What is Meningitis?
Meningitis is the physical condition of the meninges, three tissue layers in charge of protecting the brain and spinal cord. What makes meningitis so threatening compared to other diseases is the sheer speed with which it attacks a person’s body. In most cases, it causes death within a day.
More specifically, it refers to the inflammation of the two inner layers which are called the leptomeninges.
The outer layer of the meninges is the dura mater, the middle layer is the arachnoid mater, and the inner layer is the pia mater. These last two, the arachnoid and pia maters,
are the leptomeninges.
Between the leptomeninges, there’s the subarachnoid space, which houses a cerebrospinal fluid, or CSF. CSF is a clear, watery liquid which is pumped around the spinal cord and brain, cushioning them from impact and bathing them in nutrients.
Types of Meningitis.
The disease primarily comes in three forms: fungal, viral and bacterial.
Meningitis is the inflammation of the leptomeninges, which remembers the inner two membranes around the brain and spinal cord. It is not the inflammation of the brain itself, that’s encephalitis, but sometimes they can occur together and when that happens it’s called meningoencephalitis.
So meningitis needs some kind of trigger for the inflammation and could be an autoimmune disease, where the body attacks itself, like lupus, or the body having an adverse reaction to some medication, which can happen with intrathecal therapy, when medication is injected directly into the CSF.
But, by far, infection is the most common trigger for meningitis across all age groups, like with the Neisseria meningitides bacteria or herpes simplex virus for example.
Now there are two routes that an infection takes to reach the CSF and leptomeninges. The first way is direct spread, which is when a pathogen gets inside the skull or spinal column, and then penetrates the meninges, eventually ending up in the CSF.
Sometimes the pathogen will have come through the overlying skin or up through the nose, but it’s more likely that there’s an anatomical defect to blame.
For example, it could be a congenital defect like spina bifida, or an acquired one like a skull fracture, where there might be CSF leaking through the sinuses.
The second way is hematogenous spread, which is when a pathogen enters the bloodstream and moves through the endothelial cells in the blood vessels making up the blood-brain barrier and gets into the CSF. To do this, the pathogens typically have to bind to surface receptors on the endothelial cells in order to get across.
Otherwise, they have to find areas of damage or more vulnerable spots like the choroid plexus. Once the pathogen finds a way into the CSF it can start multiplying.
Soon enough, the handful of white blood cells surveilling the CSF identify the pathogen and release cytokines to recruit additional immune cells.
Over time, a microliter of CSF might go on to contain up to thousands of white blood cells, but any more than five usually defines meningitis.
In most bacterial cases, there’ll be above 100 white blood cells per microliter, and more than 90% PMNs.
In most viral cases, there’ll be 10 to 1000 white blood cells; over 50% lymphocytes and under 20% PMNs.
In most fungal cases, there’ll be 10-500 white blood cells, with over being 50% lymphocytes.
In most cases of tuberculous meningitis there’ll be 50-500 white blood cells with over 80% being lymphocytes.
From there, bacteria have rapid access to the body’s tissues including a membrane called the blood-brain barrier. This is made of a tight mesh of cells which separate blood vessels from the brain and block everything except for a specific set of particles, including water molecules and some gasses. But in ways that scientists are still trying to understand, meningitis bacteria can trick the barrier into letting them through.
Symptoms of Meningitis.
meningitis symptoms are headaches, fevers, and nuchal rigidity, or neck stiffness. It can also cause photophobia which is discomfort with bright lights, or phonophobia, which is discomfort with loud noises. Meningoencephalitis can cause an altered mental state or seizures.
Common symptoms include:
Inability To Unbend Legs
Rigidity of Occipital Muscles
Stomachache, Nausea & Vomiting
The diagnosis of meningitis starts with a physical exam. One maneuver is when a person lies flat on their back facing upwards, and one of their legs is raised with the knee flexed to a 90-degree angle.
Then, the leg is supported and slowly straightened at the knee. If this causes back pain, then it’s called the Kernig’s sign. Another maneuver is when a person lies flat on their back facing upwards and has their neck supported and flexed.
If this causes them to automatically flex their knees or hips, then it’s called the Brudzinski’s sign.
If meningitis is suspected, a lumbar puncture can be done. This is when a needle goes through the lower lumbar vertebral levels of the spinal cord, between L3 and L4 for example. The needle penetrates into the subarachnoid space and a few milliliters of CSF is taken.
The opening pressure can be measured, and the CSF can be analyzed for white blood cells, protein, and glucose. Polymerase chain reaction, or PCR, might be used to find Specific causes like HIV, enterovirus, HSV, or tuberculosis.
If a particular infection seems like an obvious cause, then a test for that might be used, like the Western blot for Borrelia burgdorferi bacteria, or a thin blood smear for malaria.
If you’re concerned that you or someone you know may have meningitis, get to the doctor as soon as possible; quick action could save your life.
Treatment of Meningitis.
The treatment of meningitis depends on the underlying cause. For bacterial meningitis, It’s common is to administer steroids and then antibiotics, to prevent massive injury to the leptomeninges from the inflammation caused as the antibiotics destroy the bacteria.
In general, the treatment – antivirals, antibacterials, antifungals, or antiparasitic drugs are aimed at the specific cause of meningitis.
Prevention with a vaccine is appropriate for some causes like Neisseria meningitidis, but also for mumps and for disseminated tuberculosis. Prophylactic antibiotics can also be administered, to avoid outbreaks of bacterial meningitis like in households where individuals haven’t been vaccinated against Neisseria meningitidis.