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ALS, MS, MD-
WHAT'S THE DIFFERENCE?

By Charles Plank

A major reason for confusion about two very distinct neurological diseases amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) is the word, "sclerosis," which literally means hardening (as a result of increased connective tissue or glia).

Other reasons for the confusion are that both diseases are primary neurological diseases, often or usually affecting the spinal cord, and that they typically result in difficulties with gait and strength. An easy way to differentiate between these two is to understand the basic differences in the pathology and the progression of this pathology.

Multiple sclerosis is a disease of myelin, not primarily of nerve cells. This myelin surrounds the axons, or the long process of the nerve cell. Since myelin occurs throughout the nervous system, lesions can be and typically are at multiple sites. The disease, however, affects only central myelin, not the myelin of peripheral nerves. Therefore, the symptoms are specifically of a central nervous system disorder.

Other elements of central nervous tissue (the actual nerve cells, their processes and axis cylinders, and the supporting tissue) are relatively spared. Any neuronal damage is secondary to the destruction of the myelin covering of the axon, but does not result in significant retrograde degeneration of the axons themselves. That is, nerve cells, surprisingly, do not show significant evidence of destruction.

Another striking feature of the pathology of multiple sclerosis is inflammation. The collections of inflammatory cells are perivascular in location and seem related to the lesions themselves. Their exact role is, however, not completely understood.

The principle characteristic in the pathology of amyotrophic lateral sclerosis(ALS) is loss of motor nerve cells in the anterior horns of the spinal cord and in the motor nuclei of the brain stem. This results in secondary atrophy of the corresponding muscles (amyotrophy). There is no evidence of inflammation, either as a primary or a secondary phenomenon. "Lateral sclerosis" refers to corticospinal tract degeneration (lateral in location in the spinal cord). In fact, myelin loss occurs in the corticospinal tract, but this is thought to be secondary to the neuronal and axonal loss. Thus, it is not primary demyelination, as it is in multiple sclerosis, that is the primary destructive effect in ALS. The sclerosis of ALS, the hardening, involves only the lateral columns, or corticospinal tracts and is a secondary phenomenon.

The cells of the anterior horns involved in ALS are the cells responsible for the peripheral motor nerves. They are within the central nervous system, but this part of the disease affects the innervation of the muscles, thus lending to the disease the characteristic, or appearance, of being peripheral, although it is very clearly not.

Amyotrophic lateral sclerosis is sometimes referred to as muscular atrophy. This muscular atrophy is a phenomenon secondary to the disorder of innervation. Perhaps this descriptive term has contributed somewhat to the confusion with muscular dystrophy. Confusion with multiple sclerosis, although more frequent, is more difficult to explain.

Amyotrophic lateral sclerosis may not be symmetrical at the time of onset, but it becomes more symmetrical as the disease progresses. That is, patients often present to neurologists with complaints referable to one side of the body. Examination confirms that both sides are involved, but it may not be until some weeks or months later that the patient is aware of the bilateral involvement so typical of the disease. ALS also does not affect sensation, which is a characteristic important in making the diagnosis.

Multiple sclerosis, on the other hand, is usually asymmetrical in presentation and progression. Sensation can be and frequently is affected because of demyelination in those parts of the central nervous system where sensation is transmitted.

Muscular dystrophies are diseases characterized by symmetrical distribution of muscular weakness and atrophy. Sensation is completely unaffected. Although muscular dystrophy (MD) is often confused with MS and ALS, it is a very distinct disease group; the pathological differences are even greater. These are not diseases of the central or peripheral nervous systems, but exclusively of muscle.

The most widely known of the muscular dystrophies is Duchebbe's, which affects the child or adolescent, and the life duration is only a few years. On the other hand, myotonic muscular dystrophy affects the young adult and usually lasts longer than 20 years. There are forms of muscular dystrophic that result in minimal disability and do not significantly shorten life. The muscular dystrophies are hereditary. Most are autosomal dominant. Usually their inexorable progress is slow, but characteristically steady.

Multiple sclerosis rarely has its onset in the first decade of life. The overwhelming majority of patients realize the onset of disease between ages 20 and 40. Although the incidence is low, onset later (even into the sixth decade) can occur. The risk of developing the disease is greater in the person who has a sibling or parent with the disease, but while there seems to be a familial tendency, there is no hereditary pattern for MS. Life expectancy may be shortened in some patients with multiple sclerosis, but this shortening varies greatly, depending on frequency, severity, and location of attacks. A small number of patients die within a few months or years of the onset, but for most patients, the overall duration exceeds 20 years. In some, the affliction is so mild that they never come to the attention of a physician.

Amyotrophic lateral scierosis is a disease usually of middle life that characteristically progresses to death within two to six years. In exceptional cases, the disease has had its onset earlier or later, and the duration of the illness has been longer. It is not ordinarily inherited, but there is a form (infrequently encountered) that is transmitted from generation to generation.

No specific treatment for any of these diseases has been satisfactory, despite efforts of physicians, researchers, and very active organizations devoted to each disease. Attempts at symptom management are very important and are, unfortunately, all we have now.

ALS, MS, MD- WHAT'S THE DIFFERENCE?

By Charles Plank

ALS, MS, MD-
WHAT'S THE DIFFERENCE?