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


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 and symptoms


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


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.


Careful attention should be paid to any events in the patient's history that might reveal the cause of the paralysis. The examiner should look for incidents such as falls or other traumas, exposure to toxins, recent infections or surgery, unexplained headache, preexisting metabolic disease, and family history of weakness or other neurologic conditions. A neurologic examination tests strength, reflexes, and sensation in the affected area and normal areas.
Imaging studies, including computed tomography scans (CT scans), magnetic resonance imaging (MRI) scans, or myelography may reveal the site of the injury. Electromyography and nerve conduction velocity tests are performed to test the function of the muscles and peripheral nerves.


The only treatment for paralysis is to treat its underlying cause. The loss of function caused by long-term paralysis can be treated through a comprehensive rehabilitation program. Rehabilitation includes:
  • Physical therapy. The physical therapist focuses on mobility. Physical therapy helps develop strategies to compensate for paralysis by using those muscles that still have normal function, helps maintain and build any strength and control that remain in the affected muscles, and helps maintain range of motion in the affected limbs to prevent muscles from shortening (contracture) and becoming deformed. If nerve regrowth is expected, physical therapy is used to retrain affected limbs during recovery. A physical therapist also suggests adaptive equipment such as braces, canes, or wheelchairs.
  • Occupational therapy. The occupational therapist focuses on daily activities such as eating and bathing. Occupational therapy develops special tools and techniques that permit self-care and suggests ways to modify the home and workplace so that a patient with an impairment may live a normal life.
  • Other specialties. The nature of the impairment may mean that the patient needs the services of a respiratory therapist, vocational rehabilitation counselor, social worker, speech-language pathologist, nutritionist, special education teacher, recreation therapist, or clinical psychologist.


The likelihood of recovery from paralysis depends on what is causing it and how much damage has been done to the nervous system.


Prevention of paralysis depends on prevention of the underlying causes. Risk of stroke can be reduced by controlling high blood pressure and cholesterol levels. Seatbelts, air bags, and helmets reduce the risk of injury from motor vehicle accidents and falls. Good prenatal care can help prevent premature birth, which is a common cause of cerebral palsy.



Bradley, Walter G., et al., editors. Neurology in Clinical Practice. 2nd ed. Boston: Butterworth-Heinemann, 1996.

Key terms

Computed tomography (CT) — An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures.
Electromyography — A test that uses electrodes to record the electrical activity of muscle. The information gathered is used to diagnose neuromuscular disorders.
Magnetic resonance imaging (MRI) — An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct images of internal structures.
Myelin — The insulation covering nerve cells. Demyelinating disease causes a breakdown of myelin.
Myelography — An x-ray process that uses a dye or contrast medium injected into the space around the spine.
Nerve conduction velocity test — A test that measures the time it takes a nerve impulse to travel a specific distance over the nerve after electronic stimulation.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


 [pah-ral´ĭ-sis] (pl. paral´yses.)
Loss or impairment of motor function in a part due to a lesion of the neural or muscular mechanism; also, by analogy, impairment of sensory function (sensory paralysis). Paralysis is a symptom of a wide variety of physical and emotional disorders rather than a disease in itself. Called also palsy.
Types of Paralysis. Paralysis results from damage to parts of the nervous system. The kind of paralysis resulting, and the degree, depend on whether the damage is to the central nervous system or the peripheral nervous system.

If the central nervous system is damaged, paralysis frequently affects the movement of a limb as a whole, not the individual muscles. The more common forms of central paralysis are hemiplegia (in which one entire side of the body is affected, including the face, arm, and leg) and paraplegia (in which both legs and sometimes the trunk are affected). In central paralysis the tone of the muscles is increased, causing spasticity.

If the peripheral nervous system is damaged, individual muscles or groups of muscles in a particular part of the body, rather than a whole limb, are more likely to be affected. The muscles are flaccid, and there is often impairment of sensation.
Causes of Central Paralysis. stroke syndrome is one of the most common causes of central paralysis. Although there is usually some permanent disability, much can be done to rehabilitate the patient. Paralysis produced by damage to the spinal cord can be the result of direct injuries, tumors, and infectious diseases. Paralysis in children may be a result of failure of the brain to develop properly in intrauterine life or of injuries to the brain, as in the case of cerebral palsy. Congenital syphilis may also leave a child partially paralyzed. Paralysis resulting from hysteria has no organic basis and is a result of emotional disturbance or mental illness.
Causes of Peripheral Paralysis. Until the recent development of immunizing vaccines, the most frequent cause of peripheral paralysis in children was poliomyelitis. neuritis, inflammation of a nerve, can also produce paralysis. Causes can be physical, as with cold or injury; chemical, as in lead poisoning; or disease states, such as diabetes mellitus or infection. Paralysis caused by neuritis frequently disappears when the disorder causing it is corrected.
paralysis of accommodation paralysis of the ciliary muscles of the eye so as to prevent accommodation.
paralysis a´gitans Parkinson's disease.
ascending paralysis spinal paralysis that progresses upward.
birth paralysis that due to injury received at birth.
brachial paralysis paralysis of an upper limb from damage to the brachial plexus.
bulbar paralysis that due to changes in motor centers of the medulla oblongata; the chronic form is marked by progressive paralysis and atrophy of the lips, tongue, pharynx, and larynx, and is due to degeneration of the nerve nuclei of the floor of the fourth ventricle.
central paralysis any paralysis due to a lesion of the brain or spinal cord.
cerebral paralysis paralysis caused by an intracranial lesion; see also cerebral palsy.
compression paralysis that caused by pressure on a nerve.
conjugate paralysis loss of ability to perform some parallel ocular movements.
crossed paralysis paralysis affecting one side of the face and the other side of the body.
crutch paralysis brachial paralysis caused by pressure from a crutch.
decubitus paralysis paralysis due to pressure on a nerve from lying for a long time in one position.
divers' paralysis decompression sickness.
Erb-Duchenne paralysis paralysis of the upper roots of the brachial plexus due to destruction of the fifth and sixth cervical roots, without involvement of the small muscles of the hand. Called also Erb's palsy.
facial paralysis weakening or paralysis of the facial nerve, as in bell's palsy.
familial periodic paralysis a hereditary disease with recurring attacks of rapidly progressive flaccid paralysis, associated with a fall in (hypokalemic type), a rise in (hyperkalemic type), or normal (normokalemic type) serum potassium levels; all three types are inherited as autosomal dominant traits.
flaccid paralysis paralysis with loss of muscle tone of the paralyzed part and absence of tendon reflexes.
immunologic paralysis former name for immunologic tolerance.
infantile paralysis the major form of poliomyelitis.
infantile cerebral ataxic paralysis a congenital condition due to defective development of the frontal regions of the brain, affecting all extremities.
ischemic paralysis local paralysis due to stoppage of circulation.
Klumpke's paralysis (Klumpke-Dejerine paralysis) atrophic paralysis of the lower arm and hand, due to lesion of the eighth cervical and first dorsal thoracic nerves.
Landry's paralysis Guillain-Barré syndrome.
lead paralysis severe peripheral neuritis with wristdrop, due to lead poisoning.
mixed paralysis combined motor and sensory paralysis.
motor paralysis paralysis of the voluntary muscles.
musculospiral paralysis Saturday night paralysis.
obstetric paralysis birth paralysis.
periodic paralysis
1. any of various diseases characterized by episodic flaccid paralysis or muscular weakness.
progressive bulbar paralysis the chronic form of bulbar paralysis; called also Duchenne's disease or paralysis.
pseudobulbar muscular paralysis pseudohypertrophic muscular dystrophy.
pseudohypertrophic muscular paralysis pseudohypertrophic muscular dystrophy.
radial paralysis Saturday night paralysis.
Saturday night paralysis paralysis of the extensor muscles of the wrist and fingers, so called because of its frequent occurrence in alcoholics. It is most often due to prolonged compression of the radial (musculospiral) nerve, and, depending upon the site of nerve injury, is sometimes accompanied by weakness and extension of the elbow. Called also musculospiral or radial paralysis.
sensory paralysis loss of sensation resulting from a morbid process.
sleep paralysis paralysis occurring at awakening or sleep onset; it represents extension of the atonia of REM sleep into the waking state and is often seen in those suffering from narcolepsy or sleep apnea. Called also waking paralysis.
spastic paralysis paralysis with rigidity of the muscles and heightened deep muscle reflexes and tendon reflexes.
spastic spinal paralysis lateral sclerosis.
tick paralysis progressive ascending flaccid motor paralysis following the bite of certain ticks, usually Dermacentor andersoni; first seen in children and domestic animals in the northern Pacific region of North America, and now seen in other parts of the world.
Volkmann's paralysis ischemic paralysis.
waking paralysis sleep paralysis.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


, pl.


(pă-ral'i-sis, -sēz),
1. Loss of power of voluntary movement in a muscle through injury or disease of it or its nerve supply.
2. Loss of any function, as sensation, secretion, or mental ability.
[G. fr. para- + lysis, a loosening]
Farlex Partner Medical Dictionary © Farlex 2012


n. pl. paraly·ses (-sēz′)
a. Loss or impairment of the ability to move a body part, usually as a result of damage to its nerve supply.
b. Loss of sensation over a region of the body.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Neurology The loss of voluntary movement–motor/ muscle function due to injury or disease of the nervous system which may be partial–palsy or total, such as in botulism. See Ascending tick paralysis, Fetal paralysis, Flaccid paralysis, Laryngeal paralysis, Periodic paralysis, Sleep paralysis, Spastic paralysis, Tick paralysis, Tourniquet paralysis, Unilateral vocal cord paralysis, Vocal cord paralysis.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


, pl. paralyses (păr-al'i-sis, -sēz)
1. Loss of power of voluntary movement in a muscle through injury to or disease of its nerve supply.
2. Loss of any function, such as sensation, secretion, or mental ability.
[G. fr. para- + lysis, a loosening]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


Temporary or permanent loss of the power of movement of a part of the body (motor function). Paralysis may be due to damage to the nerves tracts or peripheral nerves carrying motor impulses to the muscles to cause them to contract or may be due to disorders of the muscles themselves. In the former case, the damage is most commonly within the brain or the spinal cord. Paralysis of one half of the body is called HEMIPLEGIA. Paralysis of the legs and lower part of the body is called PARAPLEGIA. Paralysis of all four limbs is called QUADRIPLEGIA.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


Loss of action of a muscle due to injury or disease of that muscle or its nerve supply. See palsy.
abducens paralysis See paralysis of the sixth nerve.
paralysis of accommodation See paralysis of accommodation.
paralysis of convergence A condition characterized by an inability of the eyes to converge while all other monocular eye movements are unaffected. The patient notices diplopia in near vision, which usually occurs suddenly. It is presumably due to some lesion in the nuclei responsible for convergence, as may happen in tabes dorsalis or Parkinson's disease.
divergence paralysis A condition characterized by an inability of the eyes to diverge while all other monocular eye movements are unaffected. It is characterized by a sudden development of diplopia with marked esotropia at distance and sometimes headaches. The key difference with divergence insufficiency is the sudden onset of symptoms. Its association includes encephalitis, multiple sclerosis, head trauma, cerebral haemorrhage, brain tumour and vascular lesions of the brainstem.
paralysis of the fourth nerve A condition characterized by a hypertropia of the eye with the affected superior oblique muscle. It may be due to a lesion of the fourth cranial nerve or its nucleus as a result of injury (the most common cause), vascular lesions, aneurysm or tumour. The patient usually presents with an abnormal head posture to avoid diplopia. If the condition does not recover by itself following therapy of the underlying cause, surgery is usually the only alternative treatment. Syn. trochlear paralysis. See abnormal head posture; trochlear nerve; paralytic strabismus.
oculomotor paralysis See paralysis of the third nerve.
paralysis of the sixth nerve A condition characterized by an esotropia of the eye with the affected lateral rectus muscle. It may be due to a lesion of the sixth cranial nerve or its nucleus as a result of a vascular disease (e.g. diabetes, hypertension), injury, or tumour. The patient presents with an abnormal head turn to avoid diplopia. If the condition does not recover by itself following therapy of the underlying cause, surgery is usually the only alternative treatment. Syn. abducens paralysis; lateral rectus palsy. See abnormal head posture; abducens nerve; paralytic strabismus; Gradenigo's syndrome; transposition.
paralysis of the third nerve A condition that leads to a wide impairment of motor function, as this nerve innervates most of the muscles of the eye. It may be due to a vascular disease (e.g. diabetes, hypertension), aneurysm (especially of the internal carotid artery), injury or tumour. In total paralysis only the lateral rectus and the superior oblique muscles will be spared and the eye will be in a position of abduction, slight depression and intorsion. Ptosis will also be present and the pupil will be dilated and non-reactive, and there will also be paralysis of accommodation. If the condition does not recover by itself following therapy of the underlying cause, surgery is usually the only alternative. Syn. oculomotor paralysis. See circle of Willis; oculomotor nerve; ophthalmoplegia; paralytic strabismus; Benedikt's syndrome; Weber's syndrome; forced duction test; transposition.
trochlear paralysis See paralysis of the fourth nerve.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


, pl. paralyses (păr-al'i-sis, -sēz)
1. Loss of power of voluntary movement in a muscle through injury or disease of it or its nerve supply.
2. Loss of any function.
[G. fr. para- + lysis, a loosening]
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about paralysis

Q. What Is Bell's Palsy? A friend of mine has been told she has Bell's palsy. What happens in this disease?

A. Bell's palsy is defined as an idiopathic (from an unknown reason) unilateral facial nerve paralysis, usually self-limiting. The trademark is rapid onset of partial or complete palsy, usually in a single day.
Here you can learn more about what exactly is Bell's palsy-

Q. What are the causes of bell's palsy?

A. I had it 5 years ago at age 20. All the symptoms of the above are correct not to mention the tiredness and rapid blinking of the eye from the effected side.

In my case I have just found out that I have a non milignate tumor behind my left eye which was likely to be the cause of the Bell Pausy in the first place. I encourage anyone who has symptoms or pain spanning more than 8 weeks to see their doctor and if possible request request or demand a MRI scan for peace of mind.

If pain persists get a second opinion and dont let the Dr. shrugg you off.

Q. I go to sleep & use to wake up paralyzed in my sleep. I go to sleep & use to wake up paralyzed in my sleep. But not asleep, just laying there, eyes wide open paralyzed. I couldn't breath, I couldn't speak, move anything but my eyes. I could look around but I couldn't even breathe. This has happened a few times in my old house, once in my mother's house (she lived by the side of a graveyard), and then only once in my new house. What is it and what do you think is causing it?

A. I had the same problem but never at night...and it only happened during the day when I take nap. I will wake up and I can't move or talk, I can't open my eyes either. I've never been able to snap out of it though, I just have to lay there until I go back to sleep, and usually it doesn't happen when I wake up the next time. Needless to say I try NOT to take naps anymore, because it happens nearly every time.

More discussions about paralysis
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