The Spastic Paraplegia Foundation is dedicated to advancing research and finding the cures for two groups of closely related, progressive neurological disorders: Primary Lateral Sclerosis (PLS) and Hereditary Spastic Paraplegia (HSP).  PLS is generally a sporadic condition, with unknown cause. HSP is a genetic condition, caused by an inherited, defective gene. Please see HSP-Heredity.

In both groups of diseases, nerves involved in voluntary movement degenerate. These "upper motor" nerves begin in the motor cortex of the brain and extend down the spinal cord. Their job is to carry signals from the brain to the "lower motor" neurons, which begin in the spinal cord. The lower motor neurons relay messages out to the muscles, telling them to contract or relax.

Because the upper motor neurons are degenerating, they do not give the correct signals to the lower motor neurons. Thus, the muscles do not receive the correct messages. This causes spasticity and weakness of the affected muscles. As the nerves continue to degenerate, the spasticity and weakness in the muscles increase.

Read What's Happening and click the thumbnail diagram at the right.

In most forms of HSP, the condition primarily affects the lower body. However, rare forms of the disease can also have upper body or additional neurological symptoms. In PLS, the arms, speech and swallowing are generally affected as well. Symptoms typically start in the lower body, although they can begin in the upper body, first.

HSP and PLS can be referred to as "primary upper motor neuron disorders" because there is little, if any, lower motor neuron disease, which distinguishes HSP and PLS from ALS.

The disorder name "Hereditary Spastic Paraplegia" describes the symptoms of the disease. HSP is Heredity and it's symptoms are Spasticity and Paraplegia. The term "Primary Lateral Sclerosis" describes the disease process, rather than the symptoms. Degeneration occurs: Primarily in the Lateral columns of the spinal cord. Sclerosis means "scarring".

Since HSP and PLS share the same symptoms in the lower body, it is often unclear which is the correct diagnosis. Often, the true diagnosis is discovered over time as symptoms further develop. Overview Summary Chart