Yet here, again, peril lurks in too hasty a generalisation. To give the disease a name is not equivalent to pronouncing a diagnosis. The denominations "myoclonus," "muscular dystrophy," "degenerate," are alike inconvenient. Their scope is at once too inclusive and too exclusive. They may be indispensable; they are assuredly not sufficient.
The possibilities of misapprehension do not end here.
The manifestation of each and every tic—be it a flicker of the eyelid, a turn of the head, a cry, a cough—is through the medium of a muscular contraction. On the very nature of this contraction opinion is divided.
To its distinctive features of abruptness and momentariness is due the epithet "convulsive" habitually assigned it, but the qualification is not secure. Since the time of Willis the word convulsion has been employed in a double sense, to signify clonic muscular contractions (the "convulsion" of popular parlance) and tonic muscular contractions (a meaning attached to the term only by the scientist).
For our part, we can raise no valid objection to the specification of tics as convulsive, provided always that the existence of clonic convulsive tics and of tonic convulsive tics be recognised. As a matter of fact, clinical observation supplies instances of both sorts.
Nevertheless, attention has been confined by a majority of authors to the consideration of the former variety only, so much so that a whole order of facts which in derivation, essence, and external characteristics ought to be identified with the tics has been passed over in silence. Even on the assumption that the proposal to recognise the two classes cannot be entertained, at the least it is advisable to predetermine the import of the word convulsion, and to speak of clonic convulsive tics. This is the formula of Ferrand and Widal in their article "Convulsion" in the Encyclopædic Dictionary of the Medical Sciences. Similarly, Troisier[6] says that the convulsive tic properly so called is characterised by clonic movements, in which opinion Erb and most German observers concur. Tonic tic appears to have been forgotten, and we have thought it our duty to resuscitate it.
Cruchet has quite recently approached the subject in a critical fashion:
To extend the term tic to tonic spasms such as mental torticollis, mental trismus, or permanent blepharospasm, is singularly to outstep the limits of its significance. We believe Erb, Troisier, and Oppenheim are warranted in restricting convulsive tic to clonic convulsions, and the consequent simplification and elucidation of the question lead us to adopt the same view.
If it be solely a matter of terminology, and if universal consent reserve tic for convulsions whose expression is clonic, we shall be the first to withdraw the phrase "tonic tic," making the single proviso that some other designation be found for a condition which differs from the clonic tic only in its external features, and not in origin, pathogeny, or treatment.
What is this other name to be? Are these tonic muscular contractions to be regarded as synonymous with contractures? If so, do we mean myotetanic contracture—to utilise the excellent division imagined by Pitres—as in hysteria, or myotonic contracture, as in Parkinson's disease? The state of muscular contraction in tonic tic does not correspond accurately to either, though it is certainly more akin to the myotonic form; but myotonia is a sort of caput mortuum for the too facile classification of cases in reality difficult to place, and we are afraid the term is not calculated to ensure precision of ideas.