Also called: QST
Quantitative sensory testing (QST) is an examination used to help detect damage to small and large nerve endings in the body. A number of disorders that cause nerve damage (neuropathies) may be diagnosed with QST, such as:
- Peripheral neuropathy. Damage to the peripheral nerves, often those that serve the legs.
- Proximal neuropathy. Nerve damage that primarily affects the hips, thighs and buttocks.
- Carpal tunnel syndrome. A condition that affects the median nerve of the wrist.
- Demyelinating diseases. Disorders that involve a loss of myelin, the sheath composed of white matter that protects and insulates nerve endings. An example is multiple sclerosis.
- Radiculopathy. A form of focal neuropathy characterized by irritated nerves, such as pinched nerves in the back or neck.
- Complex regional pain syndrome. A condition in which the nerves are abnormally sensitive.
In addition to diagnosing different types of neuropathy, QST may be used to monitor the state of a patient’s previously diagnosed neuropathy in order to determine the patient’s response to treatment.
QST consists of delivering a series of hot, cold and vibrating impulses to affected and unaffected regions of the body. The impulses are administered at specific intensity levels to test a patient’s sensory threshold (the minimum and maximum point at which an individual can feel the stimulus). A physician conducts the assessment using standardized sensory testing instruments.
QST generally takes place in a physician’s office. It is a noninvasive procedure, meaning that it does not involve inserting needles or electric probes into the body. QST requires no special pretesting preparations by the patient, and side effects after testing do not normally occur. The patient typically requires a consultation with the physician to discuss any unfavorable results of QST and to examine possible treatment options. QST is generally performed in conjunction with other neurological tests (e.g., nerve conduction velocity studies), and it may not be the sole criteria for diagnosing neuropathy and other neurologic conditions.
About quantitative sensory testing
Quantitative sensory testing (QST) is a medical examination used to help detect damage to small nerve endings and large nerve endings in the body. In this procedure, a computer measures the response of small nerves to changes in temperature and the reaction of large nerves to vibration. The goal is to determine the smallest vibration and temperature change that a patient can feel. The test can reveal signs of nerve irritation and a loss of sensation.
In addition to diagnosing different types of neuropathy, QST may be used to monitor previously diagnosed neuropathy in order to determine how patients are responding to treatment.
The human body is composed of three types of nerve fibers, all of which transmit stimuli to the brain in the form of sensations. They are:
- A-beta fibers. Large nerve fibers that transmit vibratory sensations.
- A-delta fibers. Medium-size nerve fibers that transmit sensations of cold.
- C-fibers. Small nerve fibers that transmit heat sensations.
QST is especially effective because, unlike many other types of examinations, it is able to provide useful information about sensory loss in all nerve fibers, even the small “C” fibers. Nerve dysfunction in both the peripheral and central nervous system can be revealed using QST.
Sensory loss can be divided into four categories, each of which is measured by QST:
- Analgesia. Total insensitivity to painful stimuli.
- Hypalgesia. Diminished sensitivity to painful stimuli.
- Anesthesia. The complete inability to perceive vibration, touch, temperature or pain.
- Hypesthesia. The decreased ability to perceive vibration, touch, temperature or pain.
QST consists of a series of hot, cold and vibrating stimulations to affected and unaffected regions of the body. The stimuli are administered at predetermined intensities to test a patient’s sensory thresholds (the minimum and maximum points at which an individual can perceive a stimulus).
Although QST is relatively painless, the patient may experience slight discomfort when responses to heat and cold are measured. A physician conducts QST using standardized sensory testing instruments.
QST is not the only diagnostic tool used to identify or confirm neuropathy and other neurologic conditions. Physicians may also recommend electromyography (EMG) and nerve conduction velocity (NCV) studies, a pair of tests that are usually performed together. An EMG allows a physician to screen for slow or weak muscle reflexes. An NCV allows a physician to screen for slow or weak nerve impulses. A nerve biopsy may also be recommended for some patients.
QST is an effective method of identifying nerve abnormalities. It is considered to be more sensitive than EMG and NCV tests when detecting damage to small nerve fibers that carry information about pain and temperature sensations. However, EMG and NCV may be more effective in detecting nerve weakness. QST requires active patient cooperation, whereas the EMG and NCV do not. On the other hand, EMG and NCV are more invasive and require the use of needles and electrical shocks, which QST does not.
QST is used in the detection of several types of neurological conditions, including:
- Peripheral neuropathy. Disease that damages the peripheral nerves that relay information between the central nervous system (brain and spinal cord) and other parts of the body.
- Proximal neuropathy. Nerve damage that primarily affects the hips, thighs and buttocks. This condition is also known as lumbosacral plexus neuropathy.
- Carpal tunnel syndrome. A condition marked by the compression of the median nerve of the wrist.
- Complex regional pain syndrome (CRPS). A condition in which the nerves are abnormally sensitive. It may appear as persistent pain of an extremity that gets worse over time instead of better. It is unclear what causes CRPS, although this condition may occur after high-velocity impact injuries, such as those from shrapnel or bullets. The pain is often considered out of proportion to the severity of injury. There are two types of CRPS, I and II, formerly known as reflex sympathetic dystrophy and causalgia.
- Demyelinating diseases. These are disorders that involve a loss of myelin, the sheath made of white matter that insulates the neurons (nerve cells) of the central nervous system. An example is multiple sclerosis.
- Radiculopathy. A condition characterized by irritated or pinched nerves. A type of focal neuropathy, radiculopathy is caused by damage to spinal discs located between the vertebrae. The damage may also be the result of gradual deterioration of a disc’s outer ring, traumatic physical injury or both.