The Spastic Paraplegia Foundation is dedicated to advancing research and finding cures for two groups of closely related, rare, and progressive neurological disorders. They are Hereditary Spastic Paraplegia (HSP) and Primary Lateral Sclerosis (PLS). These are neurological disorders affecting the voluntary muscles. The disorders are progressive and may lead to patients being unable to walk, and more.

Hereditary Spastic Paraplegia (HSP) is a group of rare, inherited neurological disorders. Their primary symptoms are progressive spasticity and weakness of the leg and hip muscles. Researchers estimate that some 90 different types of HSP exist; the genetic causes are known for about fifty. The HSP incidence rate in the United States is about 20,000 people. The condition is characterized by insidiously progressive lower extremity weakness and spasticity. HSP is classified as uncomplicated or pure if neurological impairment is limited to the lower body. HSP is classified as complicated or complex if other systems are involved or if there are other neurological findings such as seizures, dementia, amyotrophy, extrapyramidal disturbance, or peripheral neuropathy in the absence of other disorders such as diabetes mellitus. Many different names are used for HSP. The most common are Hereditary Spastic Paraplegia (or Paraparesis), Familial Spastic Paraparesis (or Paraplegia), and Strümpell-Lorrain Disease. Others are Spastic Paraplegia, Hereditary Charcot-Disease, Spastic Spinal Paralysis, Diplegia Spinalis Progressive, French Settlement Disease, Troyer syndrome, and Silver syndrome. The disorder was first identified in the late 1800s by A. Strümpell, a neurologist in Heidelberg, Germany. He observed two brothers and their father, all of whom had gait disorders and spasticity in their legs. After the death of the brothers, Strümpell showed through autopsy the degeneration of the nerve fibers leading through the spinal cord. HSP was originally named after Strümpell, and later after two Frenchmen, Lorrain and Charcot, who provided more information.

Primary Lateral Sclerosis (PLS) is a group of rare, degenerative, neurological disorders. They are sporadic, meaning there is no clear familial link, although there are hereditary forms of PLS. PLS is caused primarily by degeneration of the upper motor neurons in the brain and spinal cord, which results in increasing spasticity and weakness of voluntary muscles. It is often referred to as a benign variant of Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig’s disease). The primary difference between the two is that in PLS the spinal motor neurons or lower motor neurons stay intact. Thus, there is no muscle wasting (amyotrophy), which is the symptom that ultimately causes fatal complications in ALS.

The disorder usually begins in the legs but can begin in the upper body or bulbar (speech and swallowing) muscles. The age of onset is generally between 35 and 66 years of age, with a median age of 50. The incidence rate for PLS is difficult to determine. One study puts it at 500 individuals in the United States. However, many researchers feel this is inaccurate, and that the actual incidence rate is closer to 2000. The issue is further complicated by the fact that researchers also believe a good portion of those initially diagnosed with PLS may have ALS or HSP.

PLS was first identified in France in the 1850s by Dr. Jean-Martin Charcot. During his landmark analyses of ALS patients, Dr. Charcot encountered a woman with severe spasticity and limb contractures but no muscle wasting. After she died in 1856, the autopsy revealed extensive scarring in the lateral columns of her spinal columns or primary lateral sclerosis.