Paralysis is the loss of movement in one or more body parts. It may be a symptom of a disease of the nerves or muscles or injury to the brain or spine. In some cases, paralysis is also accompanied by the loss of sensation in the affected area.

Patients experience varying degrees of paralysis depending on the cause. It may be permanent or temporary. It may also occur sporadically or become progressively worse, with larger portions of the body becoming impacted or attacks lasting longer. The extent of its effects on the body ranges widely. A patient may lose the ability to move all or most of the body (quadriplegia), the trunk and legs (paraplegia), the right or left side of the body (hemiplegia), or only certain muscle groups (localized paralysis).

In most cases, paralysis is a symptom of a condition that affects the ability of nerve cells (neurons) to communicate with muscles in order to initiate movement. A stroke or head injury may damage parts of the brain involved in initiating movement or transmitting signals to other portions of the body. Spinal cord injuries have the potential to reduce or sever nerve communication to large portions of the body. Injuries that damage areas higher along the spinal cord may cause paralysis over a greater portion of the body than lower spinal injuries.

Many diseases also cause nerve damage that may progress to paralysis. These include cerebral palsy, amyotrophic lateral sclerosis, and multiple sclerosis. In patients with muscular dystrophy, paralysis results from muscle degradation rather than problems with neuron function.

When paralysis occurs, it is likely to be accompanied by several other symptoms. These may include difficulty breathing, abnormal heart rhythms, blood clots, incontinence and uncontrollable limb movements (spasticity). Without proper care, patients may also experience pressure sores and bladder infections.

The cause of the paralysis helps determine any potential treatment routes. Corticosteroid medications may be given immediately following a spinal cord injury to reduce inflammation that may cause further nerve damage. Medications are also available to slow the progression of some diseases that may cause paralysis. Surgery may provide benefit to some patients who have been injured, have paralysis-causing disease, or are born with spina bifida. Physical therapy is also available to help paralyzed patients regain some mobility.