The second cell type called "the lower motor neuron" starts in the spinal cord and sends fibers out to muscles. When a lower motor neuron degenerates, the muscle fibers it normally activates become disconnected and do not contract, causing muscle weakness and diminished reflexes. Although the affected nerve cells cannot grow back, the remaining healthy lower motor neuron fibers may send out nerve branches in the muscle and reinnervate or reconnect to the muscle fibers. This occurs to a limited degree and slows the progression of weakness. Loss of either type of neuron results in weakness, and painless weakness is the major symptom of motor neuron disease.
Motor neuron disease is a syndrome. The term "syndrome" means that patients with the disease can show a variety of patterns of involvement, but the overall features allow for proper diagnosis. At the time of diagnosis, weakness may be noted in muscles of a single limb or several limbs, or muscles of speech and swallowing may be involved. At later times, weakness may effect speech, swallowing, or breathing. The time-course is variable, and no two people follow the same pattern of involvement or rate of progression.
The diagnosis of motor neuron disease is made from a careful history, a physical examination, and an EMG study. There is no single test available which gives a "yes" or "no" answer. It is the pattern of findings and exclusions of other diseases which allows the neurologist to establish a diagnosis and to determine which form of the syndrome is present. Blood studies, imaging (CT, MRI), and EMG studies help to exclude other diagnoses.
The incidence of motor neuron disease is approximately 2 cases per 100,000 people. In the majority of cases no cause is identified and the term "sporadic motor neuron disease" is used. From investigations we know that common life events, experiences, and habits are not associated with it. Specific foods or vitamins have not been associated with it. Traumatic injury or surgery is not a known factor. For a very few individuals (5-10%), motor neuron disease is hereditary and almost always the patient and family know of direct blood relatives with the syndrome. There exists an even smaller group of patients in whom a specific genetic mutation is found for a type of inherited ALS. Much of the history and many of the laboratory tests that are conducted during the initial diagnostic period are used to identify this group of patients.
Many names have been applied to the syndrome of motor neuron disease. Among those frequently used are Amyotrophic Lateral Sclerosis (ALS) and Lou Gehrig's Disease. ALS is the most common form of motor neuron disease in adults. There are rare forms such as Primary Lateral Sclerosis (affecting upper motor neurons only) and Spinal Muscular Atrophy (affecting lower motor neurons only). The term Lou Gehrig's Disease describes the course in a single individual and does not accurately reflect the course in other people.
The varied features of motor neuron disease mean that the course or prognosis is also varied. No one can predict the future of a medical condition with certainty. How fast an individual patient will develop new weakness can best be estimated by looking back at how fast strength has been lost. Because reinnervation helps to maintain strength, most patients have had motor neuron disease for a longer period than they realize. This means that for many individuals changes take place slowly, sometimes over years, and progression may be punctuated by periods of apparent stability.
Weakness is the major symptom in motor neuron disease. Thinking and memory are unaffected. Vision, hearing, and sensation remain normal. Full control of bowel and bladder function is retained, although there may be urinary urgency. Sexual potency also is unaffected. Pain is not typical. Some people may have muscle cramps which may be briefly uncomfortable and for which medication is given. Occasionally there is pain in or about joints which is due to weak muscles (muscle imbalance). This often can be improved by physical therapy and bracing.
At this time there is no cure for motor neuron disease. There is currently only one medication available by prescription (Rilutek) which has been shown in clinical trials to slow the progress of ALS a small amount. Over the past 10 years it appears that people with ALS are living longer because of improved care and increased knowledge of the disease.
There are many articles in the press and on the Internet about new medications and home cures which may be passed on by friends. There are many physicians and scientists carrying out research on this and related disorders and conducting clinical trials of medications in hospitals across the country and around the world. The Motor Neuron Disease Center actively follows research on this disease as well as conducting our own research. We are, therefore, in a position to offer information as it becomes available and to answer questions.
Regular neurologic and physical evaluations are useful to assess changes, answer questions, and address needs of the work place and home. Neurologists and nurse practitioners work closely with physical therapists, occupational therapists, social workers, speech therapists, orthotists, nutritionists, respiratory therapists, psychologists and psychiatrists, home care and hospice staff. Our collective goal is to keep you and your family informed and to assist you in maintaining the highest possible level of activity and comfort and to support your informed decisions.