What is peripheral neuropathy?
Peripheral neuropathy is a term which describes the damage done to peripheral nerves. This damage can be caused by more than 100 different known diseases. If only one nerve is involved it is called a mononeuropathy an example of which is carpal tunnel syndrome. If 2 or more nerves are involved in separate areas it is called a multiple mononeuropathy. This is usually the type of neuropathy meant when people say they have a peripheral neuropathy. If a spinal nerve root is involved it is called a radiculopathy such as sciatica from a herniated disc. If there is diffused involvement of the peripheral nerves it is called a polyneuropathy.
What is damaged in peripheral neuropathies?
The symptoms of peripheral neuropathy occur because the nerves are damaged in some way. This can occur at either the axon, which is “wire” from the nerve cell out to the body, or it can occur in the myelin sheath itself. The myelin sheath is like an insulator around the axon which acts to speed conduction of the nerve signal. For example, an axon with myelin connects like a broadband internet connection able to stream high definition video and an axon without myelin is like dial up service, slow with frequent interruptions. Myelin involvement often occurs in the setting of demyelinating diseases or some infections.
In addition to damaging the axon or myelin or both, peripheral neuropathy can also affect a variety of nerve types. Small nerves fibers are often damaged in diseases such as diabetes which leads to problems with pain, temperature, and sensation changes. Large nerve fibers are injured in such disease processes like Guillan-Barre syndrome which leads to profound muscle weakness. Nerve fibers that come directly from the brain, called cranial nerves, can also be injured by a variety of disease processes.
The type of symptoms you experience from peripheral neuropathy depend on the underlying cause and the type and location of the nerves damaged. For causes from metabolic disorders such as diabetes, the progession is usually slow and begins in the lower extremities. A change in sensation is often the first symptom people notice. This is worse at night. It progresses from there to involve decreases in the ability to sense temperature, vibration, and eventually leads to complete sensory loss. Oddly enough this is frequently accompanied by severe pain in the affected extremity which can be brought on by even minimal stimuli. At its ends stage, peripheral neuropathy can lead to skin breakdown, balance problems, and ultimately profound muscle weakness and wasting.
What are some of the definitions of medical terms used to describe peripheral neuropathy?
The follow is a list of common definitions:
- Paresthesia: this is often described as numbness or tingling or the pins and needle type sensation.
- Anesthesia: this is loss of all sensation, pain, temperature, touch. If you have this you could cut off your finger and not feel it at all.
- Analgesia: this is loss of all painful sensation but you can still feel things such as touch and temperature.
- Hyperesthesia: this is increased sensitivity to any kind of stimulus to the skin
- Hypoesthesia: this is decreased sensitivity
How is peripheral neuropathy diagnosed?
The diagnosis of peripheral neuropathy includes an evaluation by a physician. This evaluation will include a history of your symptoms, a physical exam, and in some cases diagnostic testing.
The history of your symptoms will often lead to the diagnosis and can point to or pinpoint a cause. Important items will include when the symptoms started. Did they start suddenly or gradually or has it been a long slow process developing over an extended period of time. Is there just one episode or does it come and go. Other important factors include underlying medical disorders such as cancer, diabetes, kidney failure, dietary habits, trauma, employment exposures, and family history of a similar problem.
The physical exam helps to define the extent of the neuropathy and usually involves a head to toe evaluation with particular attention on the eye and neurologic portions of the exam. During this exam it is usually evident if you have a mononeuropathy or a polyneuropathy. After the history and physical exam diagnostic testing is often undertaken. There are three main classes of diagnostic tests used to aid in the diagnosis and treatment. These are laboratory studies, imaging studies, and nerve studies.
Laboratory studies will often include a complete blood count to look for signs of anemia, heavy metal poisoning, or cancer. Electrolytes, kidney function tests, and certain vitamin levels will often be checked to evaluated causes such as kidney failure, diabetes and other endocrine disorders, and nutritional deficiencies. In some cases screening tests for rare diseases such as porphyria or infections will also be done and at times may include a skin or nerve biopsy or a lumbar puncture (spinal tap).
Imaging studies may include but are not limited to CT scans and MRI of the affected area. MRI in particular can often tell, in the right context, if your symptoms are from nerve impingement or other structural disorder.
Finally, nerve conduction studies and electromyography(EMG) is often undertaken. In nerve conduction studies a probe is used to stimulate a nerve causing an electrical impulse to fire. The way in which this impulse is transmitted can often tell your doctor if it is the axon or the myelin that is damaged. With EMG electrical activity is measure with the muscle active and at rest. This can help distinguish between nerve and muscle injury.
What kind of treatments are available for peripheral neuropathy?
The approach to treating peripheral neuropathy can be broken down into three main areas.
- First, correcting the underlying cause of the neuropathy is important. Peripheral nerves, to some extent can heal and regenerate, so if the cause is found early, and treatment is initiated then the disease process can be slowed, stopped, or sometimes even reversed. For example, while diabetes can cause peripheral neuropathy, early diagnosis with tight control of your blood sugar can prevent this complication from occurring and stop or even reverse it once it has started.
- Second, it is important to create on optimal environment for healing within your body. This begins with adopting a healthy lifestyle. Sleep is essential for your body to heal itself and trying to get 8 hours of sleep a night is very important. Maintaining an optimal body weight through healthy diet and exercise is also necessary. Get rid of the junk that you eat focusing on fruits, vegetables, and whole grains while limiting processed and high fat foods. This is usually enough to correct any underlying nutritional deficiencies but you may also want to consider taking a multivitamin. Finally, limit or eliminate alcohol and definitely stop tobacco in any of its forms.
- Third, it is important to control the symptoms. The symptoms of peripheral neuropathy can be very difficult to control. Initial pain control with over the counter analgesics such as ibuprofen and acetaminophen is sometimes helpful but rarely sufficient. If pain is severe and chronic a variety of medications may be tried but there are no definitive guidelines give lack of evidence strongly favoring one treatment over another.
- Tricyclic antidepressants. These medications are older antidepressants largely replaced now by the SSRI (selective serotonin reuptake inhibitors). An example is amitriptyline which has been shown to be of some benefit and is thought to work by affecting the way your nerves respond to pain.
- Antiepileptics. These are seizure medications such as phenytoin, carbamazepine, oxcarbazepine, lamictal, and topiramate. They have shown some benefit with the exception of topiramate. To some extent they work by blocking the ability of nerves to rapidly trigger and electrical response.
- Gabapentin. This drug is also a seizure medication but its mechanism of action is not definitively known. It is thought to help peripheral neuropathy by modulating pain signals in the the spinal cord.
- Tramadol: This is a pain medication which has been found to have some benefit beyond its ability to treat pain in helping with the symptoms of peripheral neuropathy.
- Lidocaine patches: Known also as lidoderm patches these are applied directly to the site of pain and help in select cases.
- Capsaicin: A topical preparation shown to have some benefit.
- Surgical intervention: In extreme cases sometimes the nerve itself will be destroyed. This often only helps the pain for a brief period of time as peripheral nerves have an astounding ability to regenerate. Unfortunately, symptoms ultimately wind up worse then before the procedure.
What does the future hold?
As with any disease prevention is always better then treatment. There are multiple ongoing investigations into the different ways in which the nerves are damaged. As these processes are identified it is hoped that additional treatment will be found. Other research areas include looking at how the body responds to pain from neuropathy and creating or finding treatments that will block this process at either the brain or in the spinal cord.