R(0), delay). The latter has the advantage of eliminating operator related variability. In regard of the different stimulation rates, the overall results, which are rather variable, do not show any significant increase in variability with an increase in the stimulation rate.