Primary Lateral Sclerosis - a rare neuromuscular disease characterised by progressive
muscle weakness in the voluntary muscles. PLS belongs to a group of disorders known
as the 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.
PLS affects upper motor neurons only. 1 The disease occurs from 40 yrs onwards and
usually begins in the legs, but it may also start in the tongue or the hands.
Symptoms may include:
Difficulty with balance.
Weakness and stiffness in the legs.
Clumsiness.
Spasticity - involuntary, sustained contraction that is resistant to initial passive
movement in the hands, feet, or legs.
Foot dragging.
Speech problems due to affected facial muscles.
The disease will progress gradually over a number of years, and sometimes decades.
However, there is no sign of the degeneration of spinal motor neurons or muscle wasting
(amyotrophy) such as that which occurs in amyotrophic lateral sclerosis (ALS).
The issue of whether PLS exists as a different entity from ALS is not clear as some
people initially diagnosed as having PLS ultimately develop lower motor neuron signs.
The diagnosis of PLS requires extensive testing to exclude other diseases. When symptoms
begin, PLS may be mistaken for amyotrophic lateral sclerosis and the diagnosis for
PLS can be delayed for several years.
Upper motor neurons control voluntary movement. The cell bodies of these neurons
are located in the motor cortex area of the brain. Their axons travel to the brainstem
and down the spinal cord which relay the message impulse to move down to the lower
motor neurons located along the brainstem and spinal cord. Lower motor neurons then
relay the message impulse out to the muscles.
When upper motor neurons degenerate, message impulses cannot adequately reach the
lower motor neurons. Therefore, the lower motor neurons will not relay the proper
message impulse to the corresponding muscle.
The result is muscle weakness and spasticity. As the degeneration progresses, symptoms
increase.
The rate at which symptoms progress and how severe they become is impossible to predict.
An individual's genes, environment, nutrition, general health, and other factors
may influence the rate of progression and severity of the disease.
