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Sensory-Motor Idiopathic Peripheral Neuropathy
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Sensory-Motor Idiopathic Peripheral Neuropathy

I am a 42 year old female, diagnosised a year ago with sensory-motor idiopathic peripheral neuropathy because the neurologist has not found a cause yet. I just had a second Nerve Conduction Study done. which did show some improvement mainly in the senory nerves. My motor nerve conduction velocities are about the same as the test a year ago on both sides for the peroneal nerve, normal is suppose to be 43msec mine are 33 on both sides, the CMAP for my left side is .63 and right side is .93. Normal is 4.0 or higher. There is still no response for the sensory nerves for my right peroneal, they did get a response for the sensory on my left peroneal on the second study, on the first study there was no response.  Only thing off on the left peroneal for the sensory is the SNAP, it is 8.0 when normal is 15. For the F-wave study 3 nerves had prolonged responses, normal is 55msec or less, Left peroneal is 64.33  the right peroneal was normal at 53.83, right tibial is 59.83 and the left tibial is 60.83. my sural nerve for on the right and left was abnormal on the first study, but showed normal responses on the current study. He has already done a blood workup to look for treatable causes all my labs came back normal. He was thinking an autoimmune problem could be the cause of the neuropathy, but now is leaning toward a possible genetic problem and suggested genetic testing which is not one of my options, because the cost is very expensive. Can hereditary neuropathies have some signs of improvement on conduction studies from one test to the next? The neurologist said some hereditary neuropathies can take up to 10 years to develope. Any imput would be greatly appreciated.  
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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 a doctor.

Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.

Neuropathy can be the result of either small fibers or large fibers or both. In small fiber neuropathy, the EMG/NCS is typically normal. The other type of sensory neuropathy is called a large fiber neuropathy. There are several categories of this type of neuropathy, and there are many many causes. Sensory neuropathies can involve just one nerve or several nerves in the body. The symptoms are sensory loss and if motor nerves are involved, weakness. Some types of sensory neuropathies occur and progress very slowly, others sort of wax and wane (with flare-ups) and some are progressive. One of the most common causes of neuropathy is diabetes, and sometimes only glucose intolerances, or abnormal rises in blood sugar after a glucose load can be the only indication (this is called a oral glucose tolerance test. Other causes include but are not limited to hereditary/genetic causes (such as in a disease called Charcot-Marie-Tooth, in which there is a family history of sensory neuropathy usually from an early age associated with other clinical features such as high-arched feet), autoimmune problems (such as lupus (SLE), Sjogren's, Churg-Strauss (in which asthma also occurs), polyarteritis nodosa, which affects blood vessels), and demyelinating diseases (such as CIDP). Vitamin B12 and B6 deficiency, as well as excess vitamin B6, can also cause neuropathy. Some toxins, such as lead, arsenic, and thalium can cause large fiber sensory neuropathy. Other causes include abnormalities of protein metabolism, as in a type called amyloidosis or monoclonal proteinemia. In many neuropathies, both the sensory and motor nerves (the nerves that supply the muscles) are involved, leading to sensory symptoms as well as weakness.

It sounds like there is much work left to determine the cause of your neuropathy. You should have a thorough autoimmune and endocrinological workup. Also, it may be worthwhile to image your neck, but this may not be necessary depending on the full results of the EMG/NCS. You should continue following up with your neurologist. Many times, neurological diagnoses take time to make.  

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

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