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A quantitative sensory test (QST) defines the skin’s sensory detection thresholds for cold, heat, cold pain and hot pain. These skin sensations are transmitted by thin sensory nerves. In connection with a limb QST, the sensory vibration thresholds for the palms of the hands and soles of the feet are defined, describing the function of thick sensory nerves. In addition, the sensory thresholds of the backs of the hands and the metatarsus are defined. A facial QST defines the sensory and pain thresholds for temperature on the forehead, cheeks and chin, bilaterally.
A small thermistor plate that is cooled down or heated is placed on the skin during the examination. The patient notifies when the skin sensation changes by pushing a button. Next, when the thermistor is cooled down or heated further, the patient notifies the first sensation of pain. These temperatures are then recorded as sensory thresholds for cold, heat, cold pain and hot pain. The sensory threshold measurements for cold and heat are repeated. When the intensity of vibration is increased, the patient notifies the first sensation of vibration. This intensity is then recorded as a sensory threshold for vibration.
A limb QST is most sensitive in verifying diabetic and metabolic small fibre neuropathy (polyneuropathy) of the peripheral nervous system. A facial QST can verify local or generalised small fibre damage. Since the measurements describe the entire sensory system from the skin to the cerebral cortex, nerve damage originating from the central nervous system can also be visible in the sensory thresholds. In addition, sensitisation of sensation and neuropathic pain is detected.
Since the examination requires excellent co-operative skills from the patient, it is important that the patient is well rested and active when he or she comes to the examination. The examination has no permanent after-effects.
A QST test is an additional examination performed after an electroneuromyography (ENMG).