Feeling sunburnt in winter? It could be small fiber neuropathy.



Nerves are composed of bundles of individual fibers (axons)


Nerve fibers (axons) come in a variety of shapes and sizes.  Some are wrapped in insulation (myelinated) others are bare (unmyelinated).

Human nerve

You can see from the figure (above) that small unmyelinated fibers make up the majority of human sensory nerves.  These small unmyelinated fibers convey pain and temperature sensitivity.


Small fiber neuropathy

Some diseases, particularly diabetes, preferentially affect these small unmyelinated fibers, leaving the other fibers relatively unaffected, resulting in small fiber neuropathy.

Symptoms of small fiber neuropathy are usually a mixture of numbness (sensory loss) and neuropathic pain.

The pain can be superficial and burning, deep aching, pins-and-needles, electrical shocks, or knife-like stabbing.  Innocuous contact (such as with clothing or bedclothes) can become painful like a sunburn.

Small fiber symptoms often worsen at night (when there are fewer distractions) and in the cold.

The symptoms usually begin in the feet, often first affecting the toes and/or soles.  As the condition worsens, the symptoms usually spread proximally up on to the legs and ultimately on to the hands, leading to a “glove and stocking” pattern.

Peripheral Neuropathy, Length Dependent

In most neuropathies, the ends of longest nerves are affected first (left), leading to a glove and stocking distribution of pain and numbness (right).


Autonomic dysfunction from small fiber neuropathy can cause burning redness in the feet (“erythromelagia”):



Also, loss of innervation to the sweat glands can cause decreased sweating peripherally (where the neuropathy is worse), and lead to increased sweating on the head and trunk:

sweat test

Sweat test showing decreased sweating in t extremities (yellow) and increased sweating on the head and trunk (purple).


A Diagnostic Challenge!

It is the large myelinated fibers which sub-serve strength and deep tendon reflexes.  Furthermore, it it these same large myelinated fibers which are tested during a conventional nerve conduction study.

So the physical signs and electrophysiologic findings we typically rely on to diagnose neuropathy may be absent in small fiber neuropathy.

The most widely available diagnostic test is the punch skin biopsy to quantify epidermal innervation.

skin biopsy neuropathy

Skin biopsies, showing normal epidermal innervation (left) and epidermal denervation in small fiber neuropathy (right).


Managing Small Fiber Neuropathy

So, you know you have sunburn from small fiber neuropathy, now what?

The most important first step is to look for an underlying (treatable) cause, particularly occult diabetes, with blood work that includes a glucose tolerance test.  In the case of diabetes, monitoring and controlling the blood glucose, is the most important next step.

Otherwise, treatment is usually limited to symptomatic measures, using drugs like gabapentin, pregabalin and/or duloxetine.


5 thoughts on “Feeling sunburnt in winter? It could be small fiber neuropathy.

  1. I have small fiber neuropathy which developed spontaneously on August 2013.
    My left big toe started tingling and this tingling started to go up my leg.
    In December 2013 the same started in the right leg, beginning at the right big toe.
    A few weeks later I had a circulatory collapse and got in hospital but everything seemed okay.

    In April 2014 a doctor tested my urine on Thallium (TI) and the level was 3.0 microgram per liter (Shouldn’t be over 0.7). They tested it 5 times but the level was always over the limit.
    I just can imagine how high the level was between December ’13 and April ’14.

    Nobody knows if the SFN is caused by the Thallium intoxication.
    Nobody else of my family got any symptoms of an intoxication.
    The only difference was that I got braces on January 2012.

    2 weeks after a got the braces I started sweating more than usual.
    At this time I couldn’t sleep very well and got hairloss but everything else seemed to be alright.

    In February 2014 the braces were removed and I got a second circulatory collapse.
    I swallowed some of the dust when the doctor removed the glue off my teeth.

    I’ve taken a few of the ceramic- and metal brackets and analyzed it.
    The brackets didn’t contain any Thallium. Only a bit of Boric (B), that’s all.

    So far my Thallium level in my urine is under the limit (0,28).
    But I still got this SFN which gets worse.
    It already got from the toes up to my face.
    It’s really like sunburn with hypersensitivity.

    I checked the Vitamin levels, got OGTT, globulin levels, SCN9A & 10-GEN, Fabry disease, amyloidosis, cryoglobulins, some hormons…the only thing which does not seems alright is TSH level. It jumps up and down. The other thyroid results were okay.
    No hasiomoto and no Graves’ disease. The docs say it isn’t caused by the thyroid.

    I can only say that my symptoms get worse when I eat or drink something.
    After 4-5 minutes I get tinnitus and the tingling gets worse…
    I checked some enzymes – were okay.

    Now it’s already 2015 and I’m feeling still like crap and didn’t find the cause.

    I’ve read some articles from Araim Pharmaceutialcs which is testing a product called ARA 290. ARA 290 shall activate the body’s natural repair receptor which should repair the damaged nerve fibers. But this will take a while until anybody can buy this…

    I’ve already tested some medicals.
    But none of them made the symptoms disappear…

    It’s really a shame that the human body is so fragile.

  2. May be calling for an appointment. Have small fiber neuropathywhich developed spontaneously as “glove and stocking:” syndrome two years ago without any usual factors.Am healthy weight and nutrition good. Sugar numbers, etc, fine and other conditions like MS ruled out.. Told by one neurologist my hypothyroidism could be a cause?. I am beginning to wonder if statin use could relate to and considering discontinuing for awhile to see if symptoms improve..Concerned it will progress without dx.

    • Thanks for your comment Mary Jo. I would be happy to see you, and try to find out more about your neuropathy. Impaired glucose metabolism is by far the commonest cause of painful neuropathy, and can be hard to pick up, particularly early on. Did you have a glucose tolerance test? Hypothyroidism can certainly cause neuropathy. While there is data that shows some epidemiological association between statin use and the presence of neuropathy, I personally remain unconvinced that these drugs actually cause neuropathy, click here to find out more.

      • Thank you for your quick reply.I have not had a glucose tolerance test because neither my internist or the other neurologist I saw felt there was any issue there with blood work that was done and I was loathe to give up all that time to do it,in all honesty.I am 63 in good shape and health otherwise but have had endocrine issues for decades now – primary ovarian failure at 37 that was likely masked by birth control and probably occurred earlier,hypothyroidism a couple years later that has never felt completely treated and increasingly debilitating fatigue and narcoleptic symptoms prior to this occurrence of neuropathy.That is why the docs felt it was more related to these things.
        The neuropathy is not yet painful -more that feeling of having gloves and socks on, tingling;itchiness and the “sunburn” sensation in toes and lower feet at night.More concerned about its progression.I guess I didn’t want to get caught in the “testing trap” since there is so little that can be done about neuropathy so I live with it. However, a client of mine was singing your praises so I found this site.Perhaps I should do the glucose tolerance prior to setting up an appointment with you so we have a baseline?Are there any other screens you would recommend to do prior? As we all are, I am a busy professional with a practice of my own so better to have as much info for you before an appointment?

      • OK, I would suggest a TSH, vitamin B12, SPEP-IFE and 2hr 75g OGTT, feel free to call my office for a script prior to an appointment. Have a great weekend.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s