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.

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.

A physician will examine a patient before determining whether or not quantitative sensory testing (QST) is advisable. Generally, patients are good candidates for this test if symptoms are experienced in the arms, legs or trunk and are related to sensory abnormalities. Such symptoms may include:

• Burning
  
• Numbness
  
• Pain
  
• Tingling

There are no special preparations required by the patient before QST. The examination is generally performed at a physician’s office rather than an outpatient center or hospital. Just prior to testing, the patient will be required to remove clothing from the area to be tested. This may be as simple as rolling up the pant legs or shirt sleeves.

QST requires the cooperation of the patient. During the procedure, a physician or other test administrator will use a computer testing system or other standardized sensory testing instruments to administer a series of stimuli to affected and unaffected regions of the body. These stimuli include:

• Heat – about 113 degrees Fahrenheit (45 Celsius)
  
• Warmth – about 86 degrees Fahrenheit (30 Celsius)
  
• Cold – about 50 degrees Fahrenheit (10 Celsius)
  
• Vibration

The patient is asked to report sensations as soon as they occur so that the healthcare provider performing the test can record the information. The sensations are introduced very briefly and usually cause minor, if any, discomfort.

QST relies upon two testing methods. They are:

• Method of limits. Similar to a hearing test, patients are asked to notify the physician as soon as they detect an increasingly strong stimulus, or when they can no longer detect a decreasingly strong stimulus.
  
  
• Method of levels. Stimuli of varying intensity levels are administered, and patients are asked whether or not they felt each individual stimulus.

For both methods, the amount of time stimuli are exposed to the patient is typically very brief. Although the QST procedure is generally painless, patients may experience some discomfort when responses to heat and cold are tested. Unlike other tests (e.g., electromyography and nerve conduction velocity studies), needles or electrical shocks are not used during a QST.

Both sides of the body are examined and tested, and results are compared with those of individuals with no sensory impairment. If just one side of the patient’s body is affected, the affected side will also be compared to the healthy side.

Depending on the patient and the nerves to be tested, the time required to perform the entire QST ranges from 60 to 90 minutes.

Patients are free to resume their normal routine after testing. They will not experience side effects from this procedure. Results are typically available quickly, and may be provided to the patient over the telephone. Patients are urged to consult with their physician to discuss their QST results and treatment options, if necessary.

Preparing questions in advance can help patients to have more meaningful discussions with healthcare professionals regarding their condition or test. Patients may wish to ask their doctor the following questions related to quantitative sensory testing:

1. Would I benefit from receiving quantitative sensory testing (QST)?
   
   
2. Will QST show if I have neuropathy (nerve damage)?
   
   
3. Which other condition can QST help to diagnose?
   
   
4. Will I need additional testing, besides the QST?
   
   
5. When and where will my QST take place? How long will it last? Who will conduct it?
   
   
6. Do I need to do anything to prepare?
   
   
7. What can I expect during the test? Will I experience any pain or discomfort?
   
   
8. When and how will I receive my test results, and who will explain them to me?
   
   
9. What do my test results show?
   
   
10. If treatment is necessary, what are my options?
    
    
11. How often do you recommend I have QST?