Primary lateral sclerosis (PLS) is an ALS-related disease, with different symptoms than ALS. It is a progressive disorder of the central motor neurons of which the cause is unknown and for which there is no treatment.
It is a nerve/muscle disease in which the motor nerve cells deteriorate. This leads to stiffness and spasticity of the muscles in the legs and sometimes the arms. Speech and swallowing disorders also occur. It is estimated that more than 100 people in the Netherlands have this disease.
In PLS, there is a problem with the central motor neurons. This is due to a hardening (sclerosis) of the tissue that is located on the sides (lateral) of the spinal cord. The symptoms usually occur after the age of 30. PLS does not have to shorten lifespan, but it often leads to disability.
PLS has a much slower progression than ALS. People suffer from stiffness and increased muscle tone with increased reflexes. This usually starts in both legs, causing people to stumble, have difficulty running, and have less strength. Later, muscle weakness also develops in the hands and arms. Over time, chewing, swallowing and speech problems can arise. A definitive diagnosis of PLS can only be made after 4 years. Within 4 years there is a chance that the disease will progress to ALS.
Source: ALS Netherlands Foundation