Peripheral neuropathy is a disease characterized by damage to the peripheral nerves, the nerves that carry information and messages from the brain and spinal cord to the body. There are three main types of peripheral nerves: motor, sensory and autonomic. Symptoms depend upon the type of nerve affected and the location of the damage.

The motor nerves control conscious movement of muscles. Damage to these nerves can affect walking or the ability to grasp objects. Patients may also develop muscle spasms or cramps, bone loss and changes in the skin, hair or nails.

The sensory nerves transmit signals related to the senses, like touch. Damage to these nerves can interfere with the ability to feel pain (like from a cut or burn) or cause numbness in the hands or feet. Sensory neuropathy can also impair the ability to feel the location of the feet or hands, causing problems with walking, balance or buttoning clothing. In some cases, the nerve receptors are oversensitive, causing severe pain from a slight touch.

The autonomic nerves regulate unconscious functions, like breathing, digestion and heart rate. Damage to these nerves can cause an inability to sweat, loss of bladder control and an inability to maintain safe blood pressure levels. In severe cases, autonomic peripheral neuropathy can cause life-threatening problems, like irregular heart rhythms or breathing problems.

The Neuropathy Association estimates up to 20 million Americans have peripheral neuropathy. The condition can be acquired or inherited. The most common cause of acquired peripheral neuropathy in the U.S. is diabetes. The American Diabetes Association estimates 60 to 70 percent of Americans with diabetes have some degree of peripheral neuropathy. In severe cases, patients may develop poorly healing wounds that require amputation.

The most common form of inherited peripheral neuropathy is Charcot-Marie-Tooth (CMT) disease. This condition affects the motor and sensory nerves, causing them to slowly degenerate. The muscles become weak and patients gradually lose the ability to use their arms and legs. Some patients also lose the ability to feel temperature and pain. In rare cases, CMT can lead to hearing loss and weakness of the respiratory muscles. The Charcot-Marie-Tooth Association estimates about 2.6 million Americans have CMT.

Tracking the Course of Neuropathy

There is no cure for inherited forms of peripheral neuropathy. However, there are some treatments that can ease the symptoms of acquired neuropathy. Doctors need to periodically assess the health of the affected nerves to determine if treatments are working or more aggressive interventions are needed.

One test is called electromyography. A tiny needle is inserted into a muscle to compare the amount of electrical activity in the muscle during rest and contraction. This helps doctors differentiate between muscle and nerve disease.

In nerve conduction velocity, a probe is used to electrically stimulate a target nerve, causing the nerve to generate its own signal. The signal is received by an electrode placed further along the nerve route. A slower conduction time or reduction in the strength of the signal may be an indication of nerve damage.

A nerve biopsy is the removal of a small piece of the affected nerve for examination under a microscope. It is a very invasive procedure that, on its own, can increase the risk for nerve damage.

A skin biopsy is the removal of a thin section of skin. Using a microscope, doctors count the number of nerve endings and examine their health. The test provides an indication of the health of the small nerve fibers. Although still a surgical procedure, it is less invasive and easier to perform than a nerve biopsy.

A New Technique

Researchers at the University of Rochester Medical Center are testing another technique to study the health of peripheral nerves, called reflectance confocal microscopy. A special laser beam is aimed at the skin on the tip of the finger. The light from the laser is reflected back, illuminating tiny structures on the skin, called Meissner corpuscles. Neurologist David Herrmann, M.D., says these corpusles encapsulate the endings of very small nerves, acting like tiny touch sensors. The number and density of these corpuscles may be an indication of the health of the peripheral nerves.

In a small study, Herrmann used reflectance confocal microscopy to look at the skin on the pinky fingers of 15 volunteers, 10 with healthy nerves and 5 with some type of neuropathy. The investigators found the healthy participants had many more Meissner corpuscles than those with neuropathy (12 corpuscles per square millimeter for healthy volunteers vs. 2.8 for those with neuropathy).

Herrmann says the small study shows reflectance confocal microscopy can be a useful tool in detecting the health of the peripheral nerves and tracking the progression of the peripheral neuropathy. It requires no cutting and no extra lab work for examination of tissue. Researchers are now using reflectance confocal microscopy to follow the treatment and progress of patients with CMT.

For general information on peripheral neuropathy:

The Neuropathy Association

For information about diabetes:

American Diabetes Association

National Institute of Diabetes and Digestive and Kidney Diseases

For information about Charcot-Marie-Tooth Disease:

Charcot-Marie-Tooth Association