The only way to definitively diagnosis small fiber neuropathy is through a skin biopsy.
Small fiber neuropathy results from damage to the small, unmyelinated nerve fibers that convey pain and temperature sensations. Routine neurological exams such as EMG and nerve conduction studies can often be normal in patients with isolated small fiber neuropathy. The physician performs a skin biopsy to more accurately diagnosis a problem with the small nerve fibers. A skin biopsy followed by epidermal nerve fiber density testing can be the only way to make a diagnosis of small fiber neuropathy.
The biopsy can take 15 to 30 minutes depending upon how many sites are biopsied. This procedure is minimally invasive. We routinely do skin biopsy on 1 side at 3 sites, above the ankle (distal leg), above knee (distal thigh) and below hip (proximal thigh) using a 3 mm (diameter) punch biopsy. Since the biopsy size is so small, no stitches are needed. The biopsy sites will be healed within 1 week, but may leave a small scar.