Oct 16, 2012

Skin Biopsies for POTS Patients - worth it?

If you want the short answer, yes, I think skin biopsies looking for sensory and sudomotor abnormalities are worth it for some POTS patients.

The long answer...
I'm not a doctor, so you should discuss this with your own physician.  I am a POTS patient who was able to figure out the underlying cause of my POTS because a chance skin biopsy performed on me revealed autonomic neuropathy.  This led me to push my doctors to find the cause of the neuropathy, since I was sure the autonomic nerve damage was causing the POTS symptoms.  We found the underlying cause of my nerve damage (and autoimmune disease, Sjogren's Syndrome), treated it directly with IVIG and now I am doing awesome.  We have used skin biopsies to monitor the progress of my treatment.  We have seen the nerve damage heal over time because we are treating the root cause of the nerve damage, rather that just masking symptoms with the traditional POTS medications.

Why are skin biopsies even relevant to POTS?
Mayo Clinic has two different studies showing that at least 50% of POTS patients have a peripheral autonomic neuropathy.  It does not seem to be a full body widespread autonomic neuropathy in most patients.  One reason we know this is because, on the whole, POTS patients do not have cardiac autonomic neuropathy, which is seen in about 20% of diabetic people who have diabetic autonomic neuropathy.  That is a more serious form of autonomic neuropathy.  Of course, POTS is serious, but the neuropathy involved with typical POTS doesn't appear to impact the heart.  Our tachycardia is not caused by nerve damage to the heart.  It is essentially a healthy tachycardic response to other stresses on our vascular system (low blood volume, increased norepinephrine, venous pooling in the legs and stomach, etc.).

I believe that all patients should try to learn as much about their own manifestation of POTS as possible.  You can then try to tailor your therapies to what you find out.  For example, if you have EDS, you would make sure that you take extra precautions during exercise.  If you have autonomic neuropathy, you would make sure you are not taking any medications that could make this worse (some medicines can cause neuropathy, others can make the symptoms of it worse).  Also, if you have confirmed autonomic neuropathy, it means your doctors should be helping you look for the cause of the nerve damage.  If your doctor won't do that, then you need to find a new doctor.

Not everyone who has autonomic neuropathy will be able to determine the underlying cause of the nerve damage.  However, to me, it is unacceptable for physicians to dismiss nerve damage as "idiopathic," which means "of an unknown cause," until they have done a careful and methodical search for a potential cause of the nerve damage.  In my own experience, and from what I have heard from other POTS patients, physicians rarely look carefully for the cause of autonomic neuropathy in POTS.  Perhaps the patient has had a few simple blood tests checking for common things like diabetes or Lyme Disease, but after than, it seems like many doctors give up and send the patient home with an "idiopathic" diagnosis.  This is not fair to patients.  If a cause can be determined, there is a good chance that the patient will be able to directly treat that cause.  This can help them prevent further nerve damage, stabilize the damage that has already been done, and perhaps prevent future damage.  I am proof that if you treat the autonomic neuropathy directly, you can feel much better.

Additionally, I have heard from many patients who were told they didn't have neuropathy by a neurologist who only did a quick physical exam and an EMG test.  EMG testing cannot detect damage to small fiber nerves.  EMG only tests large fiber nerves.  A normal result on EMG testing does not mean you don't have neuropathy.  it just means you don't have large fiber neuropathy.  We already know that most POTS patients don't have large fiber neuropathy, and that about 50% of them have small fiber autonomic neuropathy.   Similarly, and MRI will not detect small fiber neuropathy.

What do skin biopsies test for?
In the context of POTS, there are two different types of skin biopsies.

The first is called an ENFD (epidermal nerve fiber density).  This is a older form of skin biopsy that is used to look for damage to the small fiber sensory nerves in your skin.  If you have shooting nerve pains in your feet, and sometimes your hands, tingling, burning, pins and needles... you probably have small fiber sensory neuropathy.

The second is called SGNFD (sweat gland nerve fiber density). This is a newer form of skin biopsy that is used to look for damage to the small fiber sudomotor nerves in your skin, that innervate your sweat glands.  These sudomotor nerves are part of the sympathetic nervous system, and they are considered autonomic nerves.  When the SGNFD biopsy is done, they can also look at the small fiber sensory nerves at the same time.  Interestingly, the SGNFD test can reveal sensory nerve damage even if the EPNFD is normal.  It is fairly common to have sensory neuropathy and autonomic neuropathy in the same patient, although sometimes only one type of nerve is impacted.

You can use these tests to see if you have small fiber nerve damage in the first place, and then if you do, you can have follow up biopsies over time, one year, five year, etc. to see if your nerve damage has improved or worsened or stayed the same.

Is this the same thing as a QSART?
No, but the SGNFD does look for something similar.  QSART stands for Quantitative Sudomotor Autonomic Reflex Test.  QSART involves applying a small amount of acetycholine to your skin and then passing a very small electrical current through it, and then recording how well your sweat glands work.  If the QSART is abnormal, you most likely have an autonomic neuropathy, but the QSART does not directly measure your nerve damage.  QSART was invented by Dr. Low at Mayo Clinic before the SGNFD skin biopsy was commercially available.

Where can I get an SGNFD skin biopsy?
Any doctor can order a SGNFD test kit, from anywhere in the world.  That is why the SGNFD test is so great.  You don't have to wait months or years to get into an autonomic specialty clinic.  You can just have your local physician order the test kit from Therpath.  The doctor doesn't even have to be a neurologist.  He or she can very easily perform the skin biopsy.  It is not rocket science.  Then the lab that makes the test kits will send the results and an interpretation back to you and your doctor.

Are skin biopsies reliable?
Yes, studies by reputable autonomic experts have shown that the SGNFD is more sensitive that the QSART for the evaluation of small fiber autonomic neuropathy, as well as small fiber sensory neuropathy.

Do skin biopsies hurt and will they leave a scar?
A little bit, but only a pinch for a second or two.  Your doctor can give you a small injection of Lidocaine or another numbing agent just before taking the biopsy.  The size of the biopsy is only 3mm across by 3 or 4 mm deep.  It only takes a few seconds.  I have had a total of six skin biopsies.  Some with Lidocaine, some without.  Personally, I think the injection of the Lidocaine hurts more than the biopsy itself.  After the sample is taken, your doctor will put some gauze and tape, or a regular bandaid on the biopsy site.  It will form a scab the size of a freckle and heal in a few weeks.  Of my six biopsies, only one has a visible scar, and it really looks like a white freckle.  No one notices it except for me.


  1. If your QSART was negative is it possible that you still have small fiber neuropathy? What would you recommend in that case?

  2. I am not a doctor, so I really can't recommend anything. But, I have read peer reviewed journal articles noting that QSART is not as precise as a SGNFD skin biopsy, ar at least that SGNFD is more likely to pick up neuropathy that QSART might miss. I also know that QSART only checks for sudomotor (a form of autonomic nerve) impairment, and "small fiber neuropathy" also includes sensory nerves. QSART does not check your sensory nerves. A SGNFD can look at your sensory and autonomic small fiber nerves.

    In my own experience, my QSART only had a very mild abnormality but my skin biopsies (done at different hospitals by different doctors) all showed severe small fiber nerve damage.

  3. Cardiac Autonomic Neuropathy Testing is must, Autonomic neuropathy affects the autonomic neurons of either or both of the parasympathetic and sympathetic nervous systems.

  4. In some forms, the degree and type of autonomic system involvement varies extensively, so Cardiac Autonomic Neuropathy Testing is must.