Diseases of the upper motor neurons
Diseases of the upper motor neurons affect neurons of the motor cortex - nerve cells in the brain. Upper motor neurons direct the lower motor neurons to produce movements such as walking or chewing.
Diseases include Primary lateral sclerosis PLS and Pseudobulbar palsy both described below.
"Involvement of upper motor neurons
results in stiffness of muscles (spasticity) and slowed movements,
sometimes the muscles will spasm or spontaneously jerk." MND Fact Sheets Australia
Primary lateral sclerosis PLS affects only upper motor neurons and is nearly twice as common in men as in women. Onset generally occurs after age 50.
The cause of PLS is unknown. It occurs when specific
nerve cells in the cerebral cortex (the thin layer of cells covering the
brain which is responsible for most higher level mental functions) that
control voluntary movement gradually degenerate, causing the muscles
under their control to weaken. The syndrome -- which scientists believe
is only rarely hereditary -- progresses gradually over years or
decades, leading to stiffness and clumsiness of the affected muscles.
The disorder usually affects the legs first, followed by the body trunk,
arms and hands, and, finally, the bulbar muscles. Symptoms may include
difficulty with balance, weakness and stiffness in the legs,
clumsiness, spasticity in the legs which produces slowness and stiffness
of movement, dragging of the feet (leading to an inability to walk),
and facial involvement resulting in dysarthria (poorly articulated speech).
Major differences between ALS and PLS (considered a
variant of ALS) are the motor neurons involved and the rate of disease
progression. PLS may be mistaken for spastic paraplegia, a hereditary
disorder of the upper motor neurons that causes spasticity in the legs
and usually starts in adolescence. Most neurologists follow the
affected individual's clinical course for at least 3 years before making
a diagnosis of PLS. The disorder is not fatal but may affect quality
of life. PLS often develops into ALS
Pseudobulbar palsy,
which shares many symptoms of progressive bulbar palsy, is
characterized by upper motor neuron degeneration and progressive loss of
the ability to speak, chew, and swallow. Progressive weakness in
facial muscles leads to an expressionless face. Patients may develop a
gravelly voice and an increased gag reflex. The tongue may become
immobile and unable to protrude from the mouth. Patients may also
experience emotional lability
