Primary lateral sclerosis (PLS) is a rare neuromuscular disease that affects the nerve cells that control the voluntary muscles. Problems in the legs (such as weakness, stiffness, spasticity, and balance problems) are often observed first, but hand clumsiness and changes in speech can be early symptoms, as well. The condition is progressive (gradually becomes worse over time); however, affected people have a normal life expectancy. The underlying cause of adult PLS is currently unknown. In most cases, it occurs sporadically in people with no family history of the condition. A subtype of PLS, called juvenile PLS, is caused by changes (mutations) in the ALS2 gene and is inherited in an autosomal recessive manner. Treatment is based on the signs and symptoms present in each person.

The signs and symptoms of primary lateral sclerosis (PLS) often develop between the ages of 40 and 60 and progress (become worse) over time. The voluntary muscles of the legs are often involved first, with symptoms beginning in one leg and then progressing to the other. In general, people with PLS may experience:

• Muscle weakness
• Muscle stiffness and spasticity
• Difficulty with balance and clumsiness
• Slowed movement
• Problems with speech

The treatment of primary lateral sclerosis (PLS) is based on the signs and symptoms present in each person. For example, certain medications may be prescribed to treat the muscle stiffness and/or pain that can be associated with the condition. Physical therapy and occupational therapy can help maintain muscle strength, flexibility and range of motion, and may prevent joint immobility. Assistive devices such as braces, canes, walkers or wheelchairs may be needed for continued mobility. Speech therapy may be recommended when facial muscles are involved.

A diagnosis of primary lateral sclerosis (PLS) may be suspected based on the presence of characteristic signs and symptoms. Several different medical tests may then be ordered to confirm the diagnosis and rule out other conditions (such as multiple sclerosis and amyotrophic lateral sclerosis) that can be associated with similar features. These tests may include:

• Blood work
• Magnetic resonance imaging (MRI) of the brain and spine
• Motor and sensory nerve conduction studies
• Electromyogram (EMG)
• Cerebrospinal fluid (CSF) analysis

Although a preliminary diagnosis of PLS can be made after other conditions are ruled out, it may take repeated testing over three to four years to confirm the diagnosis.