In all of these cases it will be seen how little we can rely upon any one pathog-nomonic sign, and that if we would avoid danger ous or even fatal errors in diagnosis, regard must be had to all that can be learned of altered function or action in disea.se.
§ 8. Chronic Disease.—If the diagnosis of acute diseases of the encephalon be beset with difficulties, those encountered in inves tigating states of chronic disease are still greater, and in the majority of cases it must be confessed that we can scarcely form any certain opinion as to the actual lesion; there we had to guard against being led by symptoms referable to the brain, to overlook acute diseases in other parts to which they were only secondary; here we are very apt to mistake mere functional disturbance for chronic disease. In a practical point of view, and this is the most important one, the only question of real interest is, whether we can distinguish such as are dependent on states of chronic inflammation, and therefore remegiable in a majority of cases, from those which depend upon other cases, when we must be content with treating symptoms ; because, in the absence of in flammation, the same broad and rational principles of treatment will be most efficacious, whether they depend upon functional disturbance or on serious disease.
The first inquiry is necessarily the history of their origin and progress; the next must be into the condition of all the other organs of the body, because there are none, it may be said, which do not occasionally react upon the brain; some, it is true, more constantly than others; indeed, very distinct classes of symptoms seem to be pretty constantly associated with particular forms of disease, while the coincidence in other cases is rather accidental.
If we fail to detect disease elsewhere, we must again revert to the brain itself, investigating more closely the relation of each phenomenon, and evidence of disease of bone must be sought for. The presence of inflammatory action is most clearly indicated when. the commencement of the attack can be traced back to a fixed and not very distant period, and when the symptoms follow a definite course; uncertainty with reference to their development and their irregularity or incongruity are to be taken rather as indications of insidious disease, or of nervous, hysterical, or hypo chondriical disorders. As in the acute forms, careful inquiry
must be made regarding previous injuries or accidents, and the presence of syphilitic nodes or tumors of the scalp; caries and suppuration rather excite acute than chronic inflammation, and, when associated with nervous symptoms of long standing, are more commonly found to have acted through the medium of the nerve-sheaths, than through the brain or it,s inve,sting tnem branes.
After careful investigation of the history of the case. the other attendant circumstances are to considered. A cachectic state which is not dependent on discoverable disease in other organs is, to a certain extent, presumptive proof of organic disease : its absence is, on the contrary, an argument in favor of chronic inflammation where disease of the brain is believed to exist. To this many exceptions are found; and encysted tumors, for example, frequently proceed to a fatal termination without any symptom of cachexia.
Headache more or less accompanies all chronic diseases of the brain ; much has been written on this subject, but little is known with certainty beyond the fact that cases resembling each other in their essence may differ very greatly in this respect, while those producing similar sensations of pain, weight, ach ing, or dizziness, may reveal after death lesions very unlike one another. It is most difficult to discriminate cases in which this symptom stands alone as evidence of disease of the brain, from those in which it is merely secondary on deranged digestion. When dyspepsia, vomiting or constipation coexists with headache, the determination must rather rest on the absence or presence of concomitant signs than on its intensity or duration : perhaps when dependent, on disease of the brain, the pain recurs more frequently, and without chylo poietic derangement ; the intermissions are less frequent, the paroxysms of longer duration ; it is aggravated by noise, motion, light, company, and is never dispelled, like a dyspeptic headache, by exercise or excitement. Very often, too, the recumbent posture aggravates the disorder ; but its significance is greatest when it is accompanied by any disturbance of the mental faculties, or disorder, however slight, in the performance of muscular movements.