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Amyotrophic lateral sclerosis (ALS) is an acquired, progressive, degenerative motor neuron disease. ALS, also known as Lou Gehrig's disease, accounts for approximately 80% to 90% of all acquired1 motor neuron diseases in adults, with the remaining 10% to 20% representing only lower motor signs or a familial form of ALS (Dal Bellow-Haas, Kloos & Mitsumoto, 1998; Goldman & Bennett, 2000).
ALS affects both upper and lower motor neurons. The motor neurons in the spinal cord, brain stem, and cerebral motor cortex degenerate, resulting in a variety of signs and symptoms. The disease is characterized by the absence of sensory symptoms and findings.
Seventy percent of patients present initially with leg, arm, or bulbar (muscles used for swallowing) muscle focal weakness. Lower-extremity motor neuron clinical signs include muscle weakness, muscle atrophy, fasciculations (muscle twitches), hyperreflexia, hypotonicity, and muscle cramps. Upper-extremity motor neuron clinical signs include spasticity, hyperreflexia, and pathological reflexes. Bulbar signs include dysarthria2, dysphagia (difficulty swallowing), sialorrhea (drooling), and pseudobulbar palsy (Dal Bellow-Haas et al., 1998). Cognition, extra-ocular eye movements, and autonomic, bowel, bladder, and sexual functions usually remain intact (Dal Bellow-Haas et al., 1998, Goldman & Bennett, 2000).
To definitely diagnose ALS, the body is divided into four regions:
1) bulbar - jaw, face, palate, larynx, and tongue;
2) cervical - neck, arm, hand, and diaphragm;
3) thoracic - back and abdomen; and
4) lumbosacral - back, abdomen, leg, and foot (Goldman & Bennett, 2000).
A definite diagnosis is made when upper and lower motor neuron signs are present in the bulbar region and two other spinal regions, or in three spinal regions. Individuals with motor neuron signs in only two spinal regions are classified as having probable ALS. Possible ALS is the diagnosis if dysfunction is present in only one region, or if a patient presents with only upper motor neuron signs in two regions, or if lower motor neuron signs are found in the upper-extremity muscles (Goldman & Bennett, 2000).
Muscle weakness progresses over time; the pattern and rate of deterioration varies widely. ALS has an incidence rate of two to four people in 100,000 (Goldman & Bennett, 2000). It is slightly more common in men than women, with the average age of onset in the mid-50s (Dal Bellow-Haas et al., 1998). The duration of the disease, from onset of symptoms until death, is 27 to 43 months; the average 5-year survival rate is 25% (Goldman & Bennett, 2000). However, about 10 percent of ALS patients survive for 10 or more years. Death is usually due to respiratory failure.
The cause of sporadic ALS is unknown. In a case study by Dal Bellow-Haas et al. (1998), a breakthrough in ALS research found that the disease may be caused by a mutation in the superoxide dismutase-1 (SOD1) gene. This would confirm studies by Bredesen, Ellerby, Hart, Wiedau-Pazos, and Valentine (1997); Bowling, Schulz, Brown, and Beal (1993); and Kawamata, J., Shimohama, S., Takano, S., Harada, K., Ueda, K., & Kimura, J. (1997) that suggest that ALS is caused by free-radical injury.
Another possible cause is an accumulation of neurofilaments (proteins that serve as supporting structures in neurons) found in motor neuron axons. Other researchers have found that glutamate, an excitatory neurotransmitter, were elevated in CSF fluid, and that glutamate uptake was decreased in brain tissues of people with ALS (Dal Bellow-Haas et al., 1998). The overstimulation of nerve cells by excessive levels of glutamate may lead to cell death. Compromise of the immune system may also be a cause of ALS. The serum of people with ALS has been shown to contain antibodies to motor neurons, according to a study by Appel, Stockton-Appel, Stewart, and Kerman (cited in Dal Bellow-Haas et al., 1998).
In a study by Armon, Kurland, Daube, & O'Brien (1991), risk factors for ALS were investigated. Exogenous or endogenous causes, or a combination thereof, were being examined to determine the chain of events in the development of ALS. The study investigated these five factors:
- athletic prowess/hard physical labor,
- family history of neurodegenerative disease,
- exposure to lead,
- years lived in a rural community, and
- past trauma or major surgery.
There was no association that could be drawn between those five factors and the development of ALS.
Kurland, Radhakrishnan, Smith, Armon, & Nemetz (1992) conducted a literature review regarding the role of trauma in the development of ALS. They hypothesize the following roles of trauma:
- Causes ALS in a subgroup of the population;
- Predisposes to the subsequent development of ALS;
- Promotes a sub-clinical disease process;
- Precipitates the clinical manifestation of ALS; and
- Coincidental to and wholly independent of ALS.
The study concluded that the relationship is unproven for at least three reasons: the major methodological shortcomings of studies reporting a significant relationship; the absence of a plausible biological theory to account for a relationship between trauma and the pathogenesis of ALS; and the lack of an animal model.
A pilot study by Strickland, Smith, Dolliff, Goldman, & Roelofs (1996) explored the possibility of physical trauma and physical activity leading to the development of ALS. The study reported a positive association between severe head, neck, and back trauma and bone fractures. It also found that these events were reported at a younger age in people with ALS. The authors argue that ALS is a disease of the anterior horn cells of the spinal cord, and that focal trauma could have an effect that might begin or accelerate anterior horn cell degeneration (Strickland et al., 1996). They also say that further investigation needs to be done to determine if such associations exist.
Currently, there is no cure for ALS. There are medications that have beneficial effects. Available by prescription is Riluzol (Rilutec), which inhibits glutamate release and antagonizes the glutamate receptor; it prolongs survival (Dal Bellow-Haas et al., 1998). Another drug is Myotrophin (insulin-like growth factor-I [IGF-I]), which moderately lessens motor dysfunction (Dal Bellow-Haas et al., 1998). It promotes the survival of motor neurons and regeneration of motor nerves. (Myotrophin has been approved by the U.S. Food and Drug Administration as an investigational new drug.)