What
is amyotrophic lateral sclerosis (ALS)?
ALS
is a progressive, degenerative disease of the nervous system.
It is one of a group of diseases, called motor neuron diseases
(MND), in which specialized nerve cells that control movement
of the voluntary muscles gradually cease functioning and die.
These nerve cells, called motor neurons, carry impulses from
the brain to the brainstem and the spinal cord. The impulses
are then carried to the muscles. The muscles respond to these
messages by coordinated relaxation or contraction corresponding
to willed movement. In ALS and other motor neuron diseases,
motor neurons gradually deteriorate. Because the nerve cells
that stimulate them have died, the muscle tissues waste away.
This results in progressive muscle weakness, atrophy, and
often spasticity, or excess muscle tone. Only the motor neurons
are affected. Other nerve cells, such as sensory neurons that
bring information from sense organs to the brain, remain healthy.
Are
there other names for ALS?
ALS,
also known as motor neuron disease (MND), is commonly called
Lou Gehrig's disease for the famous New York Yankee's baseball
player who died of ALS in 1941. ALS is sometimes referred
to as Charcot's disease for the French neurologist Jean-Martin
Charcot who identified the disease in 1869.
Who
gets ALS?
Most
who develop ALS are between 40 and 70 years of age, although
the disease can strike at any age. Men are affected slightly
more frequently than women. ALS occurs throughout the world
regardless of racial, ethnic or socioeconomic status.
Some
studies have identified areas that at certain times have appeared
to have greater than expected numbers of cases. This has occurred
in the past in the western Pacific islands and in parts of
Japan and Australia. Other areas in the continental United
States have been reported but have not stood up to careful
epidemiological investigations.
How
common is ALS?
More
than 5,600 Americans are diagnosed with ALS each year or two
new ALS cases per 100,000 people (incidence). Approximately
35,000 people at any given time are living with ALS in the
United States or six to eight people per 100,000 population
(prevalence). The incidence of ALS is close to that of multiple
sclerosis and four times that of muscular dystrophy.
What
are the symptoms of ALS?
ALS
strikes people in different ways and progression of the disease
is often irregular. Some of the early symptoms of ALS are:
- Weakness
or difficulty in coordination in one limb
- Changes
in speaking or swallowing
- Unusual muscle twitches, spasms, or cramps
- Unusual weight loss or loss of muscle bulk
The
symptoms and clinical features of the disease depend on the
location of the affected motor neurons. Speech and swallowing
impairments are called bulbar symptoms. They indicate that
neurons in the brainstem are affected. Weakness of the respiratory
muscles, muscle weakness, and loss of mobility in the arms
and legs are called somatic symptoms. They indicate spinal
cord involvement. In classical ALS, a mixture of upper and
lower motor neurons are involved, with both bulbar and somatic
symptoms.
-
Lower
motor neuron symptoms
Weakness and muscle wasting are common when lower motor
neuron involvement predominates. The patient or physician
usually notices fasciculation, or muscle twitching. Fasciculation
is a sign of muscle irritability, as the normal action
of the lower motor neuron on the muscle is impaired. The
sole involvement of lower motor neurons can be seen in
a form of ALS called progressive muscular atrophy. Fasciculation
is described as "benign" if there is no muscle
weakness, atrophy, or impairment of motor function. Fasciculation
is described as "pathologic" when it occurs
in ALS with other symptoms.
-
Upper
motor neuron symptoms
Spasticity, or stiffness, in the lower limbs, face, or
jaw indicates upper motor neuron involvement. Spasticity
in the legs often produces severe walking difficulties.
The patient may complain of heaviness, fatigue, stiffness,
or lack of coordination of any affected limb. Reflexes
are very brisk, or exaggerated. Outbursts of laughter
or crying with minimal provocation can occur. This is
called emotional lability and is referred to as a pseudo-bulbar
affect. Both brisk reflexes and emotional lability involve
the inability to inhibit reflexes.
The
diagnosis of ALS is a "clinical diagnosis," meaning
there is no specific test that gives a definitive answer.
Before a diagnosis of ALS is confirmed, many tests must be
administered to rule out illnesses with symptoms that may
mimic ALS. These may include an MRI of the brain or spinal
cord, an electromyography (EMG) study of nerve and muscle
function and a variety of blood and urine tests. By evaluating
these tests, the patient's medical history and performing
a complete neurological exam, the neurologist can usually
reach a definitive diagnosis.
It
is always recommended that patients seek a second opinion
by a neurologist experienced with ALS in order to decrease
the possibility of an incorrect diagnosis. In some cases a
definitive diagnosis can be made only after several months
of observation and retesting.
What
is the prognosis of ALS?
ALS
progresses at different rates in each individual. The average
survival for someone affected by ALS is three to five years.
A small percentage of people have a very slow progression
and live 10-20 years with the illness at various levels of
disability. Weakness of the bulbar and somatic muscles produces
a decline in speech, swallowing, and limb strength and function.
The ALS patient usually remains alert throughout the course
of the illness and retains normal sensation, vision, and bowel
function. Bladder function is impaired in 1% of patients.
Generally, ALS is not a physically painful condition. Discomfort
can result from immobility and joint contractures, a shortening
of muscles resulting in deformity. While most patients do
not have loss of intellectual function, some may have subtle
changes in mood, behavior, or personality. In a small minority
of patients, more significant changes in behavior and judgment
suggest a form of dementia.
Each
ALS patient is unique in regard to the rate and characteristics
of the progression of the disease. Although the clinical progression
can vary greatly, 50 percent of those diagnosed will succumb
to the illness within five years of the onset of symptoms
What
causes ALS?
It
is likely that there are several different causes of ALS.
Two genes have been identified that cause familial ALS. The
causes of sporadic forms of ALS are still unknown.
One
hypothesis is that a group of gene mutations inherited together
predispose one to ALS such that a threshold is formed. Environmental
factors may "push" someone over the threshold so
that ALS symptoms occur. Both the predisposing genes and environmental
factors are unknown at this time.
Is
there any treatment for ALS?
Many
of the symptoms of ALS are treatable, but there are no drugs
available to cure the disease. Rilutek©, the first FDA-approved
medication for the treatment of ALS, has been shown to modestly
increase lifespan. Since it became available in 1996, two
retrospective studies presented at the 12th International
Symposium on ALS/MND in 2001 indicated that Rilutek©
appears to have a greater impact on life expectancy than was
reported in initial drug trials.
The
quality of life of patients with ALS can often be improved
by various treatments and interventions. Proper positioning,
exercise, physiotherapy, and medications can help keep patients
comfortable. Patients with significant bulbar involvement
may require help to improve communication or ensure safe and
adequate nutrition. A gastrostomy (feeding) tube may be suggested
if there is recurrent pneumonia, high risk of aspiration (inhaling
food or liquids into the lungs), inadequate nutrition, rapid
weight loss, or extended feeding time. A wide range of devices
and techniques can address problems with communication. Ultimately,
ALS may result in respiratory decline, requiring consideration
of respiratory support, including non-invasive ventilation
such as a BiPAP (bilevel positive airway pressure), or a tracheotomy
and a ventilator.
Is
ALS inherited?
Familial
(genetic) ALS accounts for 10% of all ALS cases. ALS is considered
familial if there are two or more cases within the same bloodline.
If no family history exists, the disease is termed sporadic
and other family members are not thought to be at increased
risk for developing the disease.
Are
there diseases similar to ALS?
Although
it is the most serious, ALS is one of a number of diseases
affecting the nerve cell, or motor neuron. Some involve only
upper motor neurons, which run from the motor cortex of the
brain to the brain stem and/or spinal cord. Others involve
lower motor neurons, which run from the brain stem and spinal
cord to muscles.
-
Spinal
muscular atrophy (SMA)
SMA variations include childhood forms and a less frequent
adult form, which involves only the lower motor neurons.
Inheritance of adult SMA is autosomal recessive. Symptoms
are generalized weakness and muscle wasting with muscle
twitching. Onset is over 18 years into adulthood with
variable progression and normal life expectancy.
-
Primary
lateral sclerosis (PLS)
PLS, a degenerative disease of the upper motor neurons
only, has symptoms of progressive spasticity, difficulty
in walking, and pseudobulbar affect. PLS affects the trunk,
extremities and bulbar muscles. PLS is not considered
to shorten life expectancy as it has a slow progression
over the course of approximately 20 years. Because ALS
may initially present with signs of only upper motor neuron
involvement, a diagnosis of PLS has the potential to be
reclassified as ALS if sufficient signs of upper and lower
motor neuron involvement are present.
-
Spinal
bulbar muscular atrophy (Kennedy's Disease)
Symptoms are weakness and muscle wasting of the bulbar
muscles (throat and mouth) and skeletal muscles. Facial
and muscle jumping is common; breast development, infertility
and testicular wasting can occur. It usually affects only
men. Females are carriers who are usually asymptomatic
or have a mild form. Onset is adulthood with progression
being slow and variable with normal lifespan. Inheritance
is X-linked recessive.
(Back
to Top)
|
