What is peripheral nerve & muscle diseases?
The peripheral nervous system refers to the parts of nervous system outside the central nervous system, that is, those outside the brain and spinal cord. The nerves that connect the head, face, eyes, nose, muscles, and ears to the brain and the nerves that connect the spinal cord to the rest of the body, including the 31 pairs of spinal nerves, are part of the peripheral nervous system. This system also includes more than 100 billion nerve cells that run throughout the body.
Dysfunction of peripheral nerves may result from damage to any part of the nerve:
Axon (the part that sends messages)
Body of the nerve cell
Myelin sheath (the membranes that surround the axon, enabling nerve impulses to travel quickly.
If motor nerves (which stimulate muscle action) are damaged, muscles may weaken or become paralyzed. If sensory nerves (which carry sensory information) are damaged, abnormal sensations may be felt or sensation may be lost. Some peripheral nerve disorders are progressive and fatal.
Muscle stimulation (motor neuron) disorders are characterized by progressive deterioration of the nerves and other structures involved in muscle movement. These disorders develop when motor nerves do not stimulate muscles normally.
Amyotrophic lateral sclerosis is the most common of these disorders.
Typically, muscles are weak and waste away, and movements become stiff, clumsy, and awkward.
Doctors base the diagnosis on results of electromyography, magnetic resonance imaging, and blood tests.
There is no specific treatment or cure, but drugs can help lessen symptoms.
For normal muscle function, muscle tissue and nerve connections between the brain and muscle must be normal. In muscle stimulation disorders (motor neuron disorders), motor nerves do not stimulate muscles normally. As a result, muscles weaken, waste away (atrophy), and can become completely paralyzed even though the muscles themselves are not the cause of the problem.
Muscle stimulation disorders include amyotrophic lateral sclerosis (the most common), primary lateral sclerosis, progressive pseudobulbar palsy, progressive muscular atrophy, progressive bulbar palsy, and postpolio syndrome. These disorders are more common among men and usually develop in people who are in their 50s. The cause is usually unknown. About 10% of people who have a muscle stimulation disorder have a hereditary type and thus have family members who also have the disorder.
In all of these disorders, the parts of the nervous system involved in muscle movement—including motor nerves in the spinal cord and in other parts of the body and parts of the brain—progressively deteriorate, causing muscle weakness that can progress to paralysis. However, in each disorder, a different part of the nervous system is affected. Consequently, each disorder has different effects. For example, some affect the mouth and throat first, and others affect a hand or foot first or most severely.
Muscles are affected, but people do not have pain or any changes in sensation. Depression is common.
Doctors suspect one of these disorders in adults who have progressive muscle weakness without pain or loss of sensation. Doctors ask people which parts of the body are affected, when the disorder started, what symptoms appeared first, and how the symptoms changed over time. This information gives them clues about the cause of symptoms.
Muscle weakness can have many causes, so diagnostic tests, such as the following, are needed to help narrow the possibilities:
Magnetic resonance imaging (MRI) of the brain and sometimes the spinal cord is done to check for abnormalities that may cause similar symptoms.
Electromyography which involves stimulating muscles and recording their electrical activity, can help determine whether the problem is in nerves or muscles.
Nerve conduction studies, which measures how fast nerves transmit impulses, may also be done. The speed of impulses is not affected until late in these disorders, so if impulses are unexpectedly slow, the cause of symptoms may be another disorder.
Blood tests are done to check for other disorders (such as infections and metabolic disorders) that do not affect the nerves but can cause weakness.
Muscle stimulation disorders have no specific treatment or cure. Care provided by a team of several types of health care practitioners (multidisciplinary team) helps people cope with progressive disability. Physical therapy helps people maintain muscle strength and helps prevent shortening of muscles (contractures). Nurses or other caregivers must feed people with swallowing difficulties carefully to prevent choking. Some people must be fed through a tube inserted through the abdominal wall into the stomach (gastrostomy tube).