Spastic cerebral palsy is usually the result of an upper motor neuron lesion in the brain (often through injury or damage inflicted in the womb or during birth), though the motor cortex and corticospinal tract may also be affected. The lesion impairs the brain’s ability to send signals to the nerve receptors housed in the spine, which in turn limits the nerves’ ability to receive gamma amino butyric acid. Gamma amino butyric acid normally triggers the nerves to send messages to the muscles that cause them to work together; when one group of muscles contracts, another relaxes. The lack of this important organic compound in these damaged nerves instead causes them to send a signal to the connected muscles to tense up, or become hypertonic. In people with spastic hemiplegia, the nerve receptors that control one side of their body are more damaged than the other, so their symptoms are relatively concentrated to one side of the body. The affected side of the body is rigid, weak and has less functioning ability than the other.
Usually, the upper extremities are affected more than the lower extremities in people with spastic hemiplegia. In some cases, however, both arms are equally affected, in which case the condition is known as double hemiplegia.
The degree of disability and level of functioning are dependent on the extent of damage to the brain and connecting nerve receptors. Some people with spastic hemiplegia lead independent, productive lives, while others need assistance and have difficulty performing everyday tasks. Many people with spastic hemiplegia undergo physical and occupational therapy to help strengthen muscle tissue, increase range of motion and help them build essential skills they need to function on their own as much as possible. Braces may also be used to either stabilize the affected limb or to limit the use of the non-affected limb so that the person is forced to use the affected limb more, thus strengthening it.