Sudomotor dysfunction is one of the most common and earliest neurophysiological manifestations of small fiber neuropathies.In some instances, the small fibers of the autonomic nervous system can be affected, leading to urinary or bowel problems, episodes of rapid heartbeat (palpitations), dry eyes or mouth, or abnormal sweating. They can also experience a sharp drop in blood pressure upon standing (orthostatic hypotension), which can cause dizziness, blurred vision, or fainting. Small fiber neuropathy is considered a form of peripheral neuropathy because it affects the peripheral nervous system, which connects the brain and spinal cord to muscles and to cells that detect sensations such as touch, smell, and pain. Insensitivity to pain can be particularly problematic. One may be bleeding or have a skin injury without even knowing it. Topographic pattern
Like many polyneuropathies, the symptoms are typically length-dependent, starting in the longer nerves and progressively attacking shorter nerves. This means that symptoms often start in the hands and feet before progressing upwards, and that symptoms are usually more severe in the extremities. Some patients have a widespread, non-length dependent, or "patchy", presentation which is sporadic and can affect many nerves. Patients with Fabry disease have isolated small fiber engagement, and can have a more widespread small fiber disruption. Causes
Mutations in the SCN9A or SCN10A gene can cause small fiber neuropathy. These genes provide instructions for making pieces (the alpha subunits) of sodium channels.
Injury
Sciatic nerve injury occurs between 0.5% and 2.0% of the time during a hip replacement. Sciatic nerve palsy is a complication of total hip arthroplasty with an incidence of 0.2% to 2.8% of the time, or with an incidence of 1.7% to 7.6% following revision. Following the procedure, in rare cases, a screw, broken piece of trochanteric wire, fragment of methyl methacrylate bone cement, or of a Burch-Schneider antiprofusio cage can impinge on the nerve; this can cause sciatic nerve palsy which may resolve after the fragment is removed and the nerve freed. The nerve can be surrounded in oxidized regenerated cellulose to prevent further scarring. Sciatic nerve palsy can also result from severe spinal stenosis following the procedure, which can be addressed by spinal decompression surgery. It is unclear if inversion therapy is able to decompress the sacral vertebrae; it may only work on the lumbar aspects of the sciatic nerves. Sciatic nerve injury may also occur from improperly performed injections into the buttock, and may result in sensory loss. : 66

Other disease
Bernese periacetabular osteotomy resulted in major nerve deficits in the sciatic or femoral nerves in 2.1% of 1760 patients, of whom approximately half experienced complete recovery within a mean of 5.5 months.Sciatic nerve exploration can be done by endoscopy in a minimally invasive procedure to assess lesions of the nerve. Endoscopic treatment for sciatic nerve entrapment has been investigated in deep gluteal syndrome.