3. The muscular atrophy which follows joint lesions is of reflex origin, and is due to purely dynamic alterations in the cord, since no anatomical lesion of the anterior cornua or peripheral nerves is found.
These results support the views advanced by Paget, Charcot, and others as to the reflex nature of the changes, and Gowers" regards such a theory as the only tenable one. He adds : "It is, however, an interesting fact that the wasting is accompanied by an increase in the myotatic irritability. 'We have in fact the condition that often re sults from slight degeneration of the pyramidal tracts, and must be immediately due to the changes in the terminations of the pyramidal fibres in the gray matter—increased myotatic irritability and slight wasting, and merely a slight diminution in the electrical irritability, similar to each current." The atrophy of arthritis deformans resembles that connected with other joint affections in tending to affect the extensors more than the flexors, although both sets of muscles may share in the atrophy, but in some cases the wasting is extreme and some of the affected muscles occasionally yield even the complete reaction of degeneration.
These facts are among those relied upon by authors who maintain the primary nature of the muscular atrophy in this disease, and who further maintain that the atrophy may have a wider distribution then the joint lesions, affecting limbs or portions of limbs in which the joints are as yet intact.
It is possible and indeed probable that in arthritis deformans we have superadded to the reflex atrophy a primary muscular affection similar to the dystrophy of the skin which is not infrequently ob served, but this would not account for the whole of the atrophy, since we cannot suppose that such a joint disease as arthritis deformans will not share with all other joint diseases the tendency to produce a reflex atrophy. It is certainly the rule that the atrophy follows rather than precedes the joint lesions, but it is an interesting fact which per haps lends support to the idea of a mixed atrophy, that although in crease of myotatic irritability is often observed, it is by no means constant in limbs affected by arthritis deformans, even when its absence cannot be explained by the condition of the joints.
Sometimes the stiffness or painful condition of the joints prevents the examination of the reflexes, but this is not often the case.
Some years ago I examined the condition of the supinator, triceps, and knee jerks in fifty patients suffering from arthritis deformans, and the results may be summed up as follows : Among 23 cases which exhibited well-marked muscular atrophy, there were 18 in which increase of some of the reflexes was observed; whereas in 27 cases in which the atrophy was comparatively slight there was increase of reflexes in 14 only.
As iu other varieties of arthritic muscular atrophy the increase of my (Antic irritability is not always confined to the affected limb. In cases in which one hip-joint is alone affected both knee jerks may he increased. In some cases the increase is very conspicuous. Thus a man aged thirty-two years had all the reflexes greatly exaggerated. His hands, feet, elbows, knees, shoulders, and ankles were all the seats of arthritis deformans of a severe type. A tap upon either supinator tendon caused contraction of the triceps and some clothe spasm, and when the triceps tendon was struck clonus was again produced and contractions of all the arm and scapular muscles. There was also conspicuous exaggeration of the knee jerks, with slight foot clonus on the left side. The muscles exhibited conspicuous atrophy and the muscular deformities were considerable. A somewhat similar case, in which a tap upon the patella or triceps tendon not only produced a greatly exaggerated jerk, but also gave rise to contraction of the trunk muscles, has been recorded by Mader" of Vienna.
Occasionally mere extension of a limb Serves to set up a clonic spasm.
Muscula)• Contracture as a Cause of Deformities.—Spasmodic con tracture of the affected muscles plays a very important and conspicu ous part in the production of the deformities met with iu severe and long-standing cases of arthritis deformans.