The intimate dovetailing of parenchymatous and connective substance in the spinal cord renders the determination of the precise origin of a morbid process often difficult if not impossible. Whatever the mode of origin, the typical termination of inflammatory and degenerative spinal disorders is sclerosis—a condition in which the essential nervous elements suffer diminution or destruction, while the connective substance is either absolutely or relatively in preponderance. The clinical result is nearly the same in all cases, and with few exceptions depends less upon the histological character than on the topographical distribution of the lesion. It is for this reason that we shall follow rather the topographical than the morbid histological principle in classification.
The chronic disorders of the spinal cord here considered have as a common character the slow and progressive displacement of the normal conducting nerve-tubes by a grayish, reddish, or otherwise discolored tissue, which is firmer in texture than normal nerve-substance. Minute examination shows that it is above all the myelin of the nerve-tubes that is wasted or destroyed, while the axis-cylinders may share in this dissolution, or, as in one form of sclerosis, they may persist and even continue in their conducting function. This increased consistency is found to be due to the increase of connective-tissue trabeculæ and of the neuroglia. In some cases this increase is active and absolute, like the increase in certain phases of hepatic cirrhosis; in others it is rather relative and passive, being merely a condensation of the connective framework after the intervening elements have wasted away, just as the texture of a compressed sponge is more compact than that of an expanded one.
Crudely, the affections of the cord characterized by this change may be divided into two great groups—the regular and the irregular. The former are characterized by their limitation to special nerve-tracts. Thus, in primary lateral sclerosis we find a special tract in the posterior part of the lateral columns occupied by the lesion. A number of spinal diseases with well-defined symptoms are due to active morbid processes which similarly follow the normal distribution of the great nerve-tracts of the cord, with the same, almost mathematical, regularity with which the medullary white develops in the fœtal and infantile cord. In another class of cases we find that the same tracts are involved in like manner—not in the way of primary disease, but through the interruption of the physiological continuity of the nerve-tract by some other disease, to which the sclerosis is therefore secondary. These are the so-called secondary degenerations.
The irregular affections of the cord comprise cases in which the sclerotic foci are either disseminated through the cerebro-spinal axis in numerous foci, or diffusely involve a greater or lesser length and thickness of the medullary cylinder, or, finally, extend in the transverse plane completely or nearly so across the section area of the cord at a definite level.
As the symptoms of the regular affections of the cord are by far the most readily recognizable, and a preliminary knowledge of them will facilitate the better understanding of the irregular forms, we shall consider the former first. They may be subdivided into two groups. The largest, longest known, and best studied consists of acquired, the other, containing less numerous cases and varieties, and rendered familiar to the profession only within the last decade, comprises the spinal disorders due to defective development of the cerebro-spinal and spinal-fibro systems.
Tabes Dorsalis.
SYNONYMS.—Locomotor ataxia and ataxy, Posterior spinal sclerosis; Graue degeneration der Hinterstränge (Leyden), Rückenmarksdarre (popular), Rückenmarksschwindsucht; Tabes dorsualis (Romberg); Ataxie locomotrice progressive (Duchenne).
HISTORY.—Undoubtedly, this disease must have been observed by the ancient masters of medicine, but their descriptions group together so many symptoms of other organic as well as functional diseases of the cord that it is impossible to obtain a clear idea as to what special form they had in view when they spoke of tabes dorsualis. This term was adopted by the German writers of the last and the earlier part of this century as designating all wasting affections of the cord; and it was not till Romberg in 1853 and Duchenne in 1858 differentiated the characteristic clinical signs, and Cruveilhier and Todd (1847) determined the distribution of the lesion in the posterior columns, that the medical profession began to recognize the distinctness of this the most common form of organic spinal ailment.
At this time, when tabes dorsalis became recognized as a clinical entity depending on sclerotic degeneration of the posterior segment of the cord, the inco-ordination or ataxia manifested in the peculiar gait of the patient was regarded as the most characteristic, essential, and constant symptom of the disease. It was regarded as an axiom in physiology that the posterior segment of the cord was subservient to centripetal and sensory conduction, and nothing appeared to follow more naturally than the conclusion that the patient exhibited inco-ordination because, his sensory conduction being interrupted or destroyed, he had lost the necessary gauge for judging of the required extent and force of a given movement. Since then both spinal physiology and pathology have undergone a profound revolution. So far are we to-day from regarding anterior and motor or posterior and sensory as convertible terms that we locate the most important centrifugal tract of the cord behind the plane which divides it into anterior and posterior halves, while the most recently differentiated centripetal tract is represented by Gowers as lying in front of it. It has been determined, through Türck, Bouchard, and Flechsig and his pupils, that the posterior white columns of the cord contain several systems of fibres, whose functions—where determinable—are of an exceedingly complex nature. The elaborate investigations of Charcot, Schultze, and Strümpell, made during the past decade, have shown that the distribution of the diseased field in the posterior segment is not uniform, but is most intense in special areas. These were found to be affected with a remarkable constancy and regularity. Almost coeval with this discovery came the recognition of symptoms found in the earliest phases of the disorder by Westphal, which, attributable as they were found to be to the involvement of the special reflex mechanisms of the cord, enable us to demonstrate the existence and extent of the disease at periods which previously were not within the ken of the clinician. The reproach which Leyden was justified in making, that most tabic patients pass through the pre-ataxic phase of their disorder under the diagnosis of rheumatism or some similar affection, can now no longer be made. Our ability to recognize the advent of this disease has reached such a degree of refinement that the question arises whether we are always justified in alarming a patient who has a prospect of remaining free from invalidating complications for many years with the announcement of a disease which, above all other spinal affections, is looked upon with dread as equally hopeless, insidious, and distressing.