QST TECHNIQUE
What is QST?
Quantitative sensory testing (QST) is a method through which sensory nerve function is quantitatively measured, based on responses of the subject. The peripheral sensory nervous system responds to specific stimuli of specific modality and intensity in a specific manner, which is well-known through many decades of research into human sensation.
QST is a validated, reliable, and sensitive measure for peripheral and central sensory function.
It is non-invasive and mostly not painful for the subject and may be easily conducted by a health professional or researcher.
Many QST studies along the years have collected data from healthy subjects from several age groups, gender-affiliations, and ethnicities.
This normative data forms a great source for comparison of results of standardized QSTs, in order to discriminate between normal sensory function and sensory deficit. Medoc’s devices have been used extensively to perform QST in the past 30 years and have laid the groundwork for such comparisons.
What information does QST provide?
Thermal QST provides information about the function of small diameter unmyelinated (C fibers) and thinly myelinated (A-delta fibers) nerve fibers for which no nerve conduction test, or other objective tests exist.
Small fiber nerve damage can manifest itself in thermal hypoesthesia (raised perception thresholds) or hyperalgesia (lowered pain thresholds).
Vibratory QST can indicate damage to large myelinated nerve fibers. Deficits in these nerve fibers will be apparent in vibratory hypoesthesia (raised vibration detection thresholds).
QST can also be indicative of central pain sensitization, through lowered pain thresholds found remotely from an affected body area; or through altered Dynamic QST measures like Conditioned Pain Modulation or Temporal Summation.
Watch the thermal QST webinar:
In this webinar, we demonstrate various modalities of static and dynamic QST, such as sensory and pain threshold tests, conditioned pain modulation (CPM), temporal summation, and more.
What added value does QST give?
QST, together with the clinical anamnesis, can solidify the diagnosis of peripheral neuropathy, by adding a quantitative measure to the patient’s narrative [i][ii].
In case of peripheral neuropathy, specifically small fiber or mixed-fiber neuropathy, QST can be informative to whether there is deficit of small nerve fibers and the extent of this, in the absence of objective functional tests for these types of fibers.
QST can also complete the picture as a marker of sensory dysfunction in chronic pain syndromes [iii][iv][v][vi].
There is evidence that QST may indicate pre-clinical sensory nerve damage in Diabetic neuropathy, in a stage where it may still be reversible [vii][viii][ix].
How is QST conducted?
Generally when using QST, a stimulus is offered and the subject stops it, as soon as the required level of sensation is achieved.
A significant body of normative data has been gathered along the years with Medoc devices using standardized protocols allowing comparison of test results to people of the same age/gender per body site. This information grants insight into whether test results are within the normal range or deviant.
For these reasons it’s important for the test to be conducted in a standardized fashion in a comfortable environment for the subject (room temperature, position of the participant), with clear instructions, and minimal distractions.
In Thermal QST, a probe is used called a thermode. The thermode consists of a metal plate that on command of the device’s proprietary software will increase or decrease temperature in a controlled rate. Usually the test is started with a neutral temperature as close as possible to the test subject’s external body temperature. The test is typically stopped through a “response unit” by the subject who indicates that a specific sensation has been reached. This method is called the Method of Limits. Both TSA2 and Q-Sense devices can be used for thermal QST procedure.
In QST for pressure pain, the AlgoMed device’s round small probe is placed on the tested body part. The pressure is gradually increased by the operator, measured and guided by the software for standardization.
In Vibratory QST, the tested body site rests on a small probe that on command of the software can be programmed to either vibrate at high amplitude and decreasing, or vibrate a low amplitude and increasing.
The new VSA2 has a high accuracy and resolution of results, as well as the option to differentially test different receptors using different frequencies that you can choose from.
What is Dynamic QST?
The mention of Dynamic QST often refers to measuring central nervous system pain processing, by applying a combination of (supra-threshold) pain stimuli and following the behavioral response along and after the stimuli application.
Examples of dynamic QST are;
Temporal summation (TS), Conditioned Pain Modulation (CPM), and Offset Analgesia (OA).
Read more about them on the For Researchers page.