MENINGITIS [Symptoms and Signs / Causes / Pathogenesis of Bacterial Meningitis / Complications]

                Bacterial meningitis is the most common and serious bacterial infection of the central nervous system (CNS), characterized by an acute purulent infection of the meninges around the brain and spinal cord (pia mater, arachnoid)and subarachnoid space Without prompt antibiotic treatment bacterial meningitis is serious, and can be fatal within days. Delayed treatment increases the risk of permanent brain damage or death Approximately 1.2 million cases are estimated to suffer from bacterial meningitis annually worldwide, resulting in 135,000 deaths.


The Meninges

The meninges comprise three membranes that, together with the cerebrospinal fluid, enclose and protect the brain and spinal cord. The pia mater is a very delicate impermeable membrane that firmly adheres to the surface of the brain. The arachnoid mater is a loosely fitting sac on top of the pia mater. The subarachnoid space separates the arachnoid and pia mater membranes and is filled with cerebrospinal fluid. The outermost membrane, the dura mater, is a thick durable membrane, which is attached to both the arachnoid membrane and the skull 



Symptoms and Signs

Early meningitis symptoms may mimic upper respiratory tract infection. Symptoms may develop over several hours or over a few days. Possible signs and symptoms in anyone older than the age of 2 include



*Sudden high fever

*Stiff neck

*Severe headache

* Headache with nausea or vomiting

* Confusion or difficulty concentrating

* Seizures

* Sleepiness or difficulty waking

* Photophobia (sensitivity to light)

* No appetite or thirst

*Skin rash (sometimes, such as in meningococcal meningitis).


Causes

1. Bacterial meningitis: Bacteria that enter the bloodstream and travel to the brain and spinal cord cause acute bacterial meningitis. Pneumococcus or meningococcus type of bacteria are causative organisms 

2. Viral meningitis: The symptoms of viral meningitis are same as in bacterial meningitis, but milder. Viral meningitis often clears on its own. In most cases. there is no specific treatment for viral meningitis. Most people who get mild viral meningitis usually recover completely in 7 to 10 days without treatment.

Since, bacterial meningitis is a serious disorder, it is important to differentiate from viral meningitis. One of the tests for this differentiation is the physical appearance, chemical analysis and microscopic examination of cerebrospinal fluid (CSF) obtained by lumbar puncture in the patient. The CSF in bacterial meningitis is characterised by being turbid in appearance, decreased glucose concentration, increase protein concentration and large number of white blood cells, chiefly neutrophils. The CSF in viral meningitis is clear in appearance, normal sugar concentration, only mild increase in protein concentration and lesser number of white blood cells, chiefly lymphocytes

Microscopic Appearance of CSF in Viral meningitis 

                         Microscopic Appearance of CSF in bacterial meningitis

Pathogenesis of Bacterial Meningitis

In most of the cases, the disorder starts with a viral upper respiratory infection which breaks down the protective barrier provided by the mucous membrane of the nasal cavity. As a result, bacteria that normally reside on the nasal mucous membrane are able to enter the blood stream. Once bacteria have entered the bloodstream, they enter the subarachnoid space in places where the blood-brain barrier is relatively weak, i.e. the choroid plexus.

                The cerebrospinal fluid present in the subarachnoid space is an ideal medium for proliferation of bacteria because it has enough nutrients and very few phagocytic cells. Cells of the innate immune system of CNS (microglia and astrocytes) located in the choroid plexus and ependyma, detect bacteria and secrete cytokinesis chemokines which attract circulating granulocytes into CSF. Granulocytes and macrophages contain powerful lysosomal enzymes used to kill the bacteria, but these cells have short lifespan. On senescence, these cells release proteolytic enzymes into cerebral interstitial space and damage the brain tissue and blood vessels (vasculitis). So the brain damage in bacterial meningitis is partly due to bacteria and partly by inflammatory response. The most dangerous complication of bacterial meningitis is increased intracranial pressure from cerebral edema. Cerebral edema results from greater permeability of blood-brain barrier, increased cerebral hypoxia and cellular toxicity. Increased intracranial pressure, in turn, causes decreased cerebral perfusion, ischemia, hypoxia and neuronal necrosis 

Meningitis complications can be severe. The longer the delay in start of treatment, greater is the brain damage and other complications, including:

Complication

* Hearing loss.

* Ataxia.

* Cortical blindness.

* Mental retardation.

* Other cranial nerve dysfunction.

* Kidney failure

* Death

* Paralysis.

* Muscular hypertonia.

* Death.