Abstract-Objective:This assessment evaluates the clinical utility, efficacy, and safety of quantitative sensory testing (QST). Methods: By searching MEDLINE, Current Contents, and their personal files, the authors identified 350 articles. Selected articles utilized computer operated threshold systems, manually operated threshold systems, and electrical threshold devices. The authors evaluated the use of normal values and the degree of reproducibility between the same and different systems. Articles were rated using a standard classification of evidence scheme. Results: Because of differences between systems, normal values from one system cannot be transposed to others. Reproducibility of results was also an important concern, and there is no consensus on how it should be defined. The authors identified no adequately powered class I studies demonstrating the effectiveness of QST in evaluating any particular disorder. A number of class II and III studies demonstrated that QST is probably or possibly useful in identifying small or large fiber sensory abnormalities in patients with diabetic neuropathy, small fiber neuropathies, uremic neuropathies, and demyelinating neuropathy. Conclusions: QST is a potentially useful tool for measuring sensory impairment for clinical and research studies. However, QST results should not be the sole criteria used to diagnose pathology. Because malingering and other nonorganic factors can influence the test results, QST is not currently useful for the purpose of resolving medicolegal matters. Well-designed studies comparing different QST devices and methodologies are needed and should include patients with abnormalities detected solely by QST. NEUROLOGY 2003;60:898 -904 Quantitative sensory testing (QST) systems have been developed to assess and quantify sensory function in patients with neurologic symptoms or in those at risk of developing neurologic disease. QST measures the detection threshold of accurately calibrated sensory stimuli. Vibratory, thermal, or painful stimuli are often chosen because they relate to distinct neuroanatomic pathways with discrete fiber populations.1-3 It should be appreciated, however, that natural stimuli rarely activate single types of receptors but rather activate different combinations of receptors. 1Quantitative sensory tests are psychophysical in nature, requiring cooperation from the patient. While the sensory stimulus is an objective physical event, the response represents the subjective report from a patient or control subject. If abnormal, the result may signal dysfunction anywhere along the sensory pathway between the receptor apparatus, the primary sensory cortex, and the association cortex. Furthermore, psychological factors figure prominently in sensory function perception. Thus, QST differs from nerve conduction and evoked potential testing in which the stimulus generates an evoked response that is generally independent of cooperation from the subject. 4QST devices. QST systems are separable into devices that generate specific physical...

Repetitive firing in axons can lead to their subexcitability and reduced conduction velocity, due to prolonged hyperpolarization (Gasser, 1935;Bergmans, 1970;Bostock & Grafe, 1985). Such activity-dependent changes in membrane potential and conduction velocity are much more pronounced in unmyelinated fibres than in myelinated ones (Ritchie & Straub, 1957;Grafe et al. 1997), and have been used in microneurographic recordings from humans as a 'marking' technique for C fibres activated by natural stimuli (Hallin &

SUMMARY1. Intraneural microstimulation (i.n.m.s.) was performed in awake human volunteers, using tungsten micro-electrodes inserted into median and ulnar nerve fascicles supplying the skin of the hand. The same electrodes were used alternatively to record impulse activity from single nerve fibres at the i.n.m.s. sites.2. Monitoring occasionally, with a proximal electrode, the impulse traffic evoked by i.n.m.s. distally in the same fascicle, established that the stimulation procedure could be made selective enough to activate single myelinated fibres in isolation, while also permitting multifibre recruitment.3. Monitoring propagated impulses also established that i.n.m.s. of a single myelinated fibre supplying a low-threshold mechanoreceptor in the hand might evoke an elementary sensation. Such sensations were fully endowed with cognitive attributes amenable to psychophysical estimation: quality, magnitude and localized projection.4. Psychophysical tests were made during i.n.m.s. at intraneural sites where single-unit activity was recorded from classified RA, PC, SA I or SA II mechanoreceptors. Changes in excitability of the nerve fibre of an identified unit, induced by further i.n.m.s., certified that the recorded unit had been stimulated during psychophysical tests.5. Comparing physical location of the receptive field of a recorded unit and localization of the projected field of the corresponding elementary sensation, revealed that either predicted the other accurately. This further assisted identification of the unit activated by i.n.m.s.6. The type of a recorded unit and the quality of the elementary sensation evoked by its activation were also reciprocally predictive. RA units evoked intermittent tapping, PC units vibration or tickle and SA I units evoked pressure. SA II units evoked no sensation when activated in isolation.7. Afferent impulse frequency determined magnitude of pressure in the SA I system, and frequency of vibration in the PC system. In the RA system, stimulation frequency determined frequency of tapping-flutter-vibration sensation at relatively low rates and subjective intensity of sensation at high rates.

The quantitative somatosensory thermotest (QST) assesses the function of afferent channels concerned with sensory submodalities served by small calibre fibres. Measured ramps of ascending or descending temperature are applied to the skin through a Peltier contact thermode, and detection thresholds are recorded as the subject signals the onset of a particular sensation. The present study describes underlying principles, methodological aspects and normal reference values for the QST. In patients, measurement of thresholds for cold sensation, warm sensation, cold-induced pain and heat-induced pain, applied to 465 individuals, yielded 13 abnormal patterns segregated into three main groups: (i) thermal (cold or warm) hypoaesthesia; (ii) thermal hyperalgesia (abnormally reduced threshold for cold and/or heat induced pain); (iii) thermal hypoaesthesia combined with thermal hyperalgesia. Critical analysis of these results yielded a number of observations of general relevance: (i) thermal specific (warm or cold) hypoaesthesia and thermal (heat or cold) hyperalgesia may occur in the absence of hypoaesthesia for tactile submodalities served by large calibre afferents; (ii) cold hypoaesthesia and warm hypoaesthesia may dissociate from each other; (iii) thermal pain hyperalgesias may occur in the absence of hypoaesthesias for specific cold or warm sensations; (iv) cold hyperalgesia and heat hyperalgesia may dissociate from each other. Thus, a negative routine sensory examination and unimpaired sensory nerve action potentials do not exclude possible somatosensory dysfunction. Furthermore, while most methods of sensory testing only document normality or deficit, the QST permits additional documentation of hyperalgesia, a positive sensory phenomenon that implies unusual pathophysiologies such as sensitization of receptors, central hyperexcitability, disinhibition or, possibly, ectopic nerve impulse discharge. This psychophysical test does not specify the level within afferent channels, between skin and brainmind, where the abnormality resides. It is recommended that the QST for all four thermal specific and thermal pain functions be incorporated in routine neurological assessment.