Primary lateral sclerosis

Primary lateral sclerosis (PLS) is a rare, slowly progressive, neurological disorder of unknown cause. It leads to degeneration of nerve cells (motor neurons) in certain areas of the brain that control voluntary muscles. This results in:

• Muscle weakness
• Muscle cramps
• Sudden, involuntary muscle spasms
• Stiffness (spasticity)

Symptoms of primary lateral sclerosis often begin in the legs and gradually progress to the back, arms and face. As the disease worsens over many years, it can lead to balance problems and falls. It can also be associated with pain.

Because primary lateral sclerosis resembles amyotrophic lateral sclerosis (ALS), it is sometimes misdiagnosed as ALS. But unlike ALS, primary lateral sclerosis affects only the upper motor neurons in the brain and not the lower motor neurons in the spinal cord — so it doesn't cause the muscle wasting (atrophy) seen in ALS. Also, primary lateral sclerosis isn't fatal.

A doctor may make a diagnosis of primary lateral sclerosis based on:

• Signs and symptoms
• Medical history
• Neurological exam
• Magnetic resonance imaging (MRI) scan
• Electromyography (EMG) studies

There is no specific treatment for primary lateral sclerosis. Treatment is usually directed at managing the signs and symptoms and may include:

• Physical therapy
• Medications, such as baclofen (Lioresal) and tizanidine (Zanaflex), to treat spasticity