Focal neuropathy is a type of diabetic neuropathy that occurs within one specific nerve or groups of nerves. Because the damage occurs within a specific “local” area, this condition may also be called localized neuropathy. As with more common forms of neuropathy (e.g., peripheral, autonomic), focal neuropathy may affect several parts of the body in some patients.

The nervous system is a complex and delicate system in the body. It is made up of two main divisions, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and the spinal cord. The PNS connects the brain and spinal cord to the rest of the body. These two systems basically control movement and sensation in the body.

Within the peripheral nervous system, the basic units are neurons (nerve cells). These cells have bundles of fibers classified as:

• Motor fibers. These nerves carry messages from the central nervous system to organs and muscles. When the message is received by the body it reacts with an action or movement. Motor neurons are responsible for voluntary movements (those the body can control).
  
  
• Sensory fibers. These nerves carry messages from sensory receptors throughout the body. The messages, or nerve impulses, provide information about physical feelings such as pain and temperature. The messages are sent from the body to the central nervous system in the spinal cord and brain.
  
  
• Autonomic fibers. These nerves are involved with the body’s involuntary functions (things that typically are not consciously controlled, such as breathing, regulation of blood pressure, sweating, digestion and bladder control). The nerves help control these functions whether the individual is awake or asleep.

Focal neuropathy is technically a form of peripheral neuropathy because it involves peripheral nerves. However, it is unlike typical diabetic peripheral neuropathy in that it develops quickly and affects specific nerves.

There are several suspected changes in the nerve that cause diabetic neuropathy. When the nerves are surrounded by a high level of glucose (blood sugar), they adjust their inner workings to be in balance with their surroundings. To create this balance, the nerve cells produce and store the sugar sorbitol. Sorbitol can damage the nerve cells, which results in problems such as pain, numbness or weakness. In addition, the nerves may be damaged when they do not receive enough oxygen from the surrounding blood vessels.

Focal neuropathy can affect motor and sensory nerves. The problems from focal neuropathy vary according to the type of nerves affected:

• Motor nerves help muscles contract. Damage may result in muscle weakness, poor coordination and reduced range of motion.
  
  
• Sensory nerves help with feeling of sensations. Damage may result in tingling, pain or numbness.

A person with diabetes can have sensory and motor damage in one area at the same time. The combination may result in particular difficulties, especially when it involves the feet.

Focal neuropathy also may develop when there is a blockage in the blood vessel that supplies the nerve. Without proper blood flow, the nerve does not receive the necessary oxygen and nutrients to keep it healthy. Damage to blood vessels (angiopathy) can itself be caused by uncontrolled diabetes.

In some cases, focal nerve damage may develop when a nerve is compressed or pinched. This type of damage frequently occurs when the nerve is against a bone or in a tight space on the body. It also may be referred to as an “entrapment syndrome.” Carpal tunnel syndrome is an example of this type of nerve damage (compression neuropathy). Diabetes and pregnancy are risk factors for this painful syndrome.

Focal neuropathy also may be responsible for vision problems. When the nerves connecting to the eyes no longer receive adequate blood supply, the eyes may be unable to function normally. The result of the nerve damage may be blurred or double vision.

The severity and duration of the symptoms from focal neuropathy vary according to the type of nerve damage. By changing the contributing factors, such as adopting a better diet and exercising more, the patient can lessen the symptoms. In general, the symptoms disappear within weeks but may last up to several months if no changes are made by the person with diabetes. The symptoms from focal neuropathy can be very painful but typically do not cause any permanent damage. Reducing the risk factors is the best way to decrease the difficulties from focal neuropathy.

According to the American Diabetes Association (ADA), individuals who have had diabetes for more than 25 years have a 60 to 70 percent chance of developing some form of neuropathy. Although focal neuropathy is not the most common form of diabetic neuropathy, it can be painful and unpredictable. It is important for people with diabetes to seek medical attention if they notice a sudden onset of pain or loss of feeling. A physician can determine the presence of focal neuropathy and provide a diabetic treatment plan to help shorten the duration and severity of the symptoms.