Sensory examinations are inherently subjective, both in the manner in which they are performed by an examiner and in the responses the examinee may report. While more of a diagnostic technique than an imaging technique, Quantitative Sensory Testing (QST) can aid in the diagnosis of pain syndromes by standardizing techniques of examination and evaluation. It is defined in its name: a means to perform sensory testing in a quantitative manner, rather than a subjective and qualitative manner. It is loosely analogous to the hearing exam performed in elementary school where fixed stimuli are given and response noted. Unfortunately, QST tests the entire sensory axis rather than localizing the pathology (Gruener and Dyck 1994). Viewing the results in the context of other available signs and symptoms helps pinpoint pathology.
The goal of QST is to standardize the stimuli and create a consistent algorithm for gauging the response in a manner that is reproducible between exams and patients (Gruener and Dyck 1994). QST devices test either vibration or thermal stimuli (Shy et al. 2003). There are two ways to apply such stimuli: (1) by gradually increasing the strength of stimulus in a continuous fashion until a response is detected or (2) applying fixed strength of stimulus for a specific time and noting absence or response (analogous to a hearing exam). Both methods of assessment have strengths and weaknesses; but that no single method is ideal points to the inherent subjectivity of human responses and this method of testing. As a result, concerns have been raised that subject response variability makes this test not entirely reproducible or appropriate for medico-legal disputes to assess malingering (Shy et al. 2003).
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