Quantitative Sudomotor Axon Reflex Test (QSART) is a test to evaluate the integrity of the postganglionic sudomotor system along the axon reflex to define the distribution of sweat loss.
It evaluates the integrity of the postganglionic sympathetic axons.
The bio-impedance electrical stimulation of the skin activates receptors on the eccrine sweat gland.
The sweat response is recorded from four sites: forearm and 3 lower extremity sites and assessed for deficits.
The QSART measures the autonomic nerves that control sweating.
QSART is useful in assessing autonomic nervous system disorders, peripheral neuropathies and some types of pain disorders.
The skin is mildly electrically stimulated,
allowing stimulation of sweat glands.
The QSART measures the volume of sweat produced by this stimulation.
QSART is used to diagnose disturbances of the autonomic nervous system, which controls the sweat glands, heart, digestive system, other organs, and blood pressure.
Useful to evaluate small fiber neuropathy when nerve conduction test results are normal, complex pain disorders,
diabetic neuropathies, enzyme disorders
RSD (Reflex Sympathetic Dystrophy, Complex Regional Pain Syndrome),
Dysautonomia, Pharmaceutical agent
cosmetics testing, dermatological studies, and Multiple System Atrophy (Shy-Drager syndrome).
Baseline sweat production and the
electrical stimuli response represent functions of postganglionic sympathetic sudomotor neurons.
The test is used to assess impaired sudomotor function clinically in thin fiber neuropathy.
It is a sensitive, reproducible, and quantitative method to test sudomotor function.
The axon terminal of the sweat gland under the plate electrode is activated by bio-electrical stimulation; the impulse travel centripetally to a branch point and then distally to the axon terminal and a sweating response results.
Only the postganglionic sympathetic sudomotor axon is involved in this setup.
A latency of 1 to 2 min after the induction of the stimulus: sweat output increases rapidly while stimulation continues.
When the stimulator is turned off, the sweat output returns to its prestimulus baseline within 3 min.
The total amount of sweat output expressed in microliter per square centimeter, and the normal value varies depending on the site of testing, gender, and age of the subject: distal limbs, male, and younger subjects tend to sweat more.
Reduced or absent response indicates postganglionic disorder.
Excessive and persistent sweating is also considered abnormal.
Comparison is made between the two limbs, and the finding of asymmetry of more than 25% is considered to be abnormal.