Primary lateral sclerosis (PLS) is a rare neuromuscular disease characterized by progressive muscle weakness in the voluntary muscles. PLS belongs to a group of disorders known as motor neuron diseases. Motor neuron diseases develop when the nerve cells that control voluntary muscle movement degenerate and die, causing weakness in the muscles they control.
Onset of PLS usually occurs after age 50. Symptoms may include difficulty with balance, weakness and stiffness in the legs, and clumsiness. Other symptoms may include spasticity (sudden, involuntary muscle spasms) in the hands, feet, or legs; foot dragging, and speech problems due to involvement of the facial muscles. The disorder usually begins in the legs, but it may also start in the tongue or the hands.
The disease -- which scientists believe is not hereditary -- progresses gradually over a number of years, or even decades. In PLS, there is no evidence of the degeneration of spinal motor neurons or muscle wasting (amyotrophy) that occurs in amyotrophic lateral sclerosis.
The issue of whether PLS exists as a different entity from ALS is not clear as some patients initially diagnosed as having PLS ultimately develop lower motor neuron signs.
Treatment for individuals with PLS is symptomatic. Baclofen and tizanidine may reduce spasticity. Quinine or phenytoin may decrease cramps. Physical therapy often helps prevent joint immobility. Speech therapy may be useful for those with involvement of the facial muscles.
Patients can often live with PLS for many years and very often outlive their neurological disease and succumb to some unrelated condition. There is currently no effective 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.
^ Tartaglia MC, Rowe A, Findlater K, Orange JB, Grace G, Strong MJ (2007). "Differentiation between primary lateral sclerosis and amyotrophic lateral sclerosis: examination of symptoms and signs at disease onset and during follow-up". Arch. Neurol.64 (2): 232–6. doi:10.1001/archneur.64.2.232. PMID 17296839.
^ Gotkine M, Argov Z (2007). "Clinical differentiation between primary lateral sclerosis and upper motor neuron predominant amyotrophic lateral sclerosis". Arch. Neurol.64 (10): 1545; author reply 1545. doi:10.1001/archneur.64.10.1545-a. PMID 17923644.