Punch biopsies are usually done on the side of the body where you experience the most symptoms (if you happen to notice a difference, and many people do). You've had the biopsy, so you know the drill, but for others who haven't, I'll elaborate. Between two and four (based on the discretion/preference of the doctor and the recommendations of the lab/kit being utilized) 3mm 'punch' biopsies are taken. Frequently three are taken, distal calf (near the ankle), proximal and distal thigh. These 3mm samples are then (again, depending on the kit/lab) frozen, sectioned into 50 micron thick samples, stained, put under a microscope, and the nerve fibers meticulously counted by a pathologist. The number of small fibers present in the samples are then compared to a reference data set for the specific locations biopsied. Taking three or four samples spanning the length of the leg allow the pathologist to differentiation between length- and non-length dependent SFN. Length-dependent SFN is more common, generally has a slower progression, and symptoms characteristically progress from the feet upwards. Non-length dependent SFN is an indicator that SFN is likely widespread throughout the body, and can cause autonomic nervous system dysfunction; affecting organs and glands along with the skin and muscle symptoms seen in length-dependent SFN. Once you have the diagnosis, there is to my knowledge, little to no significance of having it repeated in your other extremities; you know you have it, and wherever you're feeling symptoms, it's likely SFN is present. Not to mention the biopsy is quite expensive. Repeating the punch biopsies after some time has past from when the first set was taken is a great way for your neurologist to track how the disease is progressing/how well treatment is working. Bakodx and Corinthian Reference Lab's websites, can provide you with more information.

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