In this connection it is proper to mention tremor mercurialis and tremor saturninus, which might possibly lead to mistake should proper attention not be paid to the history and to the symptoms. Paul51 reports a case of the former affection, and gives a specimen of the handwriting of the patient.
51 C. Paul, Bull. et Mém. de la Soc. de Thérap., Paris, 1881, xiii. pp. 129-131.
Traumatisms, etc. of the various nerves of the arm usually interfere with the proper play of the muscles supplied by them, and although certain of the milder forms of inflammation or of congestion, as previously mentioned, are sometimes present in cases of copodyscinesia, it is manifestly improper to include all cases of impairment of hand-and-arm movement from nerve-injury under this head.
Palsy from pressure, as from sleeping with the head resting upon the arm or with the arm hanging over the back of a chair, is a frequent cause of paresis or paralysis of the muscles supplied by the musculo-spiral.
Tumors pressing upon the nerves in any part of their course, or neuromata, may be mentioned among the more ordinary affections that possibly might mislead.
Tenosynovitis which is described by Hopkins52 as a congestion of the tendinous sheaths in the forearm, with insufficient lubrication of the same, causing pain and interfering with motion, might be mistaken for the disease in question, especially as it occurs in many of the same occupations which furnish cases of copodyscinesia.
52 Wm. Barton Hopkins, “Tenosynovitis,” Med. News, Philada., July 15, 1882.
The exciting cause of tenosynovitis is “usually the resumption of work to which the individual is thoroughly accustomed after a shorter or longer interval when he is out of practice,” and not the monotonous repetition of the same act. The differential diagnosis should occasion no difficulty, as there is soreness amounting to positive pain upon motion or pressure along the course of the affected tendons, and the peculiar creaking which is communicated to the finger on palpation.
PATHOLOGY AND MORBID ANATOMY.—Unfortunately for correct determination of the pathological conditions underlying these neuroses, there have been no reported examinations of the spinal cord and nerves in subjects affected with copodyscinesia dying from intercurrent diseases, although it is probable that no macroscopic lesion would be discovered.
Solly53 reports the post-mortem appearance in a case of impaired writing-power in which he found a granular disintegration of the cervical portion of the cord; but this case, from his description, was evidently one in which the impairment of power was merely one of the numerous symptoms dependent upon disease of the cervical cord from degenerative changes, and not a true case of writers' cramp. If such a condition underlaid these neuroses, the cures occasionally reported and the relief frequently felt after the use of the galvanic current could not be explained.