In China, where there is practically no treatment for syphilis, luetic ulcerations are exceedingly common and it has been suggested that insufficient treatment cures the skin lesions but adds to the effects on the nervous system. It will be remembered that skin and nerve tissue arise from similar embryological layers (epiblast) hence a suppression of toxic effect on one tissue may add to the burden on the other. It has been suggested that if the surface lesions are allowed to develop to maturity, the skin, which is the great elaborating center for antibodies, will produce enough adequately to protect the whole body; whereas, if the surface lesions are aborted, there is a diminished stimulus with consequent diminished elaboration of protective bodies. The brain is then liable to parenchymal invasion, since chemicals, owing to difference in their physical properties, cannot replace natural antibodies in controlling the disease in this location. This theory takes no reckoning of differences exhibited by variant strains of treponema in their tendencies toward selective localization. It has been noted that the form of syphilis endemic in certain regions is much less virulent than is the cosmopolitan form.
Pellagra.—Very important in diagnosis is a more or less prolonged prodromal period of neurasthenia which is apt to be more marked in the winter at a time when the skin and alimentary tract manifestations are in abeyance. Along with the anxiety and unrest of this neurasthenia we have lack of mental concentration and depression of spirits.
A melancholic state is almost always present in the psychosis of pellagra. There is not the indifferent, satisfied, more or less happy mental state of the case of general paresis. Some consider the pellagrous psychosis to belong to the toxic group, as from alcohol or cocaine, while others place it in the group of infective psychoses, as the post-influenzal one. Gregor regards it as belonging to the infective-exhaustive group. The insanity of pellagra is that of an acute confusional one.
In the final cachexia there is a dementia.
Sleeping Sickness.—It may be many months or even years before the mental changes follow the trypanosome fever stage. At first a change in disposition is noted, the patient becoming listless and apathetic.
There is great impairment of mental concentration and memory. There may be later on catatonic manifestations as echolalia, mutism or flexibilitas cerea. There may at times be paranoid manifestations to be succeeded by states of profound melancholia. In the terminal stage a comatose state overshadows the psychical manifestations.
Malaria.—Leaving out of account the acute delirious states which accompany cerebral malaria there have been reported cases showing various manifestations of psychic disturbances even to maniacal or melancholic forms of insanity.
It is a common practice to attribute the irritability and lack of mental concentration of those who have lived for a long time in the tropics to the damage done the cerebral cortex by the malarial parasite. It is certainly more reasonable to attribute these minor psychic disturbances to malaria rather than to actinic rays of the sun.
There is no doubt but that quinine, given either for treatment or prophylaxis of malaria, is a cause as potent as alcohol and tobacco in tropical neurasthenia.
Insolation.—It is popular to assign neurasthenic manifestations to the actinic rays of the sun or the tropical heat, as these influences operate on every resident of the tropics. It is very necessary to exclude derangements of the digestion due to errors in diet with resulting exhaustion of the pancreatic and hepatic functions.