Is it small fiber neuropathy or MS?

Question:
I am 63 and have had MS for over 15 years. Recently I was told that my diagnosis is incorrect and that I really have small fiber neuropathy, not MS. I am so confused and need your advice. My symptoms began about 15 years ago with pins and needles sensations and burning in the feet. The symptoms would come and go and get worse in warm weather. Over time the symptoms became constant and then started all over my body. I also experience frequent odd jabbing and shock like sensations. Parts of my body are so painful to touch that having a sheet on me is unbearable. The original diagnosis of MS was made after an MRI scan of my head, but my spinal tap didn't show evidence of MS. I recently had another spinal tap by my new neurologist and it still didn't show any bands. I have been on Copaxone for years and wonder what I should do now?

Answer:
Your symptom description is typical of a small fiber neuropathy. While multiple sclerosis is known to cause odd sensations such as pins and needles, burning and electric shocks, these symptoms are hardly unique to MS and can be seen with any disorder that affects sensory pathways in the nervous system. Most individuals with MS will eventually develop more characteristic symptoms and findings on their exam, especially after 15 years. Since you did not mention any other non sensory symptoms or problems, I will assume that the neurologist who disagreed with the diagnosis of MS did not find any of these abnormalities. It is also not uncommon to misinterpret non specific “white spots” on MRI scans as evidence of MS. The community of MS specialists has developed partially effective descriptors of MRI abnormalities that are more typical of MS, but many neurologists and radiologists remain unaware of these guidelines. The normal spinal fluid results, especially if repeated over time, is important. Very few individuals have CSF negative Multiple Sclerosis after so many years of symptoms.

Small Fiber Neuropathy is a condition selectively affecting the small unmyelinated, peripheral sensory nerves that relay information concerning pain and temperature to your brain. This type of neuropathy has many causes including diabetes and medications (cancer drugs) but a cause is never found in up to half of individuals affected with this disorder. At times people with small fiber neuropathy will have symptoms of autonomic dysfunction including dry eyes and mouth, lightheadedness on standing or spells of syncope, irregular heart beats, problems with sweating, urinary incontinence and erectile dysfunction. 

The diagnosis is made by a careful history and exam usually confirmed by a punch biopsy of the skin to examine the small sensory density of nerve endings under a microscope. Needless to say, the medications used to treat MS are not effective for this condition and should be discontinued. Even if an underlying cause is found, treatment consists primarily of various medications to block or modify the painful sensations. The medications commonly to accomplish this goal include the anticonvulsant class of drugs (gabapentin, pregabalin, carbamezipine, oxcarbezipine, lamotrigine and phenytoin to name a few), topical agents (lidocaine patches and capsaicin) and the tricyclic antidepressant class of medications and more modern alternatives (amitriptyline, venlafaxine and duloxetine). 

Revere (Rip) Kinkle
Director of the UCSD Multiple Sclerosis Center

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