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Quantitative Sudomotor Axon Reflex Test (QSART)
Quantitative Sudomotor Axon Reflex Test (QSART)
| Availability |
Please email the author for information about obtaining the instrument: Dr. Phillip A. Low
The Patent for this test is held by: WR Medical Electronics Co.
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| Classification |
Supplemental: Neuromuscular Diseases (NMD)
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| Short Description of Instrument |
The quantitative sudomotor axon reflex test (QSART) measures the nerves that control sweating. The test involves a mild electrical stimulation on the skin called iontophoresis, which allows acetylcholine, a naturally occurring chemical, to stimulate the sweat glands. The QSART measures the volume of sweat produced by this stimulation. Recordings are typically performed from multiple sites, such as the medial forearm, proximal leg, distal leg and dorsum of the foot.
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| Comments/Special Instructions |
The QSART has been used to help diagnose autonomic nervous system disorders, peripheral neuropathies and some types of pain disorders. The reproducibility of Q-SART responses among subjects, provides a tool to diagnose autonomic postganglionic involvement and to monitor the course of an autonomic neuropathy and its response to treatment. (Low et al., 1983)
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| Scoring and Psychometric Properties |
Scoring: The latency, duration, amplitude of the response are recorded.
Results are analyzed by area under the curve, maximal sweat production and sweat onset latency. (Illigens & Gibbons, 2009)
Psychometric Properties: The QSART has been found to be sensitive and reproducible.
Low et al. (1983) found that the QSART is sensitive and reproducible in healthy controls and in patients with diabetic neuropathy (Low et al., 1986). Tests repeated on two different days show a decrease in sudomotor volume with a high coefficient of regression. In two studies, the coefficient of variation was found to be 8% and 14%. (Low et al., 1983, Low & Opfer Gehrking,1992; Cheshire et al., 2021) The QSART has a sensitivity of 80% and a specificity of > 90%, in the diagnosis of distal small fiber neuropathy. (Low et al., 2006, Stewart et al., 1992)
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| Rationale/Justification |
Strengths: Non-invasive test. High accuracy for the diagnosis of small fiber neuropathy. (Akbar et al., 2023)
Weaknesses: QSART measures the postganglionic sudomotor response and as such is unable to detect preganglionic lesions. QSART is also time-consuming, requires special equipment and is not widely available. (lligens & Gibbons, 2009) Test results can be affected by medications. (Low, 2003)
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| References |
Key References:
Low PA, Caskey PE, Tuck RR, Fealey RD, Dyck PJ. Quantitative sudomotor axon reflex test in normal and neuropathic subjects. Ann Neurol. 1983 Nov;14(5):573-80.
Low PA,. Composite autonomic scores scale for laboratory quantification of generalized autonomic failure. Mayo Clin Proc 1993; 68: 748-752.
Low PA. Laboratory evaluation of autonomic dysfunction, In: Low PA, ed. Clinical autonomic disorders: evaluation and management. 2nd ed. Philadelphia: Lippincott-Raven, 1997: 179-208.
Low PA. Testing the autonomic nervous system. Semin Neurol. 2003 Dec;23(4):407-21.
Additional References:
Akbar M, Wandy A, Soraya GV, Goysal Y, Lotisna M, Basri MI. Sudomotor dysfunction in diabetic peripheral neuropathy (DPN) and its testing modalities: A literature review. Heliyon. 2023 Jul 11;9(7):e18184.
Cheshire WP, Freeman R, Gibbons CH, Cortelli P, Wenning GK, Hilz MJ, Spies JM, Lipp A, Sandroni P, Wada N, Mano A, Ah Kim H, Kimpinski K, Iodice V, Idiáquez J, Thaisetthawatkul P, Coon EA, Low PA, Singer W. Electrodiagnostic assessment of the autonomic nervous system: A consensus statement endorsed by the American Autonomic Society, American Academy of Neurology, and the International Federation of Clinical Neurophysiology. Clin Neurophysiol. 2021 Feb;132(2):666-682.
Cohen J, Low P, Fealey R, et al. Somatic and autonomic function in progressive autonomic failure and multiple systems atrophy. Ann Neurol 1987; 22: 692-699.
lligens BM, Gibbons CH. Sweat testing to evaluate autonomic function. Clin Auton Res. 2009 Apr;19(2):79-87.
Low PA, Zimmerman BR, Dyck PJ. Comparison of distal sympathetic with vagal function in diabetic neuropathy. Muscle Nerve 1986;9(7):592-6.
Low PA, Opfer-Gehrking TL. Differential effects of amitriptyline on sudomotor, cardiovagal, and adrenergic function in human subjects. Muscle Nerve. 1992 Dec;15(12):1340-4.
Low PA. Diabetic autonomic neuropathy. Semin Neurol. 1996 Jun;16(2):143-51.
Thaisetthawatkul P, Fernandes Filho JA, Herrmann DN. Contribution of QSART to the diagnosis of small fiber neuropathy. Muscle Nerve. 2013 Dec;48(6):883-8.
Document last updated October 2024
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