Primary lateral sclerosis (PLS) is a rare neuromuscular disease with slowly progressive weakness in voluntary muscle movement.

PLS belongs to a group of disorders known as motor neuron diseases. In motor neuron diseases, the nerve cells that control voluntary muscle movement degenerate and die. In PLS, the corticospinal motor neurons (often called “upper motor neurons”) in the brain are affected. There is no evidence of degeneration of lower motor neurons in the spinal cord or brainstem and there is little muscle wasting (amyotrophy).

Onset of PLS usually occurs after age 40. Scientists do not believe PLS has a simple hereditary cause. There are similar, but rare, hereditary childhood disorders termed “juvenile PLS.”

Symptoms include:

• Weakness
• Muscle stiffness
• Muscle spasms (spasticity)
• Clumsiness
• Slowing of movement
• Problems with balance

The symptoms often begin with problems in the legs, but may also start with hand clumsiness or changes in speech. PLS progresses gradually over a number of years, or even decades.

The diagnosis of PLS requires extensive testing to exclude other diseases. When symptoms begin, PLS may be mistaken for amyotrophic lateral sclerosis or ALS (Lou Gehrig’s disease) and the diagnosis of PLS can be delayed for several years.

PLS is not fatal. There is no cure and the progression of symptoms varies. Some people may retain the ability to walk without assistance, but others eventually require wheelchairs, canes, or other assistive devices.

Treatment for individuals with PLS is symptomatic. Medications such as baclofen and tizanidine may reduce spasticity. Quinine or phenytoin may decrease cramps. Physical therapy helps prevent joint immobility and maintain muscle strength. Speech therapy may be useful for those with involvement of the facial muscles.