What Is Quantitative Sensory Testing?

Quantitative Sensory Testing (QST) is a diagnostic tool used in the management of small fiber neuropathy. This is a condition characterized by damage to the small myelinated, or unmyelinated nerve fibers and can cause significant pain and discomfort. Many diseases such as diabetes first affect the small sensory nerve fibers, before they involve the larger sensory and motor fibers. The more commonly performed nerve conduction studies assess damage to the large, myelinated fibers. QST aids in an earlier diagnosis of sensory neuropathy by detecting damage to both the small and large fibers.

Indications for performing Quantitative Sensory Testing include:

• Painful diabetic neuropathy
• Idiopathic distal sensory painful neuropathy
• AIDS-related neuropathy
• Amyloidosis neuropathy
• Paraproteinemia-induced neuropathy
• Paraneoplastic neuropathy
• Neuropathy due to autoimmune conditions

How is Quantitative Sensory Testing performed?

• QST detects the threshold for perception of touch, temperature, pain, and vibration
• A series of one of these stimuli at a time, randomly generated by a computer, is presented to the patient
• The patient is asked to push down a response key when he/she feels the stimulus
• The intensity of the stimulus is adjusted to determine the patient’s threshold for perceiving the sensation
• The entire QST can be performed in one hour

The touch and vibration sensations are transmitted by larger myelinated fibers, the temperature by smaller myelinated fibers, and the pain by unmyelinated fibers. Quantitative Sensory Testing is therefore able to diagnose small fiber neuropathy, before the underlying condition progresses to involve the larger fibers. This can be utilized both in clinical practice and for research purposes. The disadvantage of QST is that it is a psychophysical test that depends on the patient’s response. Due to this, the test results may not be completely objective, although QST is more sensitive than nerve conduction studies and physical examination.