Definition.—An inflammation of the pia and arachnoid membranes of the brain.
Etiology.—This is generally, if not always, a secondary lesion, the most frequent primary lesion being disease of the sinuses, the nose, or the middle ear. Being strictly an infectious disease, a great variety of bacteria have been found, besides the staphylococci and streptococci, those peculiar to the infectious fevers in general, but especially pneumonia, influenza, erysipelas, enteric fever, measles, scarlet fever, endocarditis, septicemia, diphtheria, and tuberculosis. Of the more chronic diseases that may precede it, may be mentioned Bright's disease, rheumatism, arteriosclerosis, and gout.
The disease is found more frequently between the ages of thirty and fifty, though when due to tuberculosis it is most common in children.
Pathology.—The locality, extent, and degree of tissue-changes vary; thus if due to middle-ear disease, the lesion will be unilateral and over the temporo-sphenoidal lobe; if due to pneumonia, endocarditis, or any infectious disease, the process will generally be bilateral and limited to the cortex, while at times the base alone is involved. The exudate varies from a fibrous exudate to a purulent or hemorrhagic infiltrate. The ventricles may be dilated, especially in children, and contain a turbulent fluid. When the exudate becomes purulent, the various microorganisms peculiar to septic processes and infectious diseases, are found in the fluid.
Symptoms.—These naturally vary, depending upon the location of the lesion, the extent of the inflammatory process, and the producing cause. When due to middle-ear lesions, the symptoms are those of well-defined meningitis, either tubercular or those of the epidemic form.
If the meningitis be a complication of any of the severe infectious diseases, the symptoms of the primary disease may obscure those of the local affection.
In the greater number of cases, however, there will be a train of symptoms quite characteristic. Headache, severe and protracted, is always present; delirium, followed by coma,, soon appears in many cases. The pulse is often slow, though in children it may be very rapid. Vomiting is present in a great many cases.
Photosbabia, intolerance to sound or irritation of the head, are seen in all severe types. Where the base is involved, the cranial nerves are affected, and strabismus, ptosis, or facial paralysis follow, and if the fifth nerve be involved, trophic changes are common symptoms. As the disease progresses, the spine becomes rigid, there is great retraction of the head, and opisthotonos may be pronounced. Convulsions, in children of nervous temperament, are apt to occur.
The suppurative process is announced by chills, and fever of an irregular or septic type.
Diagnosis.—The primary affection may so obscure the meningeal lesion for a few days as to make an early diagnosis quite difficult, if not impossible; sooner or later, however, characteristic symptoms develop, and there should be few mistakes as to the disease.
We must differentiate the tubercular from the non-tubercular form, and, if attention be paid to the following well-marked characteristics of the tubercular type, the difference can be readily seen. In tubercular meningitis there is a history of tuberculosis and the forming stage is of long duration. There is no apparent cause for the meningeal lesion. Generally there is the presence of tuberculosis in the lungs, and the meningeal lesion runs a more protracted course.
Prognosis.—Although a grave disease, it is not necessarily fatal.
Treatment.—The treatment does not differ materially from that used in epidemic cerebro-spinal meningitis. When due to middle-ear disease, operative measures afford some relief, and pave the way to recovery.