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

DESCRIPTION
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:

Trama
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

SYMPTOMS

The distribution of paralysis offers important clues to the site of nerve damage. Hemiplegia is almost always caused by brain damage on the side opposite the paralysis, often from a stroke. Paraplegia occurs after injury to the lower spinal cord, and quadriplegia occurs after damage to the upper spinal cord at the level of the shoulders or higher (the nerves controlling the arms leave the spine at that level). Diplegia usually indicates brain damage, most often from cerebral palsy. Monoplegia may be caused by isolated damage to either the central or the peripheral nervous system. Weakness or paralysis that occurs only in the arms and legs may indicate demyelinating disease. Fluctuating symptoms in different parts of the body may be caused by multiple sclerosis.

Sudden paralysis is most often caused by injury or stroke. Spreading paralysis may indicate degenerative disease, inflammatory disease such as Guillain-Barré syndrome or CIDP, metabolic disorders, or inherited demyelinating disease.

Other symptoms often accompany paralysis from any cause. These symptoms may include numbness and tingling, pain, changes in vision, difficulties with speech, or problems with balance. Spinal cord injury often causes loss of function in the bladder, bowel, and sexual organs. High spinal cord injuries may cause difficulties in breathing.

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