else are these than persistent contractions or tonic tics, alternating or co-existing with jerking movements or clonic tics?
We have no desire, of course, to over-estimate the argumentative value of this passage, the interest of which is mainly historical; but we find ourselves wholly in accord with Cruchet when he remarks of the scientific distinction formulated by Willis, and again by Michael Etmüller, between continuous, permanent tonic convulsions, and intermittent, momentary clonic convulsions, that it is uninvolved, practical, and of universal applicability.
In 1768 certain tics were classified among the tonic convulsions by Boissier de Sauvages. Marshal Hall7 gave an account of various tonic facial convulsions to which Valleix refers as non-dolorous tics or idiopathic convulsions of the face. Coming nearer to our own times, we find the distinction of which we have been speaking again elaborated by Jaccoud,8 in 1870, and accepted also by Rosenthal.
Doubtless physiologists and pathologists are not invariably at one as regards the proper characters of the two, and subdivisions into continuous tonic contractions as opposed to intermittent tonic contractions have been deemed necessary; but without burdening the subject with a plethora of detail, we think it simple, suggestive, and clinically satisfactory to uphold Willis's generalisations and to enlist their help in the exposition of the tics. Hence, unless under special circumstances, we consider recourse to the epithet "convulsive" superfluous, and we shall employ the word tic by itself, except when there may be occasion to indicate the form of muscular contraction. The gain in conciseness is not likely to be neutralised by any loss of precision.
From our rapid survey of the vicissitudes through which the tic has passed, we may profitably gather one or two lessons.
In so far as is compatible with its nature, the schematisation of tic is indispensable. The inevitable variability of the personal factor and the absence of a real breach of continuity between any two essentially differing morbid affections ought not to deter us from the attempt to project a line of demarcation between them. Natural science is pledged to the labour of differentiation. It is the glory of Charcot's alternately synthetic and analytic work to have demonstrated the value of this method in the sphere of neuropathology. At the same time, the wisdom of attaching only a provisional importance to any scheme and of welcoming possible modification is of course self-evident. Inexact and undiscriminating inference may be a stumbling-block in the path of progress and inimical to the cultivation of the faculty of observation. Further, inaccuracy of definition not only exaggerates the liability to misunderstanding, but has sometimes also the disadvantage of promoting an illusory belief in the possession of the truth.
CHAPTER III
THE PATHOGENY OF TIC
TIC AND SPASM
Our study of tic can be approached only after a preliminary understanding as to the meaning of two words too frequently confounded even in scientific literature —tic and spasm. Let us explain, then, once for all, exactly what we intend by the latter.
Etymologically (σπασμὁς, σπἁω, I draw) the word signifies a twitch, but as it is unfortunately considered a synonym for convulsion, the two expressions are used indifferently in medical parlance, though the desirability of restricting the application of the former has more than once been indicated. Littré's definition – "an involuntary contraction of muscles, more particularly of those not under voluntary control" – may appear somewhat idle, as the contraction of muscles not under the influence of the will can scarcely be other than involuntary. His intention was, no doubt, to reserve spasm for convulsive phenomena in non-striped muscle fibres; but in this limited sense the term has not met with acceptance, and it remains equivalent to "involuntary muscular contraction," whatever that may mean. Thus interpreted, it is applicable to any and every involuntary muscular movement, physiological and pathological, to the inco-ordination of tabes, to chorea, athetosis, tremor, etc.
Rather than imagine a new substantive to characterise certain of these muscle contractions, we may retain the word in a somewhat wider though equally precise sense, and follow the distinction drawn by Brissaud9 in 1893: "a spasm is the result of sudden transitory irritation of any point in a reflex arc; … it is a reflex act of purely spinal or bulbo-spinal origin."
By definition, then, a spasm is the motor reaction consequent on stimulation of some point in a reflex spinal or bulbo-spinal arc. To differentiate between the reflex, which is physiological, and the spasm, which is pathological, we may add as a corollary: the irritation provocative of the spasm is itself of pathological origin, and no spasm can occur without it. The anatomo-pathological substratum of a spasm is, then, some focus of irritation on a spinal or bulbo-spinal reflex arc, which may be situated in peripheral end organ, in centripetal path, in medullary centre, or in centrifugal fibre. Whatever be its localisation, it will determine a spasm in our sense of the word.
Cortical or subcortical excitation, however, as well as peripheral stimuli, may provoke these bulbar and spinal centres to activity. Irritation of a point on the rolandic cortex, or on the cortico-spinal centripetal paths, is followed by a motor reaction exactly as with afferent impulses; the sole change is in the route taken by the centripetal stimulus; the reflex centre remains bulbo-spinal, and the efferent limb of the arc is as before.
The application of the word spasm to these motor responses to cortical or subcortical stimulation is quite justifiable. Developmentally the grey matter of the cerebral convolutions is ectodermic, as is the skin, and capable of functioning as a sensory surface; it may be considered the end organ of an afferent path that conducts to medullary reflex centres. According to our definition, then, provided the centre of the reflex arc be bulbo-spinal and the irritation pathological, the consequent motor phenomenon is a spasm.
A distinction most nevertheless be drawn between the two cases, inasmuch as in the one the afferent path is peripheral, in the other it is cortico-spinal, and there is a corresponding difference in the clinical picture. Jacksonian convulsions, consecutive to cortical stimulation, do not seem to bear much resemblance to spasmodic movements indicative of peripheral —i. e. sensory nerve – irritation. As a matter of fact, it is not always easy to differentiate the two, except by the aid of concomitant phenomena. The characteristic evolution of the Jacksonian convulsion is of course readily recognisable. We can similarly diagnose an irritative lesion of the internal capsule not so much from the objective features of the convulsive movements as from accompanying indications. In short, there need never be any occasion for confusion. Convulsive conditions attributable to irritation of cortico-spinal centripetal paths have long been described and analysed: they constitute well-recognised morbid entities, among which may be enumerated Jacksonian epilepsy, hemichorea, hemiathetosis, pre-and post-hemiplegic hemitremor, etc.
These clinical denominations for the affections under consideration it is at present desirable to retain. We shall not call them spasms; above all, we must not call them tics, else we shall end by confounding conditions absolutely distinct. The case recorded by Lewin,10 under the title of "convulsive tic," of a three-year-old infant still unable to walk, who has daily attacks in which "all the muscles" twitch for about a minute at a time, is indeed a most singular tic. We were under the impression that such an attack is usually known as an epileptiform convulsion. Is the term "convulsive tic" quite a happy synonym?
Again, in the recent thesis of Cruchet the attempt has been made to base the pathological physiology of tic on researches of von Monakow and Muratow apropos of the occurrence of choreic, epileptoid, or athetotic movements after certain lesions of the cerebro-spinal axis, and to find an analogy in the action of various convulsion-producing substances (Richet and Langlois). Cruchet's conclusion is that convulsive tic is as often cortical or subcortical as spinal in origin; that it is, in short, a mere symptom, common to many cerebro-spinal conditions.
The same regrettable confusion is discernible in various treatises on neuropathology the work of German and other foreign authors.
As far as we are concerned, the outcome of the whole matter is simply this: if tic is doomed to be used indifferently for convulsion, its retention in scientific terminology