ALS, MS, MD- WHATS THE DIFFERENCE? By Charles Plank A major reason for confusion about two very distinct neurological dis- eases amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) is the word, "sclerosis," which literal- ly means hardening (as a result of increased connective tissiie or glia). Other reasons for the confu- sion are that both diseases are pri- mary neurological diseases, often or usually affecting the spinal cord, and that they typically result in dif- fictilties with gait an 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, le- sions can be and typically are at multiple sites. The disease, howev- er, affects only central myelin, not the myelin of peripheral nerves. Therefore, the symptoms are spe- cifically of a central nervous system disorder. Other elements of central ner- vous tissue (the actual nerve cells, their processes and axis cylinders, and the supporting tissue) are rela- tively 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 ax- --------------------------------------------- CHARLES PLANK. M.D., is an associate in clini- cal neurology at the Neurological Institute, Columbia University, and neuropathology at Harlem Hospital Center, N.Y. He is also in private practice of general neurology with a special interest in multiple sclerosis and is a guest investigator at Rockefeller University Hospital, N.Y., for evaluation of MS patients. --------------------------------------------- ons themselves. That is, nerve cells, surprisingly, do not show sigiiifi- cant evidence of destruction. Another striking feature of the pathology of multiple sclerosis is inflammation. The collections of in- flammatory cells are perivascitlar in location and seem related to the lesions themselves. Their exact role is, however, not completely under- stood. The principle characteristic in the pathology of amvotropliic lat- eral sclerosis(ALS) is loss of motor nerve cells in the anterior honis of the spinal cord and in the motor nticlei of the brain stem. This re- sults in secondary atrophy of the corresponding muscles (amyotro- phy). There is no evidence of in- flammation, either as a primary or a secondary phenomenon. "Lateral sclerosis" refers to corticospinal tract degeneration (lateral in loca- tion in the spinal cord). In fact, myelin loss occurs in the corticospi- nal tract, but this is thought to be secondary to the neuronal and ax- onal loss. Thus, it is not primary demyelination, as it is in miiltiple sclerosis, that is the primary de- structive effect in ALS. The sclero- sis of ALS, the hardening, involves oniv the lateral columns, or corti- cospinal tracts and is a secondary phenomenon. The cells of the anterior horns involved in ALS are the cells re- sponsible 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 dis- ease the characteristic, or appear- ance, of being peripheral, although it is very clearly not. Amyotrophic lateral sclerosis is sometimes referred to as muscu- lar atrophy. This muscular atrophy is a phenomenon secondary to the disorder of innervation. Perhaps this descriptive term has contrib- uted somewhat to the confusion with muscular dystrophy. Confu- sion with multiple sclerosis, al- though more frequent, is more diffi- cult to explain. Amyotrophic lateral sclerosis may not be symmetrical at the time of onset, but it becomes more sym- metrical as the disease progresses. That is, patients often present to neurologists with complaints refer- able to one side of the body. Exam- ination confirms that both sides are involved, but it iiiav not be until some weeks or months later that the patient is aware of the bilateral involvement so typical of the dis- ease. ALS also does not affect sen- sation, which is a characteristic im- portant in making the diagnosis. Multiple sclerosis, on the other hand, is usually asymmetrical in presentation and progression. Sen- sation can be and frequently is affected because of demyelination in those parts of the central nervous system where sensation is transmit- ted. Muscular dystrophies are dis- eases characterized by symmetrical distribution of muscular weakness and atrophy,. Sensation is complete- ly unaffected. Althotigh muscular dystrophy (MD) is often confused with MS and ALS, it is a verv dis- tinct disease group; the pathologi- cal differences are even greater. These are not diseases of the central or peripheral nervous svsteins, but exclusively of muscle. The most widely known of the muscular dystrophies is Du- chebbe's, which affects the child or adolescent, and the life duration is only a few years. On the other hand, myotonic muscular dystrophy af- fects the young adult and usually lasts longer than 20 vears. There are forms of muscular dystrophic that result in minimal disability and do not significantly shorten life. The muscular dystrophies are heredi- tary. Most are atitosomal dominant. Usually their inexorable proaress is slow, but characteristically steady. Multiple sclerosis rarelv 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 inci- dence 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 sib- ling 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, depend- ing on frequency, severity, and lo- cation of attacks. A small number of patients die within a few months or years of the onset, but for most patients, the overall duration ex ceeds 20 vears. In some, the afflic- tion 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 inher- ited, but there is a form (infrequent ly encountered) that is transmitted from generation to generation. No specific treatment for an of these diseases has been satisfac- tory, despite efforts of physicians, researchers, and very active organi- zations devoted to each disease. At attemps at symptom management are very important and are, unfor- tunately, all we have now.