What is Quantitative Sudomotor Axon Reflex Test?

Quantitative Sudomotor Axon Reflex Test (QSART) is a diagnostic test for autonomic dysfunction. This is a condition affecting the autonomic nervous system, which regulates vital functions such as cardiac, respiratory, and also the gastrointestinal tract system. Diseases that affect this part of the nervous system also tend to affect the sudomotor function in the extremities, which is a part of the autonomic nervous system functionality. Sudomotor function is the function of the sweat glands.

Indications for performing Quantitative Sudomotor Axon Reflex Test include:

• Acute neuropathies (less than 4 weeks duration): Panautonomic, paraneoplastic, cholinergic, and adrenergic neuropathy, botulism, porphyria, Guillain Barre syndrome, and drug or toxin induced neuropathies
• Chronic neuropathies (more than 8 weeks duration): Amyloidosis, diabetic polyneuropathy, idiopathic panautonomic neuropathy, pure autonomic failure, pure adrenergic neuropathy, paraneoplastic neuropathy, Eaton Lambert syndrome, chronic idiopathic anhidrosis, Sjogren’s syndrome, distal small fiber neuropathy, hereditary sensory and autonomic neuropathies, dysautonomia of old age
• Orthostatic intolerance: Postural orthostatic tachycardia syndrome, mild orthostatic intolerance, and syncope

How is Quantitative Sudomotor Axon Reflex Test procedure performed?

• The skin is wiped clean with alcohol
• Four electrodes are placed over three areas of the leg and one on the wrist
• Acetylcholine, a 10% sodium chloride solution, is infused into the skin through a process called iontophoresis
• The axon, a nearby sweat glands’ nerve terminal, is then activated
• The impulse then travels to the axon terminal of another gland, and acetylcholine is released
• This binds to a receptor on the sweat gland and sweat is released
• This process is repeated at different locations in the extremities, and the quantity of sweat released is measured
• The patient cannot eat, consume caffeine, or smoke for 4 hours before the procedure. Also, it is recommended not to consume alcohol 12-14 hours prior to QSART
• Medications, such as aspirin, over-the-counter cough or cold medications, antihistamines, and antidepressants, should be avoided 48 hours before the procedure
• The entire QSART procedure takes about 45-60 mins

The sweat measurements at different locations help determine the presence of an autonomic nervous system disorder. This test is noninvasive with minimal discomfort to the patient. It has great value in the diagnosis of conditions that cannot be detected by other forms of testing.