Paralysis Health Article

Definition

Paralysis is defined as complete loss of strength in an affected limb or muscle group.

Description

The chain of nerve cells that runs from the brain through the spinal cord out to the muscle is called the motor pathway. Normal muscle function requires intact connections all along this motor pathway. Damage at any point reduces the brain's ability to control the muscle's movements. This reduced efficiency causes weakness, also called paresis. Complete loss of communication prevents any willed movement at all. This lack of control is called paralysis. Certain inherited abnormalities in muscle cause periodic paralysis, in which the weakness comes and goes.

The line between weakness and paralysis is not absolute. A condition causing weakness may progress to paralysis. On the other hand, strength may be restored to a paralyzed limb. Nerve regeneration or regrowth is one way in which strength can return to a paralyzed muscle. Paralysis almost always causes a change in muscle tone. Paralyzed muscle may be flaccid, flabby, and without appreciable tone, or it may be spastic, tight, and with abnormally high tone that increases when the muscle is moved.

Paralysis may affect an individual muscle, but it usually affects an entire body region. The distribution of weakness is an important clue to the location of the nerve damage that is causing the paralysis. Words describing the distribution of paralysis use the suffix "-plegia," from the Greek word for "stroke." The types of paralysis are classified by region:

• monoplegia, affecting only one limb
• diplegia, affecting the same body region on both sides of the body (both arms, for example, or both sides of the face)
• hemiplegia, affecting one side of the body
• paraplegia, affecting both legs and the trunk
• quadriplegia, affecting all four limbs and the trunk

Causes

The nerve damage that causes paralysis may be in the brain or spinal cord (the central nervous system) or it may be in the nerves outside the spinal cord (the peripheral nervous system). The most common causes of damage to the brain are:

• stroke
• tumor
• trauma (caused by a fall or a blow)
• multiple sclerosis (a disease that destroys the protective sheath covering nerve cells)
• cerebral palsy (a condition caused by a defect or injury to the brain that occurs at or shortly after birth)
• metabolic disorder (a disorder that interferes with the body's ability to maintain itself)

Damage to the spinal cord is most often caused by trauma, such as a fall or a car crash. Other conditions that may damage nerves within or immediately adjacent to the spine include:

• tumor
• herniated disk (also called a ruptured or slipped disk)
• spondylosis (a disease that causes stiffness in the joints of the spine)
• rheumatoid arthritis of the spine
• neurodegenerative disease (a disease that damages nerve cells)
• multiple sclerosis

Damage to peripheral nerves may be caused by:

• trauma
• compression or entrapment (such as carpal tunnel syndrome)
• Guillain-Barré syndrome (a disease of the nerves that sometimes follows fever caused by a viral infection or immunization)
• chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) (a condition that causes pain and swelling in the protective sheath covering nerve cells)
• radiation
• inherited demyelinating disease (a condition that destroys the protective sheath around the nerve cell)
• toxins or poisons