GENERAL ETIOLOGY.—We do not know why in any individual case syphilis selects one portion of the nervous centres rather than another for attack; indeed, it is only rarely that any exciting cause can be discovered.
It is not unnatural to expect that any agency which is capable of exciting an inflammation of a nerve-centre may, when present in a syphilitic person, provoke a specific disease of such centre. Thus, thermic fever is a very common cause of chronic meningitis, and in the Journ. de Méd. et Chir. (Paris, 1879, p. 191) a case is reported in which cerebral syphilis followed a sunstroke; I have myself seen one similar instance, and in Roberts's case of precocious cerebral syphilis (see p. 804) the first convulsion came whilst the man was fishing on a very hot day, and may have been precipitated by the exposure.
Blows and other traumatisms would be expected to figure largely as exciting causes of nervous syphilis, but they, in fact, are only rarely present. I have seen one or two cases of specific brain disease attributed to violence by the patient, and several cases of possibly specific spinal disease—one in which a poliomyelitis followed a fall on the ice; one in which, after a fall from a cart and marked spinal concussion, a local myelitis developed;1 and one of a general myelitis following an injury by a horse. The only records of such cases are those of Broadbent2 and those collected by Heubner.3
1 Univers. Hosp. Dispen. Service-Book, x., 1875, p. 58.
2 Lond. Lancet, 1876, ii. p. 741.
3 Ziemssen's Encyclopædia, xii. 301.
Various authorities attach much influence to over-study and other forms of cerebral strain in exciting brain syphilis. Engelstedt is stated to have reported cases having such etiological relations, and Fournier4 affirms that he has especially seen the disease in professional men and other persons habitually exercising their brains to excess. Neither in private nor public practice have I met with an instance where over-brainwork could be considered a distinct etiological factor, whilst I have seen some hundreds of cases from amongst the laboring classes, in whom the intellectual faculties are chiefly dormant.
4 La Syphilis du Cerveau.
The drift of the evidence in medical literature is so pronounced, and so in accord with my own experience, that I believe it may be positively affirmed that in the vast majority of cases of nervous syphilis no exciting cause can be found.
Inherited syphilis seems to be less prone than the acquired diathesis to attack the nervous system, but is certainly capable of so acting. As early as 1779, Joseph Glenck5 reported a case of a girl, six years old, cured by a mercurial course of an epilepsy of three years' standing and of other manifestations of hereditary syphilis. Graefe found gummatous tumors in the cerebrum of a child nearly two years old.6 O. Huebner7 details the occurrence of pachymeningitis hæmorrhagica in a syphilitic infant under a year old. Hans Chiari8 reports a case in which very pronounced syphilitic degeneration of the brain-vessels was found in a child fourteen months old. Both Barlow9 and T. S. Dowse10 report cases of nerve syphilis in male infants of fifteen months. For other similar cases the reader is referred to an article by J. Parrott,11 and to a paper by M. E. Troisier.12