Neuropathic pain is caused by damage to the peripheral nervous system, the vast communications network that transmits information from the brain and spinal cord to other parts of the body. Peripheral nerves also send sensory information back to the brain and spinal cord, such as a message that the feet are cold or a finger is burned. Damage to the peripheral nervous system interferes with these vital connections.
Some forms of neuropathy involve damage to only one nerve and are called mononeuropathies. More often though, multiple nerves affecting all limbs are affected, called polyneuropathy. Occasionally, two or more isolated nerves in separate areas of the body are affected, which is called mononeuritis multiplex.
More than 100 types of peripheral neuropathy have been identified, each with its own characteristic set of symptoms, pattern of development and prognosis. Impaired function and symptoms depend on the type of nerves – motor, sensory or autonomic – that are damaged.
In the most common forms of polyneuropathy, the nerve fibers most distant from the brain and the spinal cord malfunction first. Pain and other symptoms often appear symmetrically, for example, in both feet followed by a gradual progression up both legs. Next, the fingers, hands, and arms may become affected, and symptoms can progress into the central part of the body. Many people with diabetic neuropathy experience this pattern of nerve damage.
In acute neuropathies, such as Guillain-Barré syndrome, symptoms appear suddenly, progress rapidly and resolve slowly as damaged nerves heal. In chronic forms, symptoms begin subtly and progress slowly. Some people may have periods of relief followed by relapse. Others may reach a plateau stage where symptoms stay the same for many months or years. Some chronic neuropathies worsen over time, but very few forms prove fatal unless complicated by other diseases. Occasionally, the neuropathy is a symptom of another disorder.
Because every peripheral nerve has a highly specialized function in a specific part of the body, an array of symptoms can occur when nerves are damaged. Symptoms may include:
- Temporary numbness, tingling and pricking sensations
- Sensitivity to touch
- Muscle weakness
- Painful cramps
- Burning pain, especially at night
- Muscle loss
- Bone degeneration
- Changes in skin, hair and nails
- Loss of pain sensation
- Organ or gland dysfunction
- Inability to digest food easily
- Inability to maintain safe blood pressure levels
- Difficulty breathing
- Diarrhea, constipation or incontinence
Neuropathic pain is often worse at night, seriously disrupting sleep and adding to the emotional burden of the disorder.
Diagnosing peripheral neuropathy can be difficult because the symptoms vary. Your doctor will take an extensive patient history, perform a general physical examination and tests to identify the cause of the neuropathic disorder and conduct tests to determine the extent and type of nerve damage.
Tests may include:
- Blood tests to detect diabetes, liver or kidney dysfunction and signs of abnormal immune system activity
- A lumbar puncture to examine cerebrospinal fluid (CSF) for antibodies associated with neuropathy
- Muscle strength evaluation
- Evaluation of ability to feel vibration, light touch, temperature and pain
- CT scan
- Electromyography (EMG)
- Nerve conduction velocity (NCV)
- Nerve biopsy
- Skin biopsy
No medical treatments currently exist that can cure inherited peripheral neuropathy, but other forms of the disorder respond to therapy. Peripheral nerves can regenerate if the nerve cell has not died, and symptoms can be controlled to prevent new damage.
Your doctor may suggest that you:
- Maintain an optimal weight
- Avoid exposure to toxins
- Follow a physician-supervised exercise program
- Eat a balanced diet
- Limit or avoid alcohol consumption
- Monitor and strictly control blood glucose levels
Self-care skills such as meticulous foot care and careful wound treatment in people with diabetes and others who have an impaired ability to feel pain can alleviate symptoms and improve quality of life.
Neuropathic pain is often difficult to control. Mild pain may sometimes be alleviated by over-the-counter pain medications. Several classes of drugs are helpful to patients suffering from more severe forms of chronic neuropathic pain, including:
- Mexiletine, a drug developed to correct irregular heart rhythms
- Antiepileptic drugs, including gabapentin, phenytoin and carbamazepine
- Antidepressants, including tricyclics such as amitriptyline
- Immunosuppressive drugs such as prednisone, cyclosporine or azathioprine
- Injections of local anesthetics such as lidocaine or topic patches containing lidocaine
Surgery may provide immediate relief from mononeuropathies caused by compression or entrapment injuries. Repair of a slipped disk can reduce pressure on nerves where they emerge from the spinal cord; the removal of benign or malignant tumors can also alleviate damaging pressure on nerves. Nerve entrapment often can be corrected by the surgical release of ligaments or tendons.
The benefits of surgery should always be weighed carefully against its risks.
Source: National Institutes of Health