There cannot possibly be any hesitation in arriving at a diagnosis between tonic tic and Thomsen's disease, a condition consisting in slowness of relaxation of a strongly contracted muscle, and conceivably due to defective metabolism or organic change in muscular tissue.[187]
Examples such as the above, culled at random from an abundant medical literature, and variously entitled, will serve to demonstrate the protean nature of what the medical world is content to call myoclonus, and if from this collection of motor disorders we may hope to extricate the tics, there will remain still no inconsiderable labour of differentiation for the student.
TIC AND ATHETOSIS
The athetotic movements that may accompany hemiplegia are scarcely likely to be confused with those of tic, but difficulties may arise where the athetosis is double.
It has been universally remarked that athetotic movements of the face reproduce the expression of emotions, such as admiration, astonishment, sorrow, gaiety, etc. Of course the same may be said of the grimaces of chorea; the latter, however, are usually more abrupt and pass less readily one into the other. The gesticulations of athetosis are undulatory, so to speak, and their excess leads to deformities principally in the direction of forced extension. The musculature is often rigid, and the reflexes are increased in activity. Sometimes there is a considerable degree of mental disturbance.
Now, it is precisely in cases where mental deterioration is a prominent feature that "nervous movements" have been described resembling those of athetosis, for which the term pseudo-athetosis has been coined. Two examples may be quoted from Noir.
E. is a girl of eleven years. Her expression is grimacing; her tongue is often protruded, but never bitten; her head is regularly flexed or extended, or rotated rhythmically to left or right. The arms are moved spasmodically at shoulder and elbow, while the hands are the seat of athetotic movements. She walks curiously, throwing her feet out in advance without bending her knees. She has a silly smile, and her mouth almost invariably hangs open. On request she can keep her hands quite steady, but one observes at once the effort this entails in the sudden seriousness of her expression. The ordinary acts of every-day life are performed satisfactorily enough: she can dress and undress, use a knife and fork, thread a needle, sew, etc.
J. is eleven years old also. She puckers her lips, contracts her eyebrows, elevates her alæ nasi; at the same time she exhibits pseudo-athetotic movements of her fingers which are entirely under voluntary control.
The question may indeed be asked whether pseudo-athetosis and variable chorea are not really identical. Further, all sorts of combinations of athetosis and myotonia have been noted,[188] but more light must be shed on the subject before any further classification can be attempted.
The following case has recently been published by Marina[189]: