The pathogenesis of rheumatoid arthritis is the subject of differences of opinion very like those existing in regard to acute articular rheumatism. The weight of evidence is in favor of its diathetic relationship to rheumatism; and the doctrine of an arthritic diathesis and of the operation of the causes of the disease through the nervous system appears to be specially applicable to it, with less difficulty than to acute rheumatism, and the probability of a specific germ being its true cause is very remote. What seems to be necessary in addition to the preceding is, that the causes shall be more persisting and oft-recurring, so as to maintain a prolonged local irritation of the articular tissues, or that the neuro-arthritic diathesis shall be highly developed. Under these conditions the prolonged or oft-repeated application of cold and damp to the peripheral nerves, severe or oft-repeated slight injuries to joints, urethral or ovario-uterine irritation, chronic gout or rheumatism, or even, exceptionally, an attack of the acute form of these diseases, may originate rheumatoid arthritis; and all wearing influences, such as anæmia, excessive menstruation, prolonged lactation, innutrition, failing health, mental anxiety, or shock, etc., act as adjuvants in the development, aggravation, and maintenance of the articular disease.
DIAGNOSIS.—It is perhaps not possible to distinguish with certainty either the acute or the chronic form of rheumatoid arthritis from subacute or chronic rheumarthritis respectively before the characteristic deformities of the former affections have appeared. Acute rheumatoid arthritis, which is comparatively rare, may be said to exist, rather than subacute articular rheumatism, if the disease affect early and chiefly the smaller joints of the hands and feet alone or along with some of the larger articulations, especially the sterno-clavicular or the temporo-maxillary; if the effusion into the joints be abundant; if inflammation persist in the articulations first involved, notwithstanding the invasion of other joints; if the heart escape; if the patient be a female who is constitutionally delicate, or has borne children rapidly, or is the subject of disordered menstruation, or has been attacked soon after childbirth or during lactation;—finally, if, on cessation of the attack, one or more of the joints remain swollen and permanently enlarged and impaired in function. The coexistence of iritis, or a history of a previous attack of that disease not attributable to syphilis or gout, would strengthen the above view.
Precisely the same considerations serve to distinguish chronic general or polyarticular rheumatoid arthritis from chronic articular rheumatism, with the following qualifications: endo- or pericarditis is not of frequent occurrence in chronic rheumatism, so that this distinction is not available, and chronic rheumarthritis of long standing does sometimes impair the movements of the joints, and even produce slight alterations in them. However, it does not, as a rule, involve so many joints as rheumatoid arthritis; it is less symmetrical in its distribution, and much less prone to implicate the sterno-clavicular, the temporo-maxillary, or the vertebral articulations. Nor does it cause removal of the articular cartilage, enlargement of the heads of the bones, and the formation of osteophytes around them, and of loose bodies in the articulations, together with marked deformities and luxations of the joints. A history of a remote or recent attack of acute rheumarthritis or of chorea, or the presence of chronic valvular disease, would strongly indicate the simple rheumatic nature of the case.
The partial form of rheumatoid arthritis can with even less certainty than the general be distinguished from chronic articular rheumatism before the characteristic alterations of the joints have been developed, more especially as it is sometimes a consequence of gouty irritation and probably of chronic rheumatism. Chronic arthritis following a traumatic cause, and persisting obstinately in the injured joint is probably rheumatoid, if not strumous, gouty, or periarthritic.
But before definitely deciding it will be prudent to await the development of some of the characteristic alterations of structure appertaining to rheumatoid arthritis. An affection of the shoulder frequently occurs which resembles in many respects rheumatoid arthritis, and has been well described by Simon Duplay253 and W. Pepper.254 It usually follows an injury, such as contusion, sprain, etc., of the joint, but may be spontaneous; it is unattended by swelling or deformity. Its early symptoms are pain on pressure of the shoulder a little below the outer border of the acromion, and especially behind it and at the coracoid process, also about the insertion of the deltoid and below the acromion during movements of the joint, especially when the arm is raised from the side or rotated inwardly; early restriction of these movements, which increases till a fibrous ankylosis becomes established and scapula and humerus move together as one piece, motion between those bones no longer existing, and forcible attempts to produce it giving great pain, and sometimes producing crepitus in or about the articulation; sometimes early numbness and pain down the member to the hand in the course of the ulnar, internal cutaneous, or the radial nerve; vicious and painful semiflexion of the elbow; after a time wasting of the group of muscles which move the shoulder-joint. Although usually monoarticular and of traumatic origin, I have seen it affect first one and then the other shoulder in the absence of any known injury, and beginning like a neuritis or a neuralgia of the scapulo-humeral nerves. Duplay, however, regards it as a periarthritis. It may be distinguished from the rheumatoid arthritis by the absence of effusion into or enlargement of the articulation, and of deformity of the bones; by the early restriction of the movements and the rapid development of adhesions which fix the articulation; and by the curability of the disease.
253 Archives Générales de Méd., Nov., 1872, pp. 512-542.
254 Archives of Med., Oct., 1880.
The articular affection of locomotor ataxia sometimes closely resembles monoarticular rheumatoid arthritis,255 but may be distinguished by its sudden invasion, often without pain or fever; the prompt development of a general and often enormous tumefaction of the entire member, with copious effusion into the joint; the early destruction of the articular cartilages, the rapid wearing away of the heads of the bones, and the proneness to spontaneous fracture of their brittle shafts; the prompt absorption of the articular effusion, followed by a relaxed state of the ligaments and a facility of dislocation; the early occurrence of the articular affection, when motor inco-ordination is scarcely developed, and its frequent association with the crises of ataxia or the presence of some of the other symptoms of that disease. The importance of these facts will be especially evident in those examples of ataxic articular disease in which, at an advanced stage, eburnation and deformity of the articular surfaces, with the formation of loose bodies and osteophytes, are observed, just as they are in arthritis deformans.
255 Charcot's Lectures on Diseases of the Nervous System, Syd. Soc., 1877; Archives de Physiologie, t. i., p. 161, 1868; ibid., xi., 1869.
Articular disease closely allied to what occurs in locomotor ataxia is now and then observed in the early stages of progressive muscular atrophy,256 but while the large joints, more particularly the knee and the shoulder, suffer in the former affection, the phalangeal chiefly and the larger articulations more rarely are attacked in the latter. Of course the peculiar symptoms of progressive muscular atrophy coexisting with those of the articular affection would serve to distinguish the latter from rheumatoid arthritis.