Frequently Asked Questions
Testing sudomotor function can be a fast and accurate method for detecting early stages of neuropathies. Eccrine glands that are responsible for sweat response receive a rich supply of small blood vessels and are innervated by sympathetic C nerve fibers (autonomic nervous system). These fibers are thin and long and so can be impaired at the very early stage of different metabolic diseases. “Sweat response may be the most sensitive test in detecting distal small fiber neuropathy” (Pr Low and Pr Gibbons publications).
SUDOSCAN is a medical device that has been cleared by health authorities in many countries including EC (Europe), FDA (USA) and SFDA (China). The approval process in Japan is ongoing.
SUDOSCAN evaluates sudomotor function on the palm of the hands and sole of the feet where the density of sweat glands is greatest. The underlying technology is based on established principles of the electrochemical reaction between chloride (found in sweat) and nickel (which is a component of the stainless-steel electrodes used in SUDOSCAN). A low DC voltage ≤ 4 volts is applied generating a current relative to chloride (ion) flow supplied by the sweat glands and ducts. An Electrochemical Skin Conductance (ESC) is calculated for each hand and each foot on the basis of the current generated and the voltage supplied. Similar to cardiologic stress tests for which exercise is used as a stimulus to capture specific information that is not assessable in resting state, SUDOSCAN too relies on an electrical stimulus of sweat chloride to capture information about the sweat dysfunction that cannot be diagnosed in usual conditions. For a better understanding see the animation video on the web site. Because the skin’s stratum corneum acts like an electrical capacitor when a low voltage stimulation is applied, the movement of chloride to the electrodes on the surface of the hands and feet can only occur via the sweat ducts, and, we can be certain that we’re targeting the underlying sweat gland and its sympathetic innervations. This underlying theory has been confirmed in a comparative study performed on patients with Cystic Fibrosis (who have high sweat chloride concentration at the surface of the skin, basis of the sweat test) and controls (see publication by Hubert et al).
SUDOSCAN test results are provided as hands and feet conductances (mean of left and right side). High conductances correlate with normal sweat function and healthy nerve innervation (small C-fibers). Low conductances represent peripheral or autonomic neuropathy.
Physicians get simple and immediate information on small autonomic fiber status and use it in various medical settings. Proactive monitoring: Medicine is trending towards prevention of the onset of a disease or complication. Since the long, unmyelinated, sympathetic c-fibers slowly degenerate yet quickly regenerate with changes in a patient’s lifestyle or therapy, physicians can use this information to determine whether or not a patient is “at risk” of developing a complication and take proactive measures with treatment options. Assessing the level of intensive glycemic control for diabetics. It is important to determine whether or not a patient has an autonomic neuropathy before prescribing intensive forms of glycemic treatment. Using this quick screening a physician can decide whether or not he/she must perform more specific but time-consuming tests to assess precisely autonomic function in these patients. Patient drug or lifestyle compliance: SUDOSCAN allows a physician to quickly determine sudomotor functioning as a biomarker for peripheral nerve integrity. Patient compliance can quickly be determined based on how good or how bad their results are. This information is complimentary to traditional blood based testing, but is extremely fast and offers immediate results. No subjectivity is introduced via patient verbal responses and quantitative results allow a precise follow-up.
Anyone can get tested on SUDOSCAN to assess their sudomotor function unless they have a specific contra-indication that would prevent them from performing a scan. As previously described, the potential uses for SUDOSCAN include evaluation of peripheral neuropathy and follow-up for diabetic patients. It can be used in neurology when assessment of small fiber neuropathy especially autonomic is required (amyloidosis, Fabry disease, Parkinson’s Disease).
Small C fiber nerve damage can be observed in subjects with prediabetes or metabolic syndrome. Because SUDOSCAN is non-invasive and takes only 3 minutes to run, you can benefit from knowing your hands and feet conductances – first to establish your baseline levels, then to repeat the test periodically to monitor your numbers. SUDOSCAN allows you to have: Immediate knowledge of sweat gland function as an indicator of peripheral nerve function; Biofeedback: a way to quantify the “status” of your peripheral nerves upon lifestyle changes, e.g. Exercise and its benefits.
Evaluation of sudomotor function using other tests such as Quantitative Sudomotor Axon Reflex Test (QSART) has shown generally lower measures (in sweat output) in women compared with those in men. This can be explained by lower sweat rates in women. Measurements performed by SUDOSCAN don’t depend on sweat rate. A study performed on more than 500 women and more than 200 men showed no significant differences in hands’ and feet’ ESC. This will be confirmed in future pending studies on larger group populations
Studies have been performed in European countries, the USA, India and China in healthy volunteers and in patients with peripheral neuropathy diagnosed by referenced methods. Large databases are available allowing determination of threshold values according to ethnicity. For example healthy African-Americans have lower conductance values when compared to Caucasians. Reference threshold values for specific populations are available on request to allow correct interpretation of results. Larger studies are ongoing to increase our databases.
A large database of healthy Caucasian volunteers demonstrated that SUDOSCAN measured conductance levels do not depend on age. It is in accordance with other methods that demonstrated that small fiber status does not depend on age in healthy volunteers.
Clinical tests run at different temperatures (changes of more than 5°C) demonstrate that temperature variance does not impact test results. Hands and feet have a limited role in thermoregulation due to their small area and thus are less temperature dependent than other parts of the body for their sweat rate. Theoretically, extreme cold temperature on the electrodes could result in vasoconstriction. Large studies will be performed to exactly quantify this effect. Therefore, avoid performing test measurements if the electrodes are too cold or on a patient immediately after coming in from an extremely cold environment. Quick warming by rubbing the hands is sufficient to avoid any disturbance in measurements.
Given sweat rate changes with exercise it was important to evaluate the effects of exercise on SUDOSCAN tests. Measurements were performed before and after high impact exercise on more than 100 subjects. Tests showed a coefficient of variation of 13 % for the hands and of 4% for the feet between these two measurements. These results confirm that SUDOSCAN measurements are not dependent on sweat rate.
Reproducibility is critical for any screening test to be useful. SUDOSCAN has been tested for reproducibility in several clinical studies on large groups of patients with 5% coefficient of variation for feet ESC and 10% for hands ESC, which is excellent in an in-vivo environment. The reproducibility between measurements performed before and after an exercise is also excellent (see above). Analyzing dynamic chloride-ionic flow of the sweat glands (as compared to sweat volume) provides better information since chloride levels do not change with sweat rate (see article by Quinton et al on web site) Also noteworthy is that the reproducibility of SUDOSCAN is significantly better than HbA1c (especially finger stick methods) or the oral glucose tolerance test (both HbA1c and OGTT have an effective reproducibility rate of 20%). [/su_spoiler] [su_spoiler title=”Can children be tested?”] There is no safety concern for testing children on SUDOSCAN. However due to hormonal changes in children, sweat function is not stabilized until 18 years of age. Due to lack of data in this population it is difficult to produce consistent and accurate ESC reference values. Studies in such populations is ongoing. Measures in children under the age of 18 must be interpreted with caution.
Contrary to type 2 diabetes, diagnosis of type 1 can occur before the onset of complications including small C-fiber neuropathies. Thus at the early stages of the disease if the patient treatment is well-balanced sweat function should be normal and conductance values as measured by SUDOSCAN should not be decreased. However with progression of the disease, especially if the patient treatment is not optimal, small C-fiber damage will occur and sweat dysfunction should be evidenced through a decrease in conductances as measured by SUDOSCAN. Due to the absence of a pre-diabetes stage small C-fiber damage in type 1 diabetes can be less and occur at later stages as compared to type 2 diabetes.
HbA1C is used to monitor glycemic levels for the past 3 months period. SUDOSCAN is not a blood-based test but focuses on assessment of the small C nerve fiber damage. As such, SUDOSCAN is a test that can be performed in complement to HbA1c. In addition small fiber neuropathy in type 2 diabetes especially depends not only on hyperglycemia also on other metabolic disturbances such as hyperlipidemia. There is no strict correlation evidenced between HbA1C and Sudocan results. In research studies performed, we’ve observed cases where there were significant decreases in ESC results while no difference measured by HbA1c testing was evidenced.
Nerve conduction studies (NCS, also known as EMG) measure the function of large, myelinated nerves. They can be used for evaluating motor nerves and sensory nerves, but not the sensory nerves that are thin, umyelinated – such as heat, cold, and pain perception. SUDOSCAN specifically measures the function of sympathetic C-fibers on the sweat glands. The function of these nerves correlates closely with small sensory nerves of the C-fiber variety. However SUDOSCAN and nerve conduction studies are not likely to correlate since they measure 2 different categories of nerves. Studies are ongoing in neurology to measure if Sudocan findings could precede EMG abnormalities, especially in chemotherapy induced neurotoxicity.
A length-dependent neuropathy is a pathological disorder in which nerve damage starts at the distal-most part of the nerve and progresses backwards along the nerve (retrograde). This is the most commonly accepted theory on the development and progression of diabetic peripheral neuropathy (DPN). Other neuropathies may attack the myelin sheath, or the neuron body, or cause compression at a distinct spot on the nerve axon. Since SUDOSCAN measures nerve function on the palms and soles, the most distant parts of the body from the spine, it is very accurate at assessing length-dependent neuropathies of the small fibers. A SUDOSCAN test revealing low hand scores may or may not be length-dependent. Some small fiber neuropathies (e.g. some infectious or autoimmune neuropathies) may be more severe in the hands, but also start at the nerve tips and so are length-dependent. Also, in the early development of DPN, there may be a phase of compensatory ‘over-sweating’ in which the feet ESC scores are abnormally elevated while the hand scores may be lower. So a SUDOSCAN with low hand scores and normal feet scores may or may not be a ‘length-dependent’ neuropathy.
Testing intervals should be based on Sudocan results and physician recommendations. If your conductances are within normal limits, testing every 9 to 12 months is typical. Patients with peripheral neuropathies can be tested every 3 to 6 months to follow-up treatment protocols.
Yes. The ability of SUDOSCAN to follow the course of peripheral small fiber and autonomic neuropathy over time is one of its greatest advantages over many other nerve function tests. SUDOSCAN is able to do this for 2 major reasons: – Small nerve fibers, and in particular autonomic fibers, will degenerate and regenerate faster than most other nerves. Therefore a positive or negative response of the neuropathy to a change in therapy or to patient compliance or non-compliance may be demonstrated in as little as 3 months. – SUDOSCAN has a very high reproducibility rate. When a patient has 2 SUDOSCAN tests on the same day, the feet ESC scores will not vary by more than about 5%. So any ESC score change of more than 8 or 10 μS signals a pathological change, not device margin of error.
At the moment physicians have no tool to quickly and easily screen for peripheral small fiber neuropathy, other than the use of skin biopsies that are clearly invasive in nature. Skin biopsies are not performed routinely, especially on diabetic patients with feet lesions. This leaves SUDOSCAN, which has a huge potential to be used by physicians to follow-up patients with Type 2 diabetes as part of the ADA or European guidelines.
Since only direct current is applied during a SUDOSCAN test, it does not interfere with pacemaker electronics; therefore SUDOSCAN should be safe to use in a subject with a pacemaker. To confirm that there is no safety concern tests have be performed to check Electromagnetic Compatibility according to ANSI/AAMI PC69:2007 : Active implantable medical devices— Electromagnetic compatibility— EMC test protocols for implantable cardiac pacemakers and implantable cardioverter guidelines. The conclusion of the tests performed by Laboratoire Centrale des Industries Electriques (LCIE, Fontenay aux Roses, France) is that “SUDOSCAN is compliant according to ANSI/AAMI PC69: 2007 (Annexe M) standard”. (Report October, 2012). However we recommend that patients with pacemakers perform SUDOSCAN testing in the presence of a medical doctor.
Cardioselective beta-blockers should not interfere with SUDOSCAN measurements. However additional testing is needed to confirm this and the potential effect of other cardiovascular drugs.
As SUDOSCAN is based on measurements of sweat glands innervated by cholinergic small C fibers, drugs with high anti-cholinergic effects can influence SUDOSCAN results. Thus tricyclic antidepressant agents (in particular amitriptyline), can significantly decrease ESC measured by SUDOSCAN. It is recommended that patients on such medications omit the drug for a period of 2 ½ half-lives (e.g. 48h) prior to SUDOSCAN testing. If this is not possible results must be interpreted with caution. The effect of medications on ESC measurements is a key point and is under continuous investigation in ongoing studies.
At the moment an observational study performed in an outpatient consult clinic in Germany on two groups of patients with type 2 diabetes, the first one receiving insulin, the second one other anti-diabetic drugs, evidenced that after one year of follow-up patients receiving insulin had an improvement in their conductances while the others had a small decrease. These preliminary results have to be confirmed in a clinical study performed on a larger population.
Small fiber neuropathy has been associated with many medical conditions including glucose dysmetabolism (diabetes or prediabetes). Several recent studies have found a high prevalence of impaired glucose tolerance in patients with peripheral neuropathies with a rate up to 42% in cases initially thought to be idiopathic compared with 14% in the general population (see article on small fiber neuropathy). Furthermore, peripheral neuropathies are not always diagnosed. Depending on the population studied and the diagnostic methods, up to 90% of patients with diabetes have confirmed peripheral neuropathies. Another study showed that patients with metabolic syndrome were twice as likely to present with neuropathy as those without. However there are other causes for polyneuropathies: metabolic syndrome, alcoholism, chemotherapy drug induced neurotoxicity. In all these cases neuropathies are symmetrical as opposed to mononeuropathies which are asymmetrical. If sweat dysfunction is detected by SUDOSCAN, the possibility is high that a lesion of the peripheral autonomic nervous system exists. The cause must be investigated with further clinical assessment and the precise diagnosis confirmed by a more specific (but less sensitive) test, typically glucose based measurements (fasting or post glucose load test i.e. oral glucose tolerance test, OGTT) or HbA1C and lipid profile.
Atopic dermatitis has been shown to increase intraepidermal nerve fiber density (IENFD). This makes sense since many such ailments lead to excessive itching from overly sensitive small nerve fibers. SUDOSCAN measures sympathetic C-fbers, and these nerves tend to be affected in a similar fashion to the small sensory fibers. However, we have not completed studies using SUDOSCAN on patients with atopic dermatitis or any other skin condition and therefore cannot make a statement on how skin conditions affect SUDOSCAN results. Note however, that the skin of the palms and soles MUST be intact – without open sores, ulcers, or lacerations – for SUDOSCAN results to be valid.[/su_spoiler] [su_spoiler title=”How should patients’ hands and feet be cleaned prior to SUDOSCAN testing?”] Palms and soles must be free of dirt, ointments, or lotions prior to testing. Washing with soap and water is always the best option. However, antibacterial hand wipes such as Wet Ones® have been used extensively and do not appear to interfere with SUDOSCAN results. Keep in mind: the palms and soles must be DRY prior to placement on the electrodes; and Surfa Safe – an industrial chemical – is NOT deemed appropriate or safe to clean skin prior to testing.
Not necessarily. Patients with large feet/hands or small feet/hands have been tested, and the patients with larger extremities do not test higher than those with smaller extremities. If, however, the surface area of a hand or foot is severely reduced (e.g. from a previous second or third degree burn or an amputation) with obliteration of the sweat glands, the results will definitely be reduced.