WHAT IS SWEAT GLAND NERVE FIBER DENSITY TEST (SGNFD)?
Small diameter nerve fibre (SDNF) neuropathy is characterized by damage to the small nerve fibres located in the internal organs, skin, and nerves of the periphery of the body. When the unmyelinated and thin-myelinated small autonomic nerve fibres are damaged, the symptoms that result can include irregularities in body temperature and sweating, orthostatic hypotension, tachycardia, bowel and bladder problems including constipation, diarrhea, difficulty urinating, sexual hypo- or hypersensitivity, and cutaneous symptoms including hair loss, skin dryness, and brittle nails. Routine evaluation for neuropathy includes electromyelogram (EMG) testing; however, this type of testing only measures large nerves. When an EMG test is negative, a deep tissue biopsy can be used to count the number of small fibre nerves to measure the density of autonomic nerves, which are small-fibre nerve tissue. This test may be used in conjunction with the epidermal nerve fibre density test, which measures small nerve fibre density of sensory nerve fibres, which can also be affected in small fibre neuropathy.