In the other two chief forms we have a history of past syphilis or a senile sub ject usually advanced in years to give us a distinct clue. Here prolonged and wavering prodromata, especially if dif fuse or scattering and not focal, strongly suggest thrombosis. There are fre quently such warnings and forerunners of various kinds. Transitory parwsthe sim (tinglings, numbness, etc.), pareses, aphasic spells, twitchings, headaches, visual obscurations, cardiac and respira tory irregularities, lapses of memory, mental hebetude, dizziness, etc., accord ing to the location and extent of the threatened area, are more or less fre quent. If unilateral in type, they are the more in evidence. These, at times, last over a period of weeks or months, but often are of a few days' or less duration. "The physiologically-recurring waves of vessel-contraction and diurnal or other periods of fall in blood-pressure, added to the pathological narrowing of the ves sel (where there is danger of thrombosis) may evidently, for a time, limit the nour ishment of the respective area sufficiently to impair its function without actually causing necrosis. The tissues are still supplied with enough to keep them alive, and as soon as the flow again increases these resume their functions. Presently, however, if relief is not obtained, the matter goes too far, and irreparable soft ening ensues." In some of these cases conditions of astasia-abasia, dyslexia, etc., are noticeable. In reading, writing, muscular or other effort there is a quick tiring of function. "The centres act nor mally for a brief period, then fag out." This may apply to large areas or almost the whole brain, again is more one-sided or even further limited.
Some authorities claim that the spe cific form is usually limited to a single vessel or a few branches, and hence is focal in character, but to this there are certainly many exceptions. In the senile type, however, the process is widely dis tributed, and hence the manifestations are more general and diffuse. This ap plies more especially to the prodromata and general features than to the symp toms following the softening,—which latter necessarily represent one or more distinct foci.
"In the specific form, which may occur at almost any period of life, there may, or oftener may not, be much headache; if especially nocturnal, so much the more in evidence." Ophthalmologists recog nize a chorioretinitis syphilitica as anal ogous to specific diseases of the brain arteries. In suspected cases lacking a definite history of syphilis, a careful search must be made for any marks about the body or other indications pointing or not to that diagnosis.
Etiology. — Certain general influences play a secondary role. All debilitating and wasting diseases, by weakening the circulatory force and by reduction of the traversing fluid, have such a tendency. Excessively warm weather, a rapid rise in the atmospheric temperature, and marked fall of the barometric pressure favor the occurrence of thrombosis, while opposed to cerebral luemorrhage. Senil
ity also acts in the same sense, as well as in a more direct manner.
The more immediate causes fall under two heads: 1. Local disease of the vessel-walls. Atheroma, pre-eminently a disease of the old and favored by chronic alcoholism, occupies a prominent place here. It nar rows the lumen of the vessel, but may also be the object around which the thrombus starts. Syphilis acts essentially by thickening of the arterial wall (endar teritis syphilitica, periartcritis nodosa, etc.); it is said to cause thrombosis chiefly in those between twenty and fifty years of age.
Sometimes the thrombosis starts in an aneurismatically-dilated artery.
2. It may be due to a strong tendency of the blood to clot (leucocytosis often present). This is a much less frequent cause. Gout, chlorosis, and especially the puerperium (when the vessels of the uterus have to be closed by clot) here play a role. In such case a practically spontaneous coagulation occurs and ob structs an otherwise healthy vessel.
Pathology.—This is, from a practical stand-point, simple, and corresponds closely to that of embolism. Inasmuch, however, as the remaining vessels are so often more or less similarly diseased in the common forms, the chances of estab lishing an adequate collateral circulation are not as favorable. Consequently the area of softening, for any given vessel, is rather larger. So soon as the current has been entirely cut off for a short time, a few hours or probably less, necrosis is established and the part thus affected is hopelessly lost. The later course of such a focus is the same as that after embo lism.
Prognosis. — This has reference to three points: 1. The prodromal stage. Where it is possible to make the diagnosis and insti tute treatment at. this stage, softening can usually be headed off. This is quite intelligible in syphilis, though there is a great tendency to recurrence. And even if the specific process is absorbed, there remains ever after a weak spot in the arterial parietes that may under strain give way and be the source of a haemor rhage. The senile gouty and atheroma tous forms are also amenable, and not in frequently seem to recover permanently. Of course, in that happy event it is not to be supposed that the artery-wall is re juvenated, but only that things have so adjusted themselves that there are no longer active manifestations.
2. The thrombotic softening. This in itself is, as above stated, somewhat less favorable than in embolism. The tissue loss is permanent, and function can be compensated only to a degree.
3. The tendency of the process to ex tend. It is difficult to be very explicit on this point. In many cases there is reason to think that numerous vessels are more or less affected by the same process and that the same dyscrasic cause con tinues, only that it reaches extremes in but one or two at a time. Unless very carefully managed, we may expect that sooner or later the clanger-limit will be reached in some of these.