Focal Neuropathy – Causes, Signs and symptoms

Focal Neuropathy

Also called: Localized Nerve Damage, Focal Nerve Damage, Localized Nerve Failure, Focal Nerve Failure, Multiplex Neuropathy

Summary

Nerve disease (neuropathy) can be a serious complication of diabetes and other disorders. Diabetic neuropathy occurs most frequently in individuals with a long history of diabetes and poorly controlled glucose (blood sugar). The two most common types of diabetic nerve damage are peripheral neuropathy and autonomic neuropathy. Focal neuropathy is less common and causes different symptoms.

Unlike other neuropathies, focal neuropathy appears suddenly and affects specific nerves. It occurs most often in older people with diabetes. Symptoms are likely to occur in the torso, leg or head. The most common symptoms are pain or numbness, but vision problems also may be present. Although focal neuropathy can be painful and debilitating, it usually improves within months.

As with other neuropathies, the best way to prevent the condition is by reducing the risk factors. Controlling glucose, weight and cholesterol levels helps delay or prevent diabetic neuropathy. Once the neuropathy is evident, a healthy lifestyle (balanced diet, exercise, quitting smoking) can reduce the severity of the symptoms.

A diagnosis of focal neuropathy can be made after a physician reviews the medical history and patient’s symptoms and conducts a physical examination. Diagnostic tests may be conducted to further assess the location and extent of nerve damage.

Treatment focuses on relief of the symptoms caused by the nerve damage. Medications, physical therapy and adaptive equipment can be used to help with pain and weakness. People with diabetes often recover from focal neuropathy with no long-term damage.

About focal neuropathy

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.

Risk factors and potential causes of focal neuropathy

Researchers are not sure of the exact cause of focal neuropathy in people with diabetes. It appears that a long history of diabetes and uncontrolled glucose (blood sugar) is closely associated with the development of neuropathy, although neuropathy has also been found in people recently diagnosed with pre-diabetes. In general, high blood glucose (hyperglycemia) may have a chemical reaction with the nerves or cells around the nerves. This reaction results in chronic nerve damage causing poor transmission of signals between body parts or systems and the brain.

Nerve damage in people with diabetes is likely to be caused by a combination of factors including:

  • Metabolic factors, such as high glucose or abnormal levels of insulin or blood fats (lipids) such as cholesterol

  • Neuromuscular factors leading to damage to the blood vessels

  • Autoimmune factors that cause inflammation in the nerves

  • Mechanical injury such as compressed nerves

  • Inherited traits that increase risk of developing neuropathy

  • Lifestyle factors such as smoking and use of alcohol

The causes are different for certain types of focal neuropathy. For example, mechanical injury is the cause of compression neuropathy found with carpal tunnel syndrome. With this type of nerve damage, the median nerve in the wrist is pinched, causing numbness, tingling or pain in the hand. Compression neuropathy may also cause pain on the shin or foot.

Neuromuscular factors may contribute to focal nerve damage and cause problems with motor weakness in the face or pain in the chest. With a neuromuscular cause, the damage occurs due to inadequate supply of oxygen and nutrients to the nerve.

In general, there does not appear to be a single cause for focal neuropathy. Some of the causes cannot be controlled, such as inherited traits. Other factors, such as glucose levels and lifestyle, can be controlled. Improvement of these factors may reduce the risk of focal neuropathy and its complications.

Signs and symptoms of focal neuropathy

The symptoms of focal neuropathy are unpredictable and may appear suddenly. Some of the most common symptoms include:

  • Severe pain in the lower back or pelvis
  • Pain in the thigh
  • Pain in the chest, stomach or flank
  • Paralysis on one side of the face (Bell’s palsy)
  • Pain on the outside of the shin or inside of the foot
  • Hearing problems

When the nerves connected to the eyes are damaged from focal neuropathy, the individual may experience vision problems. These symptoms usually include:

  • Double vision
  • Blurred vision and difficulty focusing the eyes
  • Pain or aching behind one eye

If the focal neuropathy is the result of an entrapment syndrome (compressed or pinched nerve), the symptoms are usually isolated to a specific area. With carpal tunnel syndrome, the most common entrapment syndrome, the symptoms appear in the wrist or hand. Carpal tunnel syndrome results in pain, numbness or weakness in the hand and can interfere with function. Diabetes does not cause compression neuropathies, but people with diabetes are at a higher risk for developing this type of nerve damage.

The duration of the symptoms vary according to the type of nerve damage and the individual’s diabetic control. If a diabetic patient does not make an effort to alter contributing factors, the symptoms may last for several months. On the other hand, if the patient lowers glucose (blood sugar) levels and adopts a healthier lifestyle, the symptoms may disappear within several weeks. The symptoms from focal neuropathy may be very painful but usually do not cause any permanent damage. By reducing the risk factors, the patient has the best chance of reducing the severity and duration of the difficulties.

Diagnosis methods for focal neuropathy

As with all forms of neuropathy, the diagnosis of focal neuropathy is based on medical history, symptoms and a physical examination.

The factors considered important in a medical history include:

  • Diagnosis and duration of diabetes
  • First appearance of symptoms
  • Past glucose (blood sugar) levels
  • Smoking and use of alcohol
  • Family history of diabetes
  • Additional medical complications

When reviewing symptoms, the physician focuses on:

  • Description of the symptoms
  • Location in the body
  • Sudden or gradual beginning of problems
  • Change of symptoms over time
  • Factors that make symptoms better or worse (e.g., body positions, time of day)

After reviewing the medical history and symptoms, the physician conducts a physical examination. In diagnosing focal neuropathy, particular attention is paid to the thighs, feet and chest. These are the parts of the body most affected by focal nerve damage. The physician may check for pain or numbness in isolated parts of the hands and feet indicating a possible compressed nerve. This usually involves a neurological examination and a comprehensive foot exam.

Because Bell’s palsy is common with focal neuropathy, the physician examines the facial muscles for any signs of weakness or paralysis. This paralysis is on one side of the face and may appear as a drooping eye or mouth. Eyesight is also closely checked for any signs of focusing difficulties or double vision.

Several diagnostic tests may be administered to determine the damage from the focal neuropathy. These tests may include:

  • Nerve conduction velocity. Small electrodes are placed on the arms and legs and an electric current is sent into the nerve. These pulses create a tingling sensation but are not painful. The physician checks for a slow or weak response to the electrical stimulation which indicates nerve damage in that area.

  • Electromyography (EMG). Small, thin needles are inserted into muscles and the responses are recorded on an EMG machine. Although there may be some pain when the needle is inserted, it usually becomes less painful as the test is conducted. No electrical shocks or injections are given through the needle. The needles measure slower or weaker responses indicating muscle damage as the result of neuropathy.

  • Nerve biopsy or skin biopsy. These minor surgical procedures obtain a sample of nerve or skin tissue for laboratory analysis to diagnose various disorders. A skin biopsy is common, but a nerve biopsy is more complicated and used only in certain circumstances. A biopsy may help physicians identify nerve degeneration and confirm specific conditions found in neuropathy.

  • Quantitative sensory testing (QST). Hot, cold and vibrating stimulations are placed on the body to measure sensation. The individual indicates when any sensation is felt as a result of the simulation. There are no electrical shocks or needles in this test. The responses are used to evaluate the function of the small and large nerve endings, which may be damaged from neuropathy.

Based on the diagnostic tests, the physician may refer the patient to specialists for further evaluation and treatment. These specialists include:

  • Neurologist, for nervous system disorders
  • Orthopedist, for skeletal and muscle disorders
  • Cardiologist, for heart and vascular problems
  • Ophthalmologist, for eye care
  • Audiologist, for hearing assessment
  • Podiatrist, for foot care

Treatment and prevention of focal neuropathy

Because focal neuropathy is nerve specific, treatment varies according to the symptoms. Treatment of the underlying cause is the first step with neuropathies. In patients with diabetes, it is important to maintain the physician-prescribed glucose (blood sugar) level. A glycohemoglobin test result of 7 percent or less is a typical goal.

Controlling glucose helps prevent or delay the onset of neuropathy for people with diabetes. With focal neuropathy, it also means reducing or eliminating the symptoms.

Besides controlling glucose, other preventive treatments include:

  • Proper diet for weight control
  • Treating and preventing high blood pressure
  • Exercise and active lifestyle
  • Good skin care and foot care
  • Avoiding smoking and limiting use of alcohol
  • Close monitoring by medical professionals

Carpal tunnel syndrome, a common type of focal neuropathy, affects a nerve in the wrist. Often the cause is unknown, but risk of developing this painful condition can be reduced by practicing good posture and body mechanics (e.g., not bending the wrist too far up or down, relaxing the grip, taking rest breaks from tasks such as typing and use of hand tools).

The second focus of treatment is symptom relief. In focal neuropathy, pain in the torso, feet and hands may be significant. Physical and occupational therapy may help with muscle pain and weakness. In addition to exercises, the therapist may fit various splints to relieve pain, especially for compressed nerve damage in the hand.  Electrical stimulation may be provided to improve the muscle weakness in the face found in Bell’s palsy.

Physicians may recommend several over-the-counter medications, such as aspirin or other anti–inflammatory drugs, for pain relief. For severe cases, research has shown that certain antidepressant and antiseizure medications have been effective in reducing pain from neuropathy by blocking the pain receptors in the brain. Analgesic topical creams containing capsaicin may be rubbed on the skin to reduce the pain in a muscle or joint. These creams contain ingredients that produce a hot, cold or numbing sensation to calm the nerve endings and reduce discomfort.

In some cases of focal neuropathy, surgery may be an option for treatment. With a compression neuropathy, such as carpal tunnel syndrome, surgery can release the compressed nerve and reduce the pain or numbness. Other compressed nerves may benefit from surgical intervention. An orthopedic surgeon may determine if surgery is an option for treatment for the nerve damage.

Scientists are developing innovative ways of treating diabetic neuropathies, including gene therapy.

Because the symptoms from focal neuropathy are usually not longstanding, the faster the glucose is controlled in patients with diabetes, the quicker the symptoms may disappear. The risk factors for neuropathy are closely related. Improving one factor (diet and weight) will most likely improve another factor (glucose level). A healthy, active lifestyle is a cornerstone of treating and preventing focal neuropathy.

Questions for your doctor on focal neuropathy

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about focal neuropathy:

  1. Do I have, or am I at risk of developing, focal neuropathy?
  2. What tests might I need, and what do they involve?
  3. Is my focal neuropathy caused by diabetes, or is it caused or worsened by something else?
  4. Does my case involve Bell’s palsy, carpal tunnel syndrome or another condition?
  5. How can my focal neuropathy affect me?
  6. How long is my focal neuropathy likely to last?
  7. Which over-the-counter or prescription medications do you recommend for me?
  8. Do I need physical or occupational therapy?
  9. Could I need surgery if other treatments fail?
  10. How can I prevent or reduce my risk of focal neuropathy?
  11. Do I also have, or am I at risk of developing, any other forms of neuropathy?
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