Acute pyogenic (bacterial) meningitis. Subacute and chronic meningitis.
- Meningitis is inflammation of the meninges.
- The meninges are 3 layers; dura mater, arachnoid mater and pia mater.
- Acute pyogenic meningitis is an inflammatory response to bacterial infection involving the pia and arachnoid membranes covering the brain and spinal cord.
The most common causative organisms:
- Streptoccoccus pneumoniae
- Neisseria meningitides
- Haemophilus influenza
Bacteria can spread to the meninges through:
- Local tissue invasion; hematogeneous seeding to the subarachnoid space
- Directly
- In children; upper respiratory tract, umbilical cord
Once the organisms cross the blood-brain barrier, they transfer into the CSF, which becomes cloudy and milky in appearance. The bacteria release endotoxins and provoke inflammatory reaction.
Clinical features
Symptoms and signs of meningitis show marked variation with age.
- Neonates – high temperature, bradycardia, cyanosis, diarrhea
- Infants – fever in afternoon/evening, poor feeding, vomiting, lack of response to stimulation
- Children – rapid onset of fever, headache, vomiting, progressive changes in mental status
- Adults
- Acute onset – most patient present to emergency center < 24 hours after onset.
- Headache, fever, neck stiffness, nausea, vomiting, clouding of consciousness, seizures, myoclonus, respiratory difficulties that often require intubation, hemiparesis or focal cranial nerve deficit. Papilledema is rare and suggests abscessus, empyema or VS thrombosis
- Kernig (we attempt to extend the patient’s lower limb when the hip is flexed) and Brudzinski signs (positive if flexion of the patient’s neck produces flexion in both legs and thighs) - their absence never rules out the diagnosis
- Older patients – fever and nuchal rigidity
Diagnosis
- CT and MRI - neither show abnormality in early stages. Main reason for imaging is to exclude other causes of headache, focal neurological signs or papilledema
- Peripheral blood may reveal polymorphonuclear leukocytosis from systemic infection or leukopenia caused by immunosuppression. Causative organism cultured from the blood.
- Lumbar puncture – only absolute means of diagnosing meningitis.
- CSF is cloudy and organisms are present in a direct smear.
- There is marked pleocytosis (white cell count - usually 1000-10 000/m³) with neutrophil predominance in the early stages, followed by a gradual increase of mononuclear cells
- The CSF glucose is usually less than 40 mg/dl (2.22 mmol/l).
- CSF protein is elevated and higher than 45 mg/dl
- CSF pressure elevated
- Gram-stained smears of CSF identify the causative organism. CSF culture provides a definitive diagnosis and allows determination of antibiotic sensitivity.
- Polymerase chain reaction has been used with CSF specimens to identify the etiologic agent in bacterial meningitis.