Acute Bacterial Meningitis, Meningococcal Meningitis, Subacute Meningitis, Recurrent meningitis
What is Meningitis?
Meningitis is inflammation of the membranes covering the spinal cord and brain (meninges) caused by bacterial, viral, or fungal infections. There are a number of types of meningitis.
- Acute bacterial meningitis is caused by bacteria spread from an infection in another part of the body such as the lung, ear, nose, throat or sinus. One bacterial strain (meningococcus) spreads quickly within relatively confined environments such as boarding schools or military bases and can cause local epidemics. This type of meningitis is considered to be a medical emergency as it can be lethal in hours if not diagnosed and treated promptly. Affecting up to 5,000 people each year in the US, about three-quarters of all cases of meningococcal meningitis occur before the age of ten.
- Aseptic meningitis is an inflammatory reaction of the meninges not caused by bacteria. It is most commonly caused by certain viruses, but can also be a reaction to certain medications or cells that are not normally present in the cerebrospinal fluid.
- Subacute meningitis can be caused by fungal infections, the spread (dissemination) of malignant cells, tuberculous organisms, or syphilis. In this form of meningitis, the symptoms evolve over a period of weeks.
- Recurrent meningitis is an infection that returns. It is usually due to a sinus defect that opens a pathway allowing organisms to penetrate the central nervous system.
How is it diagnosed?
Meningitis signs and symptoms
- A respiratory illness or sore throat often precedes the fever, headache, stiff neck and vomiting that characterize acute meningitis. In older children or adults, changes in consciousness progress through irritability, confusion, drowsiness, stupor, and coma.
- In meningococcal meningitis, the symptoms develop rapidly. Adults may become desperately ill within 24 hours. The course can be even shorter in children.
- The symptoms of viral meningitis may be milder, resembling influenza.
- Tuberculous meningitis progresses much more slowly. The individual may be sick for several weeks before the typical meningitis symptoms develop.
Physical exam includes inspecting the head, ears, and skin for the source of infection. Abrupt neck flexion (bending towards chest) with the individual lying on his back, causes an involuntary flexion of the knees (positive Brudzinski's sign). Attempts to extend the knee from the flexed-thigh position are met with pain and reflex contraction (positive Kernig's sign).
Tests: Lumbar puncture is performed without delay. The cerebrospinal fluid is analyzed for increased pressure, protein and glucose content, and white blood cells (leukocytes). Search for an infectious source may also include cultures of blood, nose and throat (nasopharynx), respiratory secretions, urine, and any skin lesion. Laboratory analysis of the blood usually includes a complete blood cell count (CBC) and glucose level. A depressed glucose level (less than 50% of the blood glucose) is common in bacterial, tuberculous, and fungal meningitis, but is unusual in viral meningitis. A CT scan may be normal or it may show evidence of sinus or mastoid infection, skull fracture or congenital anomalies.
How is Meningitis treated?
If the diagnosis is acute bacterial meningitis, antibiotic drug therapy is started immediately. Choice of antibiotics depends on the type of bacteria causing the infection. In some cases, treatment for brain swelling, shock, convulsions, or dehydration may also be needed. Treatment of aseptic meningitis is directed at pain relief (analgesics) and fever reduction. Treatment of subacute meningitis varies depending on the cause of the disease (fungus, tuberculosis, syphilis). In recurrent meningitis, drainage of infected sinuses or mastoids may be necessary.
What might complicate it?
Possible complications include seizures, shock, deafness, dehydration, and lower cranial nerve palsies. Fluid leaking into the membrane covering the brain (subdural effusion) can cause swelling in the brain (cerebral edema, hydrocephalus). A localized infection (cerebral abscess) can form in the brain. Even with antibiotic treatment, meningitis can be fatal.
Prognosis depends on the causative organism and the severity of the illness. In most cases, recovery is possible with prompt and appropriate treatment. However, in some cases, brain damage may occur. Underlying conditions such as being on immunosuppressant medications, cancer (malignancy), HIV infection, and alcoholism worsen the prognosis.
Differential diagnoses include subarachnoid hemorrhage, bacterial endocarditis, malignant hypertension, lead poisoning, porphyria, migraine, viral encephalitis, cerebral abscesses, cerebral tumor, and subdural hematoma.
Neurologist and infectious disease specialist.
Last updated 17 November 2011