Again, if the cause of chorea in rheumatic subjects be the detach ment of particles of lymph from the surface of a roughened valve, how are we to explain its occurrence in those numerous rheumatic subjects whose valves have never been affected? To such cases this embolic theory is quite inapplicable. It cannot, therefore, be re garded as adequate. Just as Bright's theory might apply to cases of chorea occurring in connection with pericarditis, so this one might apply to cases of chorea occurring in connection with endocarditis. The fault of each is its narrowness, and the impossibility of applying it to more than a minority of the total cases of rheumatic chorea. What we want is an explanation which will apply to all cases of that disease—those occurring in connection with pericarditis—those oc curring in connection with endocarditis—those occurring in connec tion with simple rheumatism of the joints, uncomplicated by any heart affection—and those occurring in persons of rheumatic consti tution but who, at the time of the choreic attack, are not suffering from rheumatism of either the heart or joints.
The theories hitherto advanced have given prominence to two different factors—the morbid condition of the blood, and the inflamed condition of the heart. Neither has been sufficient to meet the whole of the facts. A much wider pathological view is required for that purpose.
Rheumatism is essentially a disease of the motor apparatus; chorea is essentially a disease of the motor centres. In this broad pathological statement we have the clue to the explanation of the re lation of the two diseases.
The motor centres affected in chorea, and the motor apparatus which suffers in rheumatism, have an essential physiological connec tion. The motor centres form the central portion of a system, of which the motor apparatus is the distal or peripheral. Each is essen tial to the physiological completeness of the other, and without the other neither has any physiological raison d'être. Without joints to be moved, the motor centres would be useless; without motor cen tres to initiate the necessary nervous force, the muscles would remain flaccid and the joints be of no avail.
The seat of chorea and the spat of rheumatism having so close a physiological connection, it need not surprise us to find that there is some connection between these two diseases, and that those who are subject to the latter are also liable to have the former.
The existence of the rheumatic diathesis implies a liability to dis turbance of the motor apparatus. The motor ganglia are an essen tial part of this apparatus. Those subject to rheumatism are, there fore, cceteris paribus more likely to have susceptible motor centres than those who are not. Thus the rheumatic diathesis predisposes to chorea. So much physiology teaches. But the practical questions still remaih—How is the chorea induced; what is its exciting cause; and why does it occur only in a small percentage of the total number of rheumatic subjects? Here, as is the case with delirium and nervous symptoms generally, constitutional predisposition plays an important part. The motor centres, like all other parts of the nervous system, are more suscep tible and more liable to disturbance in females than in males, and in young people than in those of more mature years. We accordingly find that it is in females and in young people that choreic symptoms are most apt to show themselves. The rheumatic constitution is by no means necessary to their production. A fright, or nervous shock, gastric or uterine derangement, may give rise to chorea and be the exciting cause of the disease in persons in whom there is no history of rheumatism. But many cases there are—so many that the connec
tion is too striking to have escaped detection—in which a present or prior rheumatic attack, with or without heart affection, is the only cause to which the chorea can be traced. Many cases there are, too, in which a rheumatic family history forms the only noteworthy feature.
In discussing the pathology of rheumatic chorea, we thus have two different classes of cases to deal with—those in which the chorea occurs either in connection with, or subsequent to, a rheumatic attack; and those in which there is only a family history of rheu matism.
A rheumatic attack means inflammation of an essential and im portant part of the motor apparatus and general disturbance of the whole system. If a nervous shock, or derangement of the digestive or uterine organs, may induce chorea in one predisposed to it, a rheumatic attack or an endocarditis may almost certainly do so too; for general rheumatic disturbance of the motor apparatus cannot but be regarded as a possible cause of disturbance of the motor centres. Thus the rheumatic diathesis may be the predisposing and the rheu matic attack the exciting cause of an attack of chorea. The combina tion of these two causes in the same subject suffices to explain the special tendency of chorea to occur in those who have suffered from rheumatism. The heart complications, to which the choreic phe nomena are by some ascribed, are a mere incidental accompaniment of the disease. They may, of course, act as an exciting cause in the same way as the joint affection or derangement of the uterine organs may, but they are not essential to the production of chorea.
But the predisposing cause may exist without the exciting. There may be a family predisposition to rheumatism, without the disease having ever occurred in a given member of the family. Choreic symptoms may show themselves in such a one any prior rheumatic attack, the exciting cause being some other disturbing agency, such as shock or gastric or uterine disturbance. No matter what the exciting cause, the disease is fitly described as one of rheu matic chorea, if what tended to its production, and predisposed to its existence, was the rheumatic constitution of the individual.
In a rheumatic subject predisposed to chorea through a suscep tible condition of the motor centres, it is an accident whether the chorea, when it does occur, comes on in connection with a rheumatic attack, subsequently to it, or prior to and independently of it. The ultimate pathological explanation of the relation of the rheumatism and the chorea is the same in each; the one disease consists in dis turbance of the peripheral portion of the motor apparatus of the body ; the other consists in disturbance of the motor centres.
In persons with susceptible and easily disturbed motor centres chorea may be induced by causes which would not give rise to it in others. The motor centres are most easily disturbed in people of rheumatic constitution because rheumatism is essentially a disease of the parts of the body over which the motor centres preside. Other morbid conditions, gout and rheumatoid arthritis, also affect the motor apparatus, without disturbing the motor centres ; but then they occur at an age at which chorea does not manifest itself. Chorea is essentially a disease of youth—so is rheumatism; it is the only joint trouble which is so.