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Hemiplegia is a form of paralysis that affects just one side of the body, often just one arm and one leg, but occasionally with symptoms extending partially into the torso. A related condition, hemiparesis, is significant loss of strength and mobility on one side of the body, but without full paralysis. Some people with hemiplegia develop the condition after a bout of hemiparesis. Others may alternate between times of hemiparesis and hemiplegia.

What is Hemiplegia?

The brain is divided into two hemispheres, separated by a bundle of fibers called the corpus callosum. Generally speaking, the right side of the brain controls muscles and other functions on the left side of the body, while the left side of the brain controls much of the right side of the body. Thus hemiplegia and hemiparesis almost always indicate a problem with one side of the brain.

Hemiplegia may come on suddenly, or develop slowly over time. A condition related to hemiplegia, spastic hemiplegia, causes the muscles to get stuck in a contraction, resulting in little muscle control, chronic muscle pain, and unpredictable movements. People with hemiplegia often show other signs of brain damage or head injury, and may experience issues with other areas of their bodies.

Hemiplegia, like other forms of paralysis, is characterized by significant loss of sensation and control in the affected area. People with hemiplegia may experience intermittent pain, and may be better able to control their limbs at some times than at others.

What Causes Hemiplegia?

Though the arms, legs, and possibly torso are the regions of the body most obviously affected by hemiplegia, in most cases of hemiplegia these body regions are actually perfectly healthy. Instead, the problem resides in the brain, which is unable to produce, send, or interpret signals due to disease or trauma-related damage. Less frequently, hemiplegia results from damage to one side of the spinal cord, but these sorts of injuries more typically produce global problems, not just paralysis on one side of the body.

Some common causes of hemiplegia include:

  • Traumatic brain injuries to one side of the brain only. These may be caused by car accidents, falls, acts of violence, and other factors.
  • Cardiovascular problems, particularly aneurysms and hemorrhages in the brain.
  • Strokes and transient ischemic attacks (better known as TIA or mini-strokes).
  • Infections, particularly encephalitis and meningitis. Some serious infections, particularly sepsis and abscesses in the neck, may spread to the brain if left untreated.
  • Conditions that cause demyelination of the brain, including multiple sclerosis and some other autoimmune diseases.
  • Reactions to surgery, medication, or anesthesia.
  • Loss of oxygen to the brain due to choking or anaphylactic shock.
  • Brain cancers.
  • Lesions in the brain, even if non-cancerous, since these lesions can impede function on one side of the brain.
  • Congenital abnormalities, including cerebral palsy and neonatal-onset multi-inflammatory disease.
  • Rarely, psychological causes; some states of catatonia can cause hemiplegia, and people with parasomnia—a sleep disorder leading to unusual nighttime behavior—may experience nighttime episodes of hemiplegia.

How Does Hemiplegia Affect the Body?

The course of hemiplegia is highly variable, and heavily dependent on the cause. For many people with hemiplegia, the condition is a temporary one, but others may struggle with hemiplegia for the rest of their life. For some, the paralysis is extensive and complete, producing a total loss of sensation and bodily control. For others, symptoms are less severe. Some of the ways hemiplegia affects the body include:

  • Total or partial loss of sensation on just one side. 
  • Changes in cognition, mood, or perception. 
  • Difficulty speaking. 
  • Changes on the other side of the body, since those muscles may begin to atrophy or become painful due to chronic muscle spasms. 
  • Spastic attacks during which the muscles move without your conscious control. 
  • Seizures. 
  • “Pusher syndrome.” With this symptom, people with hemiplegia shift their weight to the paralyzed side of the body, resulting in significant loss of motor control. 

How is Hemiplegia Treated?

There's no single treatment approach that works for all people. Instead, treatment is largely dependent on the cause of hemiplegia. Some treatment options include:

  • Blood thinners to reduce cardiovascular blockages and decrease the chances of future strokes.
  • Antibiotics, usually delivered intravenously, to combat brain infections.
  • Surgery to remove swelling on the brain or objects lodged in the brain.
  • Muscle relaxant drugs.
  • Surgery to address secondary issues, particularly involuntary muscle contractions, spinal damage, or damage to the ligaments or tendons on the unaffected side of the body.
  • Physical therapy designed to help the brain work around the injuries. Physical therapy can also strengthen the unaffected side and help you reduce the loss of muscle control and tone.
  • Support groups, family education, and advocacy.
  • Psychotherapy to help you deal with the psychological effects of the disease.
  • Exercise therapy to help you remain healthy in spite of your disability.