Abnormal EMG, Showing Small Fiber Neruopathy? I'm Confused!

[JoshuaY46013]

I've read everywhere that an EMG can NOT pick up Small Fiber Neuropathy, I had an EMG and it picked up NO response in my Plantar Nerves on both feet and my Doctor said that it indicated Small Fiber Neuropathy.

So is it OR isn't it possible? Is my doctor wrong??

I'm SO confused, I have burning all up my shins, why didn't that show up with no response?

[JoshuaY46013]

Thank you so much for the answer to the question.

My doctor told me BECAUSE I had no Medial Plantar Nerve response that it INDICATED Small Fiber Neuropathy.  I'm sure that I have Small Fiber as the burning is unbearable and I can't stand temp. extremes and there is horrible pain BUT the fact that there is NO Medial Plantar Nerve response indicates Large Fiber Involvement?  We've had several discussions over this topic and the answers are always the same, that it is Small Fiber Neuropathy.

I'm a bit confused as to where to go from here.  I don't want to tell my doctor he's wrong, but I'm not sure what measures to take, anymore help would be greatly appreciated!

Thank you SO much
Joshua Young

[Neuro Forum]

Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.

Without the ability to examine you and obtain a history, and review your EMG results, I can not tell you what the exact cause of your symptoms is or what the implications of your EMG findings are. However I will try to provide you with some useful information.

There are 2 types of nerves in our body, large and small. The small nerve endings supply the skin and sweat glands. There are two types of sensory neuropathy: small fiber and large fiber (depending on the size of the nerves affected). With small fiber neuropathies, symptoms including burning or buzzing or other vague symptoms starting in the feet and hands then in some cases spreading to other parts of the body. Small fiber neuropathy is by definition a disorder that is not involving the large nerve fibers to the extremities. Therefore, on examination there is preservation of large fiber sensory modalities, such as vibration perception and perception of limb/digit in space (what is termed proprioception).

Other things that define small fiber neuropathy are normal nerve conduction studies (EMG is the part done with the needle inserted into muscles, nerve conduction (NCS) is the part where the nerve is shocked and responses are recorded), and while nerve biopsy is very rarely done for neuropathies, in small fiber neuropathy, the nerve biopsy would be entirely normal. There is one caveat though, that some parameters on the NCS such as the sural response can be abnormal as people age, so that an abnormal NCS may not necessarily imply a large fiber neuropathy IF there are only specific nerves affected.

I will assume that by planar nerves you mean median plantar nerve response. Again, by definition, small fiber neuropathy is a disorder that shows no abnormalities on nerve conduction studies, including a normal medial plantar response. Therefore, if there is an abnormal medial plantar response, the disorder involves the large fibers. However, with age, some parameters of the NCS can be abnormal, and may not necessarily indicate large fiber neuropathy. A definitive diagnosis of small fiber neuropathy can be made with a skin biopsy so that the number of nerve endings can literally be counted. There are other tests of the function of small nerves that can be ordered, such as QSART testing which looks at how much sweat the skin makes in response to a specific chemical, since sweating is in a sense of function of these small nerves. There are several causes of small fiber neuropathy, including diabetes, vitamin deficiencies, autoimmune problems. In over a third of patients, no cause is identified.

Discussion of your questions with your neurologist is recommended, to help you better understand the implications of your EMG/NCS findings, and what your diagnosis is.

Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck