Quantitative Sensory Testing
What is quantitative sensory testing (QST)?
Quantitative sensory testing is a noninvasive method used to help determine the cause and assess the severity of sensory abnormalities.
How does quantitative sensory testing work?
QST uses a vibratory, hot and cold stimulation to determine sensory thresholds. The patient is instructed to inform the examiner when the sensation is initially present. The results are then compared to a series of normal patients as well as from the patient’s own non affected side. The sensory stimuli can varied in much the same way as a hearing test.
Does the test hurt?
No. During the test, the patient feels only mild vibration or hot and cold sensation depending on specific test selected. The vibratory, hot and cold stimulation is limited so that no tissue damage will occur. Unlike traditional electromyography (EMG) and nerve conduction velocities (NCV), no needles are required.
Who should receive this test?
Patients with a sensory disturbances in the arms, legs, or trunk the potential candidates for this test. Abnormal sensations such as pain, numbness, tingling, burning may indicate sensory abnormalities. In many cases, the cause of a sensory disturbance can be determined. This test is also useful to help determine the severity of a particular condition. Patients may also require re-evaluation of symptoms over time to assess response to treatment.
What sort of conditions can be diagnosed by this test?
The following is a partial list of the type of conditions that can be diagnosed with the QST:
1. Radiculopathy – a “pinched” or irritated nerves in the back or neck.
2. Neuropathic pain, reflex sympathetic dystrophy – nerves that have become abnormally sensitized.
3. Carpal tunnel syndrome – compression of the median nerve in the wrist.
4. Peripheral polyneuropathies– damage to the peripheral nervous as a result of conditions such as diabetes, thyroid disease, alcoholism, exposure to toxins.
5. Demyelinating diseases – such as multiple sclerosis, viral demyelinating diseases.
6. Whiplash injuries.
What sort of studies are available that support the use of QST?
There have many studies in the literature supporting the use of QST. Studies at leading research hospitals have been conducted on all the above mentioned conditions. In many cases, QST has been as accurate as traditional nerve conduction studies that employ the placement of needles. In fact, in many cases, the QST is more sensitive than electromyography (EMG) and nerve conduction velocity (NCV).
Does QST replace EMG/NCV?
No. Both tests have advantages and disadvantages. The QST test is better at detecting damage to small nerve fibers such as those that carry information for pain, hot and cold temperature. The EMG/NCV test is indicated in evaluation of weakness. In general, the QST is more sensitive at detecting abnormalities, while the EMG/NCV is more specific. The QST test requires a cooperative patient, while the EMG/NCV test can be performed without patient assistance. The QST is not required the use of needles, while EMG/NCV requires needle puncture.
Does the QST test replace x-rays?
No. The QST tests the function of sensory nerves. Radiological examinations such as plain x-rays, CT scans, and MRI scans are designed to detect anatomical abnormalities. In some cases, the abnormality may be minor or insignificant on a radiological examination but be significant on the QST.
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