Diagnosing Peripheral Neuropathy
The peripheral nervous system consists of the nerves located outside of the brain and spinal cord. It is responsible for transmitting information between the brain and spinal cord and the rest of the body. For instance, the peripheral nerves might send signals to the brain that your feet are cold.
But when these nerves are damaged or destroyed, in a condition called peripheral neuropathy, the nerves’ usual function is disrupted, and you might not know that your feet are cold. Conversely, you might feel a stabbing pain even if your body hasn’t been injured. Other possible symptoms include numbness and tingling, weakness, intolerance to heat, and low blood pressure.
Diabetes is a leading cause of peripheral neuropathy in the United States. Peripheral neuropathy can also be caused by an injury, such as a back injury. Chemotherapy can cause peripheral neuropathy as well. The condition is linked to autoimmune diseases, such as rheumatoid arthritis and chronic inflammatory demyelinating polyneuropathy, and may be associated with an inherited disorder, such as Charcot–Marie–Tooth disease, which causes weakness in the lower leg and muscle atrophy in the hands.
Types and Symptoms of Nerve Damage
There are three kinds of peripheral nerves. Motor nerves transmit signals from the brain and spinal cord to the muscles and control, for example, walking and talking. Sensory nerves send information from the skin and muscles back to the brain and spinal cord so that you feel, for instance, pain from a wound. Autonomic nerves regulate involuntary actions, such as breathing and digestion.
There are more than 100 types of peripheral neuropathy. Symptoms vary with each type and depend on the nerves damaged. The most common symptom of motor nerve damage is muscle weakness. Others include painful cramps and uncontrolled muscle twitching.
Sensory nerve damage can interfere with the ability to feel pain, changes in temperature, vibrations, and touch. This often causes a general sense of numbness, especially in the hands and feet. People with sensory nerve damage may feel as if they are wearing gloves and socks even when they are not. They may have trouble coordinating complex movements, such as fastening buttons or maintaining balance.
People with autonomic nerve damage may sweat excessively or not enough, which may lead to heat intolerance, or experience a loss of bladder control, which can lead to infection or incontinence. They may also have a condition called orthostatic hypotension, the inability to control the muscles responsible for maintaining safe blood pressure levels. Low blood pressure can cause dizziness, lightheadedness, or even fainting when a person moves from a seated to a standing position.
In other situations, the nerves controlling intestinal muscle contractions are damaged. This may result in diarrhea, constipation, or incontinence. Some people may have trouble eating or swallowing because of muscle weakness.
Some people experience acute peripheral neuropathy, in which symptoms appear suddenly and progress rapidly. Others may have a chronic form, meaning symptoms continue for long periods. Some people with chronic neuropathies have periods of remission followed by relapse. Others reach a plateau, where symptoms stay unchanged for months or years.
Diagnosing peripheral neuropathy can be difficult because the symptoms vary according to the nerves involved and may be vague or overlap with those associated with other conditions. NYU Langone neurologists start by taking a medical history. They use several other tools as well.
During this exam, a doctor evaluates your mental and emotional state and your ability to communicate; your movement, muscle strength, coordination, and balance; and your vision and other senses. The doctor also tests your ability to sense vibration, light touch, body position, temperature, and pain. Testing the senses can reveal sensory nerve damage and indicate the nerves affected.
A blood test can detect conditions that may be causing peripheral neuropathy, such as diabetes, nutrient deficiencies, liver or kidney dysfunction, and abnormal immune system activity.
If your doctor suspects an underlying medical condition is contributing to your symptoms, he or she may order an MRI scan. An MRI scan uses a magnetic field and radio waves to create computerized, three-dimensional images of structures in the body.
Nerve Conduction Study
A doctor may order a nerve conduction study, which can reveal if you have nerve damage. The study measures how quickly an electrical impulse travels through a nerve and how much of the impulse is transmitted.
Nerves carry messages between your brain and muscles. A damaged nerve may take too long to conduct signals or may transmit too few signals. During a nerve conduction test, a nerve is stimulated with a mild electrical current and the response is measured from the nerve or its muscle. Several places along the nerve are tested, and the area where the response is slow or incomplete is likely to be where a nerve is damaged.
An electromyogram evaluates how the nerves and muscles work together by measuring electrical impulses along nerves, nerve roots, and muscles.
To perform this test, the doctor inserts a tiny needle—an electrode that conducts an electrical current—through the skin and into the muscle. This allows your doctor to measure the amount of electricity generated by muscle cells when activated by a nerve impulse. Damaged muscle fibers do not respond as well to a nerve impulse as normally functioning muscles do.
During a skin biopsy, a small piece of skin is removed, and nerve fiber endings are examined under a microscope. This test can help a doctor identify whether the nerves are damaged, causing sensory loss.