The loss of
muscular function in a part of the body,
caused by damage to the muscles themselves or to a part of the nervous system. Paralysis may vary in severity from affecting a single
small muscle to affecting most of the body.
Disease of the muscles
themselves leads more commonly to weakness than to
total paralysis. However, some
forms of muscular dystrophy, most of which occur in childhood, can progress to severe and eventually
fatal paralysis. There is no effective treatment for
these conditions.
Any
block in the transmission of impulses from nerves to muscles also may
result in paralysis. This
occurs in myasthenia gravis, in botulism, and in some other types of
poisoning (for example, with "nerve gas").
The
peripheral nerves may be
injured directly or damaged by disease, including diabetes mellitus, polyarteritis nodosa, cancer, alcoholism, vitamin deficiencies, leprosy, porphyria, and some drug reactions. This damage may lead to weakness or to total paralysis of the muscles supplied by the affected nerves.
The spinal cord may be damaged by a
number of conditions, including poliomyelitis, multiple sclerosis, and trauma. The pattern of the resulting paralysis depends on its cause. Severe
damage to the spinal cord results in paraplegia---complete
paralysis of the legs and the lower part of the body, usually
including bladder paralysis. If the spinal cord damaged is in the region of the neck, the arms may be paralyzed as well as the legs---
quadriplegia.
Brain damage also may result in paralysis. The most common
cause here is a stroke, caused by hemorrhage,
thrombosis in the brain, or impairment of cerebral
blood flow. The extent of the paralysis is variable, but the most
common pattern is partial or complete paralysis of the arm and leg on one side---
hemiplegia. Other
causes of brain damage
include meningitis, encephalitis, syphilis, and brain tumors. Transient
paralysis (Todd's paralysis) may
occur in a part of the body following an epileptic attack.
Paralysis resulting from division of a major nerve
tract in the spinal cord or brain is
permanent and irreversible, but that resulting from other
diseases may have a more variable prognosis. In "acute infective polyneritis" (the guil-lain-barré syndrome), more or less total paralysis may be followed by complete
recovery if the patient survives. In some diseases (such as strokes) the
extent of recovery is
extremely variable, while in
others (such as motor
neuron disease) recovery is unknown.
Survival in
paralysis depends on the
underlying disease and whether or not it affects the respiratory tract muscles and heart muscles. Artificial
ventilation may keep alive
patients with some diseases (for example, poliomyelitis or
acute infective polyneuritis) until the paralysis improves or remits. In some cases a person may never
recover the ability to
breathe on his own and will remain dependent on respirators for life.