Motor neuron diseases are progressive disorders that affect the neurological system by destroying cells called motor neurons. These cells are responsible for controlling voluntary muscle actions. People with motor neuron diseases have difficulty controlling actions such as walking, breathing, swallowing and speaking. There are several types of motor neuron disease, including primary lateral sclerosis, spinal muscular atrophy and amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease. The terms "motor neuron disease" and "amyotrophic lateral sclerosis" are often used interchangeably, particularly in the United States and Canada.
Motor neuron diseases occur in children as well as adults and can occur in both sexes, although they are more common in men. This is because some types of motor neuron disease are X-linked, which means the gene causing the disease is located on the X chromosome. A woman can inherit one defective copy of the gene without developing the disease, because she has two X chromosomes and therefore also has a normal copy of the gene. In contrast, if a man inherits a defective copy of the gene, there is no second X chromosome to provide a normal copy.
In classic ALS, the first motor neuron disease symptoms to appear usually are related to the function of hands, arms or legs. Muscle weakness and wasting are common initial symptoms. In addition, individuals might have difficulty swallowing. As the disease progresses, muscles become increasingly weaker, and more muscle groups are affected. In addition to difficulty swallowing, it is common for an individual to begin having difficulty speaking and breathing, because of weakness and wastage of the diaphragm and chest muscles. It is rare for motor neuron diseases to impair cognitive function.
Other types of motor neuron disease cause slightly different symptoms. In primary lateral sclerosis, for example, the legs, arms and hands are most affected, and individuals have problems with balance, muscle stiffness and weakness. In spinal muscular atrophy, muscle weakness and atrophy is most severe in the legs, and individuals do not always experience loss of breathing, speaking or swallowing control.
Motor neuron diseases cannot be cured, and there are no standard treatment protocols for these diseases. In most cases, motor neuron disease treatment includes physical therapy, medications to treat symptoms and other supportive treatments. For example, medications to relieve pain, relax muscles and relieve inflammation are often prescribed. Physical therapy is used to preserve muscle tone, strength and flexibility and to slow the pace of muscle degeneration. Occupational therapy and devices such as a wheelchair or speech synthesizer help the individual retain as much independence as possible.