The morbid process of disseminated sclerosis consists in the development of patches of sclerosed tissue, scattered apparently without any regularity or rule through the brain and spinal cord. They are the results of insidious inflammatory changes. The symptoms marking their presence may include nearly every known focal and general symptom studied by neurologists, varying with the number, size, and distribution of the foci. Usually there is some disturbance of motility, both ataxic and paretic; in the majority there is tremor, which in a large proportion of cases is of a distinctive character, and disturbance of the functions of the cranial nerves, amblyopia, color-blindness, mental enfeeblement; and, above all, apoplectiform seizures are frequent.
Some writers discriminate between cases in which the lesions are limited to, or most intense in, the spinal cord, and those in which the brain is chiefly or exclusively involved, and hence they speak of a spinal, a cerebral, and a cerebro-spinal form. This discrimination is not sufficiently supported by clinical evidence to be of any practical value. Each case is to be studied by itself during life and after death, and to be regarded as one of a series in which the lesion may be concentrated in any one segment of the cerebro-spinal axis. It seems that when the sclerotic foci are limited to or chiefly located in the spinal cord, the clinical signs are less pronounced than where the brain is seriously involved; those cases in which the symptoms are latent, or so vague that they cannot be distinguished from spinal irritation or spinal exhaustion, have been found to be of the spinal type. The cases of this character thus far observed are not sufficiently numerous to justify the creation of special subdivisions.115
115 According as the formation of the sclerotic foci preponderates in a given segment of the nervous axis, the early signs of the disease may consist in disturbances of the cerebral or the spinal functions, and we may speak accordingly of a cerebral or spinal invasion type. But the principle of classification adopted by several recent writers, which would rank the spinal type among the spinal diseases, the cerebral type among the cerebral diseases, and which is compelled to erect a third category for the reception of the cerebro-spinal type under the name of cerebro-spinal diseases, is a bad one. Modern pathology recognizes the existence of affections which involve whole fibre-systems, which are intracerebral in one and intraspinal in other parts of their course, such as tabes and amyotrophic sclerosis, which would therefore have to rank among the cerebro-spinal, and not among the spinal affections, with which the authors referred to classify them.
CLINICAL HISTORY.—Prodromal.—Disseminated sclerosis is usually inaugurated by a long initial period in which the symptoms are not characteristic, and in which, unless there be decisive pupillary or optic-nerve symptoms present, the nature of the disease is not recognized. The patients feel weak and tired; walking is difficult, and an element of unsteadiness suggests the development of a tabic disorder. In other cases ankle-clonus is found and tremor of the foot on extension (dorsiflexion); it is discovered that the unsteadiness is due to weakness or to rigidity of the muscles, and thus the impression of a developing spastic paralysis may be created. But symptoms on the part of the cranial nerves soon show that the case is one of disseminated sclerosis. Sometimes a marked belt sensation is developed, and other forms of paræsthesia are not uncommon; nay, the symptoms of spastic paralysis and tabes dorsalis may be mingled. Diplopia of the same transitory character as in tabes usually accompanies the gradually-developing speech trouble. The reflex and mechanical excitability of the muscles is increased in all cases where the lateral column is extensively involved and the gray substance of the cord is—as it usually is in the main—intact. In some cases a slight tap on the knee when held in the position required to demonstrate the knee-jerk produces oscillatory movements of the limb; as the patient endeavors to suppress these they become more violent, extend to the trunk and head, and may eventually involve the opposite side. In those cases which show the cerebral-invasion type headache, vertigo, and speech disturbance, temporary darkening of the visual field, and loss of memory are the earliest symptoms directing attention to the existence of serious disease.
Whether the spinal or the cerebral symptoms preponderate, they continue increasing slowly and with temporary variations, which are particularly marked in the cerebral-invasion type. As a rule, the sensory disturbances are not pronounced at this time, but later, after the initial symptoms have existed for a few years, they become intense, and often extremely distressing. Those most complained of by the patient are neuralgic, lancinating, and other pains. The lancinating pains are, as a rule, not as severe as those of tabes dorsalis, but they are apt to be associated with a dull heavy pain which is located in a whole extremity, referred to the deep structures, and very persistent. This diffuse pain sometimes occupies all of the lower half of the body. As in tabes, the pain may be regarded the forerunner of anæsthesia, which rarely, however, reaches a high degree or an extensive distribution. Its distribution, like that of the other peripheral symptoms of disseminated sclerosis, is commonly irregular. Like the motor disturbance, which at this period consists in a combination of paretic and spastic—occasionally of ataxic—symptoms, it is most marked in the lower extremities.
In the majority of cases there is a peculiar tremor, which usually presents the character to which Charcot directed attention—namely, that it increases when the patient attempts to carry out a voluntary movement, and disappears, or at least diminishes, when the muscles of the part in question are at rest. This is the important symptom known as the tremor on intended movement or intention tremor. One of the time-honored means of testing it is to order the patient to take a glass of water and pass it to his mouth. While he reaches out for it some oscillatory unsteadiness is observed, but on grasping, this is increased, and on raising the glass the oscillations increase till he spills the water; if he succeeds in carrying it to his mouth, there is a clattering against the teeth, and but for the steadying aid of his mouth he would throw it aside by the violence of the disturbing movements. In incipient cases this intention tremor is best shown with delicate movements, and the more distinctly the more slowly they are performed. It has been suggested that the peculiar character of the lesion of disseminated sclerosis has some relation to the intention tremor. It is a remarkable feature of the morbid process that it leaves the axis-cylinder comparatively intact, beyond any other form of myelitis or encephalitis. The myelin, however, is destroyed, and the consequence is that the naked axis-cylinders lie in a newly-formed connective tissue, which has not the same faculty the myelin has of isolating the nervous impulses conducted through the axis-cylinders. The result is, that when a nervous impulse, such as a voluntary movement, travels through a sclerotic focus, it may become deflected to neighboring fibres going to another muscle or muscular bundle than the one intended to be innervated. An unintended motion results; the patient makes a stronger effort, intended for the right channel, but again it slips off, to use a coarse simile, and thus a number of erroneous messages are transmitted, and an equal number of disturbing motions respond to these messages.
Whether this histological explanation be correct or not, the tremor is probably due to the lesion of the peduncular tracts of the brain. At least, this is rendered plausible for the tremor on intended movement, which indicates an interference with the transmission of voluntary impulses. Whether, as Pasternatzky116 claims, the extreme muscular oscillation seen in advanced cases is due to irritation of the cortical motor fields, it is impossible to decide. No strong evidence can be adduced in favor of his view. A few cases have been described (Schüle, Jolly, and Greiff); and, in my opinion, such are far more numerous than is usually supposed, where the tremor did not have the so-called characteristic feature of ceasing in conditions of rest, claimed by Charcot, but continued as in paralysis agitans.117 A collection of cases by Erb, Ordenstein, and Greiff shows clearly that with a typical dissemination of sclerotic foci in the cord the tremor on intended movement may be entirely absent, while no case is known where the crus and pons were involved to a similar extent in which it was absent. So it seems that a cerebral lesion is necessary to produce this symptom in its characteristic form.
116 Jahrbücher für Psychiatrie, iii. 3, 1882.
117 For several years I had been puzzled by the fact that Charcot's formula failed to correspond to the clinical picture in the majority of cases, and I registered such cases as incipient multiple sclerosis or as a connecting group between paralysis agitans and that disease.
In advanced cases of disseminated sclerosis the intention tremor becomes generalized; previously noticed, perhaps, only in one arm, it now affects all the limbs and the muscles which maintain the trunk and head in static equilibrium. The result is, that even when the patient is at rest sitting in a chair, his body, and particularly his head, are agitated by a violent and coarse tremor, which is increased on rising and walking, as well as on attempting to use the hands. Delicate mechanical occupations become impossible, and the handwriting shows a characteristic change, the forward strokes of the letters and the curvilinear back strokes, as well as the dots and crosses, registering the tremor of the hand in their peculiar irregularity.