Meningitis is an infection the lining of the brain. If caused by bacteria, it’s rapidly fatal, but treatable if diagnosed in time. Viral meningitis is usually less serious, & with most viruses, it gets better on its own. Other germs like fungi fall in between, often fatal but not immediately, and often treatable. See Germs: Differences Among Them.
Adults with meningitis always have fevers, a stiff neck, & maybe mental changes. Lots of illnesses cause fever & headache, but with bacterial meningitis, a patient’s is so severe that they’re unable to bend their necks forward (like looking at their belly-button).
If we even think this might possibly be the diagnosis, we sent patients right to the ER, usually by ambulance. If transport will be at all delayed, we draw blood for a blood culture (to try to identify the germ eventually), and give a shot of antibiotic.
In the ER, they’ll do a spinal tap to find the exact germ, and give several antibiotics IV while waiting for results. They may admit the patient to the hospital, since a culture can take 2-3 days to identify both the germ, and the best antibiotic for that particular strain. If in the end it all looks like viral meningitis, and the patient is getting better, they’ll go home just fine.
Encephalitis is an infection of the brain tissue itself. It’s caused by a variety of viruses, some bacteria (syphilis, TB, etc.), protozoa (including malaria), cancer metastases, etc. etc.
It may cause a headache, but its main symptoms are fever and confusion. There can be stroke-like symptoms such as slurred speech, partial paralysis, personality changes, etc.
Such patients are sent by ambulance to an ER. Many tests will be done, like CT scan, MRI, spinal tap, blood tests, and more. The most urgent treatable cause of encephalitis is Herpes type-1 (cold-sore virus, not the STD), so patients receive that antiviral medicine plus antibiotics for bacteria while the cause is figured out. Depending on the cause, most patients recover well, but a number die or suffer permanent brain damage.
The term “encephalopathy” refers to conditions that cause confusion and act like encephalitis, but are not due to infections. It may be due to liver failure, alcoholism, toxins, medications, and more.
Brain Abscesses are caused by bacteria. They are diagnosed by CT scan, which is done if a patient with headache has abnormalities like those of either meningitis or encephalitis.