Peripheral neuropathy is nerve damage that affects the peripheral nervous system (PNS). It can cause symptoms such as pain, loss of sensation or inability to control muscles. In practical usage, the term “peripheral neuropathy” is used interchangeably with the term “neuropathy,” which indicates any type of nerve damage. Peripheral neuropathy is very common. As many as 20 million Americans have neuropathy, according to The Neuropathy Association.

The nervous system controls virtually all activity in the body, including breathing, thinking and movement. It is divided into two parts. The brain and spinal cord make up the central nervous system (CNS), which processes information from the senses and responds with commands to the muscles and glands in the body. The second part of the nervous system is called the peripheral nervous system. The PNS includes the autonomic nervous system (ANS), which is not under a person’s conscious control.

The nerves of the PNS are divided into three categories:

• Autonomic nerves. Regulates activities in the body that are not under a person’s conscious control. Examples include breathing, digesting food, and functions of the heart and glands.
  
  
• Motor nerves. Transmits information from the brain and spinal cord to the rest of the body. These nerves control movements of all muscles under conscious control. This includes grasping things, talking and walking.
  
  
• Sensory nerves. Transmits information about sensory experiences such as the sensation of feeling someone’s touch or the pain that results from a cut.

The nerves of the PNS relay information from the brain and spinal cord (the CNS) to various points in the body. In addition, the PNS relays information from the body back to the CNS. For example, the PNS may send sensory information back to the CNS indicating that a person’s feet are cold, which would then trigger a response from the CNS to take steps to warm the feet. Damage to PNS nerves can short-circuit these messages, preventing them from being sent at all or causing them to be sent at the wrong time or too slowly.

Peripheral neuropathy may occur as a result of damage to a single nerve (mononeuropathy) but is more likely to include multiple nerves (polyneuropathy). In some cases, two or more isolated nerves in separate areas of the body may be affected (mononeuritis multiplex).

Peripheral neuropathy causes various levels of discomfort depending on which nerves are affected and the extent of damage to the nerves. The most common symptoms of peripheral neuropathy are weakness, numbness, tingling and pain, which can be mild to severe. Because motor and sensory axons run in the same nerve bundle, damage to a specific nerve bundle typically affects both motor and sensory functions.

Neuropathies are rarely life-threatening unless other diseases are complicating factors.