Paralysis also called palsy, is defined as "loss or impairment of voluntary muscular power."
In general, diseases that produce paralysis can be divided into two groups; those that involve changes in the makeup of nervous or muscular tissue or those that are the result of metabolic disturbances in the function of nerves or muscles. Some diseases affect the entire body while others hit only a small area of the body.
At times, only one side of the body may be involved, producing a condition known as hemiplegia. In other instances both sides of the body may suffer the effects leading to diplegia or bilateral hemiplegia. When only the lower limbs are affected by paralysis it is called paraplegia. When all four limbs are affected, it is referred to as quadriplegia. How much of the body is affected depends on the site of the neurological damage. Strokes, brain tumors, etc. classically cause such extensive loss of function. In instances of inflammation of nervous tissue such as occurs in polio, specific nerve cells are damaged leading to paralysis and muscle wasting.
Various diseases that affect muscle tissue are encountered much less often that those that affect nervous tissue. These are often hereditary, and due to a disturbance of muscle metabolism. Most cases of paralysis of muscular origin, therefore, usually begin early in life. However, other diseases can occur at any time of life, such as myasthenia gravis. Toxins such as alcohol can also affect muscle tissue, as well as abnormalities of hormonal production.
The diagnosis of the cause of neuromuscular paralysis is made by careful evaluation of the nervous system, and the use of ancillary tests.