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Genetic and Rare Diseases Information Center (GARD)

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Primary lateral sclerosis

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What are the signs and symptoms of primary lateral sclerosis?

Primary lateral sclerosis (PLS) causes weakness in the voluntary muscles, such as those used to control the legs, arms and tongue. PLS can happen at any age, but it is more common after age 40. A subtype of PLS, known as juvenile primary lateral sclerosis, begins in early childhood. PLS is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). However, primary lateral sclerosis progresses more slowly than ALS, and in most cases is not considered fatal.[1]

Signs and symptoms of PLS typically take years to progress.[1] The hallmark of PLS is progressive weakness and spasticity of voluntary muscles. The first symptoms are often tripping or difficulty lifting the legs. Other people may be the first to notice a change in the affected person's gait. Occasionally, speaking (dysarthria) and swallowing (dysphasia) difficulties, or arm weakness are the first symptoms. Speech problems can begin with hoarseness, a reduced rate of speaking, excessive clearing of the throat, or slurred speech when a person is tired. In some cases, speech becomes so slurred that others cannot understand it. Drooling can be a problem as well due to weakened bulbar muscles.[2] Many people report painful muscle spasms and other pain. Other common symptoms may include hyperactive reflexes and Babinkski's sign. Wherever symptoms originate, the legs, arms, hands, and speech and swallowing muscles are eventually affected. As the disease progresses, assistive devices such as canes, walkers or wheelchairs are typically needed.[2]
Last updated: 3/30/2011

  1. Primary lateral sclerosis (PLS). Mayo Clinic. October 16, 2010; Accessed 3/30/2011.
  2. John Fink. About PLS (Primary Lateral Sclerosis). Spastic Paraplegia Foundation. 2011; Accessed 3/30/2011.