It has been proposed that all degenerative diseases be classified according to their genetic and molecular abnormalities. However, when one notes the diversity of pathologic change that may accompany a single, seemingly unitary gene abnormality or, reciprocally, the diversity of genetic defects that may underlie a single phenotype, this type of classification does not prove immediately helpful to the clinician. In other words, the practice of creating new disease categories to encompass all the molecular and pathologic changes associated with a particular type of neuronal degeneration offers no great advantage in practice. For example, certain diseases are unified by the deposition of proteins and have been termed “tauopathies,” “synucleinopathies,” “amyloidopathies,” and so forth. We endorse a more useful clinical approach that is based on an awareness of constellations of clinical features that relate to degeneration of specific neural systems. Until such time as the causation of the degenerative neurologic diseases is known, there must be a name and a place for a group of diseases that are united only by the common attribute of gradually progressive disintegration of a part or parts of the nervous system.
General Clinical Characteristics of Degenerative Diseases
As mentioned, the diseases included in the degenerative category have 2 outstanding characteristics: (1) They affect specific parts or functional systems of the nervous system, and (2) They begin insidiously, after a long period of normal nervous system function, and pursue a gradually progressive course. Frequently, it is impossible to assign a date of onset. The patient or the patient’s family may give a history of the abrupt appearance of disability, particularly if some injury, infection, surgical procedure, stroke, or other memorable event coincided with the initial symptoms. A skillfully taken history will reveal that there had been subtle symptoms for some time but had attracted little attention. Whether a dramatic life event can actually evoke or aggravate a degenerative disease is a question that cannot be answered with certainty; evidence to this effect is largely anecdotal. Instead, these degenerative disease processes, by their very nature, appear to develop de novo, without relation to known antecedent events, and their symptomatic expressions are late events in the pathologic process, occurring only when the degree of neuronal loss exceeds the ability of a system to function at a clinically acceptable level. Irreversibility and steady progression of clinical manifestations when measured over periods of months or years is another feature common to the neurodegenerative conditions. However, several of these diseases sometimes display periods of relative stability.
Although most degenerative disease do not manifest expression in other members of the family, the familial occurrence of degenerative disease is of great importance both clinically and for scientific reasons as mentioned earlier, but such information is often difficult to obtain. The family may be small or widely scattered, so that the patient is unaware of the health of other members. The patient or the patient’s relatives may be reluctant to acknowledge that a neurologic disease has affected another family member. Furthermore, it may not be realized that an illness is hereditary if other members of the family have a much more or much less severe, or a different form of the disorder than the patient. Or paternity may be in question. Sometimes, only the careful examination of other family members will disclose the presence of a hereditary disease. Also, it should be remembered that familial occurrence of a disease does not necessarily mean that it is inherited, but may indicate instead that more than 1 member of a family had been exposed to the same infectious or toxic agent.
Many symptoms of degenerative disease, while not currently curable, can be alleviated by skillful management. The physician’s interest and advice are invaluable to the patient and his family by way of providing support, perspective, and information. This accords with the highest calling of the physician’s abilities to relieve suffering.