Small fiber neuropathy

Small fiber peripheral neuropathy is a type of peripheral neuropathy that results from damage to the small unmyelinated and myelinated peripheral nerve fibers. These fibers, categorized as C fibers and small Aδ fibers, are present throughout human skin, peripheral nerves, and organs. Small fiber nerves receive somatic afferent signals (somatic afferents) and regulate components of the autonomic nervous system (autonomic efferents). It is estimated that 15–20 million people in the United States have some form of peripheral neuropathy.

Small fiber neuropathy is a condition characterized by severe pain. Symptoms typically begin in the feet or hands but can start in other parts of the body. Some people initially experience a more generalized, whole-body pain. The pain is often described as stabbing or burning, or abnormal skin sensations such as tingling or itchiness. In some individuals, the pain is more severe during times of rest or at night. The signs and symptoms of small fiber neuropathy can occur at any point in life depending on the underlying cause.

Individuals with small fiber neuropathy often cannot feel pain that is concentrated in a very small area, such as the prick of a pin. However, they have an increased sensitivity to pain in general (hyperalgesia) and experience pain from stimulation that typically does not cause pain (allodynia). People affected with this condition may also have a reduced ability to differentiate between hot and cold.

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.

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.