What is Small Fiber Neuropathy?

Small fiber neuropathy — also known as small fiber peripheral neuropathy, C-fiber neuropathy, and small fiber sensory neuropathy (SFSN) — is a type of peripheral neuropathy that affects the small nerve fibers near the surface of the skin. The trademark symptoms of this particular condition are particular sensitivity to heat or cold, though other symptoms consistent with general neuropathy are also often present. A patient suffering from this condition may be troubled by a prickly burning sensation that comes and goes without an obvious cause.

Peripheral neuropathy is the name given to damage to the nervous system as a result of disease or illness in all areas distinct from the brain and spinal cord. It can affect various parts of the body, but most commonly the legs and feet. In addition to small fiber neuropathy, which as its name indicates affects small fiber nerves, there can also be large fiber neuropathy. Small fiber nerves generally conduct only pain and temperature sensations from the surface of the skin, while large fiber nerves are responsible for things like motor functions.

Though a large proportion of peripheral neuropathy cases are considered idiopathic — that is having no single, identifiable cause — small fiber neuropathy does have several prime causes. Diagnosis is not always easy, however, as the condition is considered entirely separate from large fiber neuropathy, which confoundingly often affects some portion of small fiber nerves as well.

A diagnosing physician must determine, therefore, that only small fibers are affected for it to be small fiber neuropathy. This is typically done through an exclusionary process, ruling out all other possible causes first. The most common ultimate cause of proper small fiber neuropathy, when not simply deemed an idiopathic case, is a condition known as Fabry disease. Other causes can include diabetes, human immunodeficiency virus (HIV), and neuralgia, though these are less commonly to blame.

Fabry disease is a rare genetic disorder that if undiagnosed and untreated, can lead to renal damage, heart attacks, and strokes, among other problems. Small fiber neuropathy is one of the main early warning signs of the disease. The relationship between neuropathy and Fabry disease is important, therefore, as a way of heading off the later, more severe results that can occur.

As of 2010, there was no cure for small fiber neuropathy, in part because it is often brought on by Fabry disease. When diagnosed as such, it is treated symptomatically with techniques such as intravenous immunoglobulin (IVIG) and plasmapheresis, which are plasma protein replacement therapies. These are typically done in conjunction with treatments for Fabry disease. When diagnosed as idiopathic, the plasma protein replacement is used along with various antidepressant and anti-epilepsy drugs that have been shown effective at reducing general neuropathic symptoms.