Quantitative sensory testing: methodology, applications, and future directions

Quantitative sensory testing (QST) is based on well-developed psychophysical methods that define not only the stimulus (type, characteristics, quantity, presentation, testing format, and environment) but also the response (form and analysis). With the availability of personal computers, transducers, electronic circuitry, and specially written software, it became possible to develop systems that delivered physical stimuli with waveforms that were precisely defined, quantitated, and graded over a broad range of magnitudes, and capable of eliciting unitary sensations. Specific algorithms of testing and finding threshold could now be programmed for exact and sequential error-free testing. Results could also be efficiently and accurately printed out and compared with normal values with consideration of modality, site, gender, height, and weight. QST's main application is in quantifying modality-specific detection thresholds (and some suprathresholds also) in health (by site, side, development, aging, and other) and in disease (involving sensory receptors, nerve fibers, central nervous system tracts, or cerebral association areas), allowing it to play the unique role of standardizing the clinical examination. Used to identify modality-specific sensory loss it can, for example, be correlated with the compound action potential of sural nerve in vitro and with the number and sizes of fibers. In detecting patterns of sensory abnormality, it can also suggest the presence of specific diseases and be used to follow the course of sensory loss. Finally, because it is the best approach to detect, characterize, and quantitate sensory abnormality, it is useful both in epidemiologic and controlled clinical trials. Although our review focuses especially on the approaches and system we have developed, other systems using standardized approaches are available allowing the evaluation of vibratory (VDT), cooling (CDT), and warming (WDT) detection thresholds and visual analog scaling of heat pain (HP VAS).