In quantitative sensory testing, certain methods may lead to incorrect estimates of vibratory (VDT), cool (CDT), or warm (WDT) detection thresholds. We have shown that the specific forced-choice algorithm of testing employed in our Computer-Assisted Sensory Examination (CASE IV) system, when compared with other tests of nerve dysfunction, provides accurate and reproducible estimates of these thresholds. Because this forced-choice algorithm is time consuming and performance might be made worse by drowsiness or boredom, we explored other algorithms that might provide estimates of threshold similar to those obtained with the forced-choice algorithm, but more quickly. In a trial of 25 healthy subjects and 25 patients with neuropathy, the 4, 2, and 1 stepping algorithm with null stimuli, based in part on comparative data from computer simulation and insights from patient decision making, provides an accurate estimate of threshold. On average, the time needed for forced-choice testing was 12.8 +/- 2.9 minutes (mean +/- SD). For 4, 2, and 1 stepping testing, it was 2.7 +/- 2.5 minutes--a large saving of time. Since null stimuli were employed in the 4, 2, and 1 stepping algorithm, it was possible to monitor for spurious responses and repeat the test if they occurred at an excessive rate. The algorithm appears to be sufficiently robust to be recommended for clinical use and for some controlled clinical and epidemiologic trials.

We recently found that vibratory detection threshold is greatly influenced by the algorithm of testing. Here, we study the influence of stimulus characteristics and algorithm of testing and estimating threshold on cool (CDT), warm (WDT), and heat-pain (HPDT) detection thresholds. We show that continuously decreasing (for CDT) or increasing (for WDT) thermode temperature to the point at which cooling or warming is perceived and signaled by depressing a response key ("appearance" threshold) overestimates threshold with rapid rates of thermal change. The mean of the appearance and disappearance thresholds also does not perform well for insensitive sites and patients. Pyramidal (or flat-topped pyramidal) stimuli ranging in magnitude, in 25 steps, from near skin temperature to 9 degrees C for 10 seconds (for CDT), from near skin temperature to 45 degrees C for 10 seconds (for WDT), and from near skin temperature to 49 degrees C for 10 seconds (for HPDT) provide ideal stimuli for use in several algorithms of testing and estimating threshold. Near threshold, only the initial direction of thermal change from skin temperature is perceived, and not its return to baseline. Use of steps of stimulus intensity allows the subject or patient to take the needed time to decide whether the stimulus was felt or not (in 4, 2, and 1 stepping algorithms), or whether it occurred in stimulus interval 1 or 2 (in two-alternative forced-choice testing). Thermal thresholds were generally significantly lower with a large (10 cm2) than with a small (2.7 cm2) thermode.(ABSTRACT TRUNCATED AT 250 WORDS)

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Estimates of vibratory detection threshold may be used to detect, characterize, and follow the course of sensory abnormality in neurologic disease. The approach is especially useful in epidemiologic and controlled clinical trials. We studied which algorithm of testing and finding threshold should be used in automatic systems by comparing among algorithms and stimulus conditions for the index finger of healthy subjects and for the great toe of patients with mild neuropathy. Appearance thresholds obtained by linear ramps increasing at a rate less than 4.15 microns/sec provided accurate and repeatable thresholds compared with thresholds obtained by forced-choice testing. These rates would be acceptable if only sensitive sites were studied, but they were too slow for use in automatic testing of insensitive parts. Appearance thresholds obtained by fast linear rates (4.15 or 16.6 microns/sec) overestimated threshold, especially for sensitive parts. Use of the mean of appearance and disappearance thresholds, with the stimulus increasing exponentially at rates of 0.5 or 1.0 just noticeable difference (JND) units per second, and interspersion of null stimuli, Békésy with null stimuli, provided accurate, repeatable, and fast estimates of threshold for sensitive parts. Despite the good performance of Békésy testing, we prefer forced choice for evaluation of the sensation of patients with neuropathy.

Twenty individuals underwent quantitative sensation testing (QST) before and after 1 dose of aspirin, acetaminophen, or acetaminophen with codeine to determine the effect of analgesics on QST results. There was no significant change from baseline when mean QST results after placebo were compared to mean QST results after analgesics. We conclude that the effect of small doses of simple analgesics on QST results is either not present or is too small to necessitate withholding analgesics before sensory testing.