Evaluation of sudomotor function
Why evaluate sudomotor function?
Sweat glands are innervated by small diameter sympathetic C-fibers. Sudomotor (sweat) dysfunction can be one of the earliest detectable neurophysiologic abnormalities in distal small fiber neuropathies. Quantitative assessment of sweat response has been proposed as an index of the severity and distribution of autonomic failure as well as an early indicator for regeneration of small fibers [1] [2] [3].
Diabetes is shown to be the primary cause of small fiber neuropathy. The ADA has identified sudomotor (sweat) dysfunction as one of the major clinical manifestations of diabetic autonomic neuropathy. Furthermore, the assessment of autonomic dysfunction may identify patients at high risk for cardiac autonomic neuropathy, which carries a very high rate of morbidity and mortality [4].
Peripheral Autonomic Neuropathy and its effect on sweat glands [5]
Need for an alternate measure
The use of skin biopsy to measure Intraepidermal Nerve Fiber Density (IENFD) or sweat gland nerve fiber density (SGNFD) is an accepted diagnostic and surrogate measure of small fiber neuropathy. While skin biopsy is generally well tolerated by patients and accepted by the medical community, it has certain limitations as: invasiveness, risk of infection, bleeding, and a limited number of labs that can process the sample [6].
[1] Illigens et al.Sweat testing to evaluate autonomic function. Clin Auton. Res. 2009:19;79-87[2] Low PA.Evaluation of sudomotor function. Clinical Neurophysiology. 2004:115;1506-1513
[3] Gibbons et al.Capsaicin induces degeneration of cutaneous autonomic nerve fibers. Ann Neurol. 2010:68;888-898
[4] Tesfaye et al.Diabetic neuropathies: update on definitions, diagnostic criteria, estimation of severity, and treatments.
Diabetes Care. 2010:33;2285-2293
[5] Lauria et al.Skin biopsy: a new tool for diagnosing peripheral neuropathy. BMG. 2007:334;1159-1162
[6] Joint Task Force of the EFNS and the PNS.European Federation of Neurological Societies/Peripheral Nerve Society Guideline on
the use of skin biopsy in the diagnosis of small fiber neuropathy. Report of a joint task force of the European Federation of
Neurological Societies and the Peripheral Nerve Society. J Peripher Nerv Syst 2010;15:79–92
Impeto technology principle
The below video describes the principle:
Impeto patented technology measures the capacity of the sweat glands to release chloride ions in response to an electrochemical stimulus. It is a dynamic test equivalent to a stress test.
A low voltage potential of variable amplitude is applied to sensors on regions of the skin with a high density of sweat glands (hands and feet) to extract chloride from the sweat and produce a current.
At a low voltage, the stratum corneum acts as a capacitor and only the sweat ducts allow the transmission of ions from the skin. This ensures that measurements correspond to the local sweat function.
The technology provides a quantitative measure of chloride sweat conductance (measured in microsiemens) and its results serve as a biomarker to assess sweat gland function in relation to sweat gland innervation.
Detection of small nerve fiber neuropathies
The peripheral autonomic neuropathy is a major complication of diabetes.
The sweat glands are innervated by sympathetic unmyelinated nerve fibers of small diameter. Exploring the sweat function was proposed to evaluate the severity of autonomic neuropathy. [1] Neuropathic involvement of small fibers develops very early in patients with diabetes [2].
We find these impairments in other pathologies such as:
The Impeto technology allows to evaluate small fiber neuropathy by studying the sweat function.
Symptoms of peripheral autonomic neuropathies
The table below shows some symptoms associated with peripheral autonomic neuropathies:
[1] Low PA. Evaluation of sudomotor function. Clin Neurophysiol 2004;115:1506-13.[2] Tesfaye S, Chaturvedi N, Eaton SE, et al; EURODIAB Prospective Complications Study Group. Vascular risk factors and diabetic neuropathy. N Engl J Med 2005;352:341-50.
