Transcription:

UAB Med Cast is an ongoing medical education podcast. The UAB division of continuing education designates that each episode of this enduring material is worth a maximum of .25 AMA PRA category 1 credit. To collect credit please visit www.uabmedicine.org/medcast and complete the episode’s posttest.

Melanie Cole (Host): Today, we are examining the thermoregulatory sweat test and my guest is Dr. Mohammed Kazamel. He’s an Assistant Professor in the Department of Neurology at UAB Medicine. Dr. Kazamel, how might our sweat be one of the earliest manifestations of nervous system disorders?

Mohammed Kazamel, MD (Guest): First of all, thank you Melanie for having me again. So, the sweat function represents an integrated function of the whole nervous system from the central nervous system and specifically the area of the hypothalamus down to the brainstem and then the spinal cord and then the peripheral nerves and then the fine small nerve fibers which are very important in regulating the sweat function of our body. Lack of sweat gives us like an idea about the localization of any problem that happens in the central nervous system including the brain and the spinal cord or the peripheral nervous system including the small and the large nerve fibers.

Host: Then tell us about the thermoregulatory sweat test and how is it an important tool in assessing the entire pathway that controls sweat functions that can help to delineate the diagnosis in a variety of central and peripheral nervous system disorders?

Dr. Kazamel: So, the thermoregulatory sweat test tests the pattern of lack of sweat so what we do in our lab is that we ask patients to come on the morning of the test and they take off most of their clothes and then we dust the whole body with a certain kind of powder called alizarin powder and this powder has a specific quality of changing its color from sandy yellow to deep purple when it gets exposed to water or sweat. What we do after that is that we insert the patient into a closed booth and the temperature and the humidity inside the booth continues to raise slowly to make the patient sweat in a very controlled manner.

Then depending on which areas sweat and which areas do not sweat; we are able to localize where the lesion exactly. For an instance, people who have central neurodegenerative disorders like multiple system atrophy do not sweat at all. While people who have spinal cord lesions, specifically the high spinal cord lesions in the cervical or the upper thoracic spine do not sweat below that level. While people who have peripheral neuropathy, specifically the small fiber neuropathy type, they do not sweat on the most distal parts of their limbs namely the toes. So, this is how our sweat test helps us to localize where the lesion including central and peripheral nervous system disorders.

Host: When would the test be used Dr. Kazamel? What are the diagnostic criteria for administering this test?

Dr. Kazamel: So, we receive referrals for again, central and peripheral autonomic disorders and we receive referrals for people who have problems with number one, lack of sweat plus problems with their cardiac autonomic functions including orthostasis and difficulty of standing upright due to feeling of cerebral hypoperfusion symptoms including dizziness, lightheadedness, headache, tunnel vision, all of that. So, we receive those referrals for those patients having these symptoms, combined symptoms of cardiac autonomic failure and inability to maintain the blood pressure in upright position and also lack of sweat. And we try to evaluate those patients whether they are having a central problem like multiple system atrophy or advanced Parkinson’s disease or a peripheral problem like small fiber neuropathy, specifically diabetic small fiber neuropathy.

Host: What are some of the limitations of this test doctor? Is this a widely adopted protocol?

Dr. Kazamel: It’s not a widely adopted protocol at all. Some of the limitations of this test is it is really not available in every autonomic center in the country. In fact, six or seven autonomic centers in the country currently have this test. Although the test has been known for a long time. The test has historically – has been available in England since the 60s and Mayo Clinic in the 80s brought it into the US. Despite the fact that the test has been known since 80s, or the late 80s to more specific; only seven centers have adopted the test realizing its integrative importance in diagnosing people with – patients with autonomic dysfunction.

Host: Is that because it’s time consuming or requires very specialized equipment, a large clinical space and also speak about limitations in terms of how it can localize specific areas of your sudomotor dysfunction or where it cannot do just that.

Dr. Kazamel: So, first of all, the test is very – it is kind of laborious and it requires like an hour and a half to be conducted. It require preparation from the standpoint of the patient. We ask patients not to take any medications that interfere with their ability to sweat including very common antihistamine over-the-counter medications or allergy medications for an instance. Those have anticholinergic properties and they actually prevent patients from sweating. Also, we require the patient to come to the test in the morning very well hydrated, so they have the ability to sweat profusely if their sweat function is normal. It also, it takes some time to operate the test because some people do not sweat easily so we require them to stay inside the booth for like 50 or sometimes 60 minutes and some patients cannot tolerate that. So, these are the limitations when it comes to the technical aspects of the test.

Having said that, the appropriate preparation of the patient via detailed instructions has helped us here at UAB to avoid multiple of these limitations specifically the medication interference with the results of the test.

Host: Tell us how the results of the test are interpreted and the diagnosis. How is it made and what do those different patterns of sweat or lack of sweat help you to determine? Give us examples of what you might notice.

Dr. Kazamel: So, again, the lack of sweat pattern depends really on where is the lesion in the central or the peripheral nervous system. A patient who has late Parkinson’s disease dementia with Lewy Body or multiple system atrophy will not sweat at all despite appropriate heating and exposure to humidity, even if an hour passes. While patients who have spinal cord problems will not or lesions will not sweat below that level of the spinal cord. We see those cases in patients who have high spinal cord injuries at T6 or mid thoracic level or higher. Also, it happens on ipsilateral contribution, so it tell us also what side of the spinal cord is not functioning. Cases of small - peripheral neuropathy of the small fiber type, these do not sweat on their toes. So, pretty much these are the three localizing categories of – the three common localizing categories of central and peripheral nervous system disorders that we see. Sometimes people have problems with dermatomal lack of sweat distribution due to an active herpes zoster infection. We see those a lot. Some types of diabetic root problems we call them diabetic radiculopathies happen in the abdomen and these are quite painful and gets diagnosed with this test too if the patient is not able to sweat over that particular dermatome distribution on the trunk.

Host: Doctor, before we wrap up, how can this test help to manage and not just diagnose nervous system disorders?

Dr. Kazamel: That’s a very important question. So, we see cases of inflammation and degeneration of the autonomic ganglia called the autoimmune autonomic ganglionopathy. And these cases are very important number one to diagnose and because this is a – in the majority of cases are treatable cases and whenever we treat them with immunomodulatory treatment like IVIG or immunosuppressive treatment like large dose of steroids; this test is helpful in seeing people restoring their autonomic function specifically the sweat functions over time. Over time, what happens in these cases is that the powder starts to change its color over the areas that remained dry before treatment. So, the test is also an important in following up those cases.

Host: Then wrap it up for us, what you would like other providers to know about this test and the fact that it is being done at UAB Medicine and when you think referral if very important.

Dr. Kazamel: So, the thermoregulatory sweat test or the autonomic chamber remains an integrative test that helps us with other autonomic function testing that we have here in the lab to comprehensively evaluate patients with dysautonomia’s. Two categories of referral could benefit from this test. First the central autonomic dysfunction cases including late Parkinson’s disease patients who have typically hypotension and lack of sweat. Also, cases with dementia of Lewy Body and multiple system atrophy. The other category is the peripheral category of cases of small fiber neuropathy. This test and specific is the most sensitive test available with a sensitivity of 92% even more than the skin punch biopsy. So, cases of diabetic small fiber neuropathy or idiopathic small fiber neuropathy will benefit also from this test. So, these are the two categories of referral that I think we are able to help here using that test in our comprehensive UAB autonomic function testing laboratory.

Host: Thank you so much Dr. Kazamel for joining us today and telling us about this highly specialized test for nervous system disorders. Thank you again. A community physician can refer a patient to UAB Medicine by calling the MIST line at 1-800-UAB-MIST. That’s 1-800-822-6478. You’re listening to UAB Med Cast. For more information on resources available at UAB Medicine you can go to www.uabmedicine.org/physician, that’s www.uabmedicine.org/physician. This is Melanie Cole. Thanks so much for tuning in.