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← Return to biopsy for small nerve fiber
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After my neuro did the usual 1st steps in diagnosing any neuropathies NCT & EMG, he ordered a skin/nerve punch biopsy which is now routinely preformed at the lateral ankle, above the knee and upper thigh. When these three areas show decreased fiber density they compare the nerve fiber densities/mm to the normal readings and it will indicate whether one has the more common length dependant SFN (usually caused by diabetes, metabolic conditions, vitiman deficiencies, etc), or the more rare non lenght- dependant SFN which is more ofter caused by autoimmune diseases or other non-metabolic causes. This gives them a very good idea where to begin in looking for the cause and stopping the progression from small fiber to affecting large nerves.
In most cases, unless idiopathic, it is most important to find the cause in order to manage and treat that disease process more than simply treating treating the pain of the SFN as it will continue to progress most often without the cause being managed.
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I understand, but my experience was different. I had four neurologists tell me that at least 30% of skin punch biopsies are negative…despite patients still having symptoms. Maybe that’s the same percentage with idiopathic SFN, which is a huge number. My main neurologist told me this is why someone would say, “It won’t necessarily change the treatment.”
It’s important to find a cause, if one is findable, and the skin punch biopsy can help point to a cause, but in a lot of cases it does not. And even if one does find a cause, the treatment may be the same, i.e. it’s common with fibromyalgia but there’s no direct treatment for fibromyalgia, just symptoms management.
Mine was inconclusive (one sample was “low normal” and the others were not a good sample; I can’t remember exactly, but it wasn’t worth doing again), I have no history of diabetes, a normal glucose tolerance test, no exposure to a chemical, nor B12 deficiency, chemotherapy, never took any medications regularly until that point, etc. It was obvious it was length-dependent because in the time I waited for an appointment, the symptoms began in my feet and crept up higher. All of that was apparent before the skin punch biopsy.
I still decided to do it because I wanted certainty about whether I did or did not have small fiber neuropathy and not some other more resolvable condition. Sadly it didn’t give me that.
My small fiber neuropathy is assumed to be autoimmune because I have an assumed diagnosis of a seronegative inflammatory arthritis (no objective biomarker and joint damage would may not be apparent for decades without treatment despite severe pain) and an objective diagnosis of POTS, which affects the autonomic nervous system—which also relies on small fiber nerves. Treating the inflammatory arthritis improved the joint pain, but not the SFN. IVIG would be my “hail Mary” pass but it’s a toss-up.