Hemiplegia is not an uncommon medical disorder. In elderly individuals, strokes are the most common cause of hemiplegia. In children, the majority of cases of hemiplegia have no identifiable cause and occur with a frequency of about one in every thousand births. Experts indicate that the majority of cases of hemiplegia that occur up to the age of two should be considered to be cerebral palsy until proven otherwise.

The most common cause of hemiplegia is a cerebrovascular accident, also known as a stroke. Strokes can cause a variety of movement disorders, depending on the location and severity of the lesion. Hemiplegia is common when the stroke affects the corticospinal tract. Other causes of hemiplegia include spinal cord injury, specifically Brown-Séquard syndrome, traumatic brain injury, or disease affecting the brain. As a lesion that results in hemiplegia occurs in the brain or spinal cord, hemiplegic muscles display features of the Upper Motor Neuron Syndrome. Features other than weakness include decreased movement control, clonus (a series of involuntary rapid muscle contractions), spasticity, exaggerated deep tendon reflexes and decreased endurance.

It is well known that the incidence of hemiplegia is a lot higher in premature babies than term babies. There is also a high incidence of hemiplegia during pregnancy and experts believe that this may be related to either a traumatic delivery, use of forceps or some event which causes brain injury.

Hemiplegia in adults include trauma, bleeding, brain infections and cancers. Individuals who have uncontrolled diabetes, hypertension or those who smoke have a higher chance of developing a stroke. Weakness on one side of the face may occur and may be due to a viral infection, stroke or a cancer.

=== Medial medullary syndrome

The exact cause of hemiplegia is not known in all cases, but it appears that the brain is deprived of oxygen and this results in the death of neurons. When the corticospinal tract is damaged, the injury is usually manifested on the opposite side of the body. For example if one has an injury to the right side of the brain, the hemiplegia will be on the left side of the body.

Hemiplegia means severe weakness of the limbs on one side of the body but the specific features can vary tremendously from person to person. Problems may include:

Hemiplegia is identified by clinical examination by a health professional, such as a physiotherapist or doctor. Radiological studies like a CT scan or magnetic resonance imaging of the brain should be used to confirm injury in the brain and spinal cord, but alone cannot be used to identify movement disorders. Individuals who develop seizures may undergo tests to determine where the focus of excess electrical activity is.

Treatment should be based on assessment by the relevant health professionals, including physiotherapists, doctors and occupational therapists. Muscles with severe motor impairment including weakness need these therapists to assist them with specific exercise, and are likely to require help to do this.

Drugs can be used to treat issues related to the Upper Motor Neuron Syndrome. Drugs like Librium or Valium could be used as a relaxant. Drugs are also given to individuals whom have recurrent seizures, which may be a separate but related problem after brain injury.