Amyotrophic Lateral Sclerosis.
Amyotrophic lateral sclerosis, so named by Charcot104 and Joffroy, who first described it, consists in a disease affecting both the conducting tracts and nuclear centres of the motor system of the spinal cord and medulla oblongata, manifesting itself in a combination of atrophic and irritative phenomena on the part of the muscles. The relations between the symptoms and lesions of this disease rival in constancy and preciseness those noted in typical tabes dorsalis. As the variations in the mode of invasion and distribution of the lesion account for the widely-differing clinical types of the disease, and the advanced state of our anatomical and physiological knowledge of the cord enables us to interpret the reason of this difference, we shall invert the usual order and discuss the morbid anatomy first.
104 In 1869 and 1874 (Leçons sur les Maladies de la Système nerveux) Charcot termed this, and one other form of disease associated with muscular atrophy, amyotrophic, to distinguish them from the myopathic forms. He considers amyotrophic lateral sclerosis as deuteropathic, the nuclear atrophy being secondary to the lesion of the white substance, and the progressive muscular atrophy of the type described by Duchenne and Aran as a protopathic form of the amyotrophies. Among the true myopathies he enumerates pseudo-hypertrophic paralysis, Erb's juvenile form, Duchenne's infantile form, certain mixed forms, and, without justification, Leyden's hereditary forms (report by Marie et Guivron, Progrès médicale, 1885, No. 10).
MORBID ANATOMY.—In advanced cases of amyotrophic lateral sclerosis there is found marked sclerotic degeneration of both the crossed and the uncrossed pyramid tracts; atrophy of the cells of the anterior horns; atrophy of some of the nuclei of the motor and mixed cranial nerve, particularly the hypoglossal and spinal accessory; atrophy of the anterior roots of the spinal and the roots of certain motor cranial nerves; and, finally, atrophy of the voluntary muscles. The greater part of the tract through which the voluntary impulse travels after leaving the voluntary motor-fields of the cortex is therefore continuously involved; and it would seem that there are cases (Kahler-Pick's) where the entire motor system is affected, the morbid process demarcating the course taken by the motor impulse through the cerebro-spinal fibre-labyrinth from the cortical motor-field down to the muscles.
The morbid process in the muscles consists of a narrowing of the fibres, which subsequently lose their transverse striation and undergo a granular disintegration. Sometimes a muscle disappears entirely; usually the connective-tissue elements, including the interstitial cellular and adipose tissue, undergo proliferation, so as to mask the wasting of the muscles to some extent.
The morbid process in the nervous system is also a simple degenerative process. The nerve-fibres and cells atrophy first, and the connective-tissue proliferation which marks the sclerotic change of the diseased area is a secondary process. There is still considerable dispute among authorities as to which segment of the motor-conduits the degeneration begins in. But from the great difference found in the individual cases which have become the subject of patho-anatomical studies there can be little doubt that there is no uniformity in this respect. In some cases the lesion is far advanced in the lateral columns, while the anterior horn is but slightly involved; in others the reverse is found. Sometimes the nuclei of the motor cranial nerves are the chief foci of disease; at others they are the least affected parts of the motor apparatus. As we shall see, there are differences in the clinical picture corresponding to the variations of the anatomical findings.
CLINICAL HISTORY.—In typical cases the first symptom is a tired feeling in one arm or leg, usually the former; in dextral persons the right arm, the one which is subject to the severest strain, is most frequently the first to be affected. With the increase in this tired feeling there develops actual loss of power; the muscles become wasted, and the other arm becomes involved. Often it is observed that the right leg suffers with the corresponding arm, but as a rule the lower extremities do not become involved to any marked degree within the first six months of the illness. It is then noted that a gait not unlike that of spastic paralysis is noted, but with more loss of motor power and less stiffness. There is, however, this noteworthy difference between the affection of the lower and that of the upper extremities: that atrophy and loss of power are more marked in the latter, and spastic phenomena in the former. The knee-jerk and other deep reflexes are greatly increased, and ankle-clonus is usually very well marked. As with spastic paralysis, there are no visceral or sensory disturbances. Unlike that affection, there are qualitative changes in the electrical reaction of the muscles105 in amyotrophic lateral sclerosis. The degeneration reaction is found in the atrophied divisions, and particularly in such groups as those of the thenar and hypothenar eminence, which undergo complete atrophy at a comparatively early period of the disease.
105 Moeli, Strümpell, Pick, and Mierzejewski describe cases in which only quantitative changes were found. They were such in which spastic phenomena preponderated at the time of the examination.
Soon after the spastic and atrophic involvements of the lower extremities, symptoms indicating the involvement of the cranial nerve-nuclei are developed, usually after the disease has lasted a year or so. Deglutition becomes difficult and speech indistinct, the general picture of a glosso-labio-laryngeal paralysis being imitated. The patient cannot pucker his lips, his lingual muscles undergo atrophy, and fibrillary and fascicular twitches are noted in the tongue and lips. But just as the atrophic affection of the muscles of the arms and legs differs from that of progressive muscular atrophy in the fact that the deep reflexes are exaggerated with amyotrophic sclerosis, so in the bulbar symptoms of the latter it is found, unlike the typical form of bulbar paralysis, that the jaw reflex is increased.
The duration of the disease may be stated at about three years, death usually occurring in consequence of the involvement of the cranial nerves. There are cases recorded where the disease was almost simultaneously developed in all four extremities and the tongue, reaching a high degree within a year (Mierzejewski). It is generally agreed that the reason contractures do not develop in typical cases of this kind, although the lateral column is sclerosed and spastic phenomena occur early in the disease, is the destruction of the cell-groups in the anterior horn. The reflex arch through which a reflex contracture would be mediated is broken, or rather weakened, in that part of its course which passes through these cells, and therefore a contracture is as efficiently antagonized as it would be if the posterior roots were divided. Still, in some cases a frozen attitude of the lower extremities is very well marked (Vierordt, Zacher). To reconcile these conflicting observations it has been suggested that it may be regarded as a question of speed between the progress of the pyramid-tract and the anterior-horn lesions. If the former be much in advance of the latter, spastic phenomena will preponderate and contractures be possible, to disappear with the subsequent anterior-horn lesion. But if the latter precede and preponderate, the spastic phenomena will be in the background and contractures impossible. Indeed, Zacher106 suggests that there may be an ascending form in which the lesion of the pyramid tract is secondary to the nuclear atrophy, corresponding to the typical class of cases on which Charcot based his first description of the disease, and a descending form in which the pyramid tract is first affected and the nuclear cell-groups follow. Vierordt107 and Kahler108 express similar opinions. The latter goes so far as to suggest that progressive muscular atrophy, progressive glosso-labio-laryngeal paralysis, and amyotrophic lateral sclerosis are really due to one and the same kind of degenerative process, merely differing in location. There is certainly, as he claims, a remarkably complete chain of cases, beginning with such (1) in which spastic paralysis preponderates, passing thence to (2) those in which some muscular atrophy preponderates, then (3) those in which muscular atrophy is in the foreground and the spastic phenomena are slight, and ending with (4) the pure atrophies. A similar transition may be established on the regional principle between pure glosso-labio-laryngeal paralysis and amyotrophic lateral sclerosis, for there are cases of this affection in which the oblongata symptoms preponderate throughout, and the focus of the disease is formed there, just enough lesion being demonstrable in the pyramid tract and the spinal gray matter to prove the family relationship of what clinically appears as a spastic bulbar paralysis.109