PATHOPHYSIOLOGY: The causative organism enters the bloodstream, crosses the blood brain barrier, and triggers an inflammatory reaction in the meninges. The blood brain barrier Independent of the causative agent, inflammation of the subarachnoid and piamater occurs. Increased intracranial pressure (ICP) results. Meningeal infections generally originate in one of two ways: either through the bloodstream from other infections (cellulitis) or by direct extension (after a traumatic injury to the facial bones). Bacterial or meningococcal meningitis also occurs as an opportunistic infection in patients with acquired immunodeficiency syndrome (AIDS) and as a complication of Lyme disease. Bacterial meningitis is the most significant form. The common bacterial pathogens are; N. meningitidis (meningococcal meningitis) and S. pneumoniae, accounting for 80% of cases of meningitis in adults. Haemophilus influenzae was once a common cause of meningitis in children, but, because of vaccination, infection with this organism is now rare in developed countries. Streptococcus:
CLINICAL MANIFESTATIONS: Headache and fever are frequently the initial symptoms; fever tends to remain high throughout the course of the illness; the headache is usually either steady or throbbing and very severe as a result of meningeal irritation. Meningeal irritation results in a number of other wellrecognized signs common to all types of meningitis: Nuchal rigidity (stiff neck) is an early sign. Positive Kernig’s sign: When lying with thigh flexed on abdomen, patient cannot completely extend leg. Positive Brudzinski’s sign: Flexing patient’s neck produces flexion of the knees and hips; passive flexion of lower extremity of one side produces similar movement for opposite extremity. Photophobia (extreme sensitivity to light) is common. Rash (N. meningitidis): ranges from petechial rash with purpuric lesions to large areas of ecchymosis. Disorientation and memory impairment; behavioral manifestations are also common. As the illness progresses, lethargy, unresponsiveness, and coma may develop. Seizures can occur and are the result of areas of irritability in the brain; ICP increases secondary to diffuse brain swelling or hydrocephalus; initial signs of increased ICP include decreased level of consciousness and focal motor deficits. An acute fulminant infection occurs in about 10% of patients with meningococcal meningitis, producing signs of overwhelming septicemia: an abrupt onset of high fever, extensive purpuric lesions (over the face and extremities), shock, and signs of disseminated intravascular coagulation (DIC); death may occur within a few hours after onset of the infection.
ASSESSMENT AND DIAGNOSTIC FINDINGS: Computed tomography (CT) scan or magnetic resonance imaging (MRI) scan to detect a shift in brain contents (which may lead to herniation) prior to a lumbar puncture. Key diagnostic tests: bacterial culture and Gram staining of CSF and blood.
PREVENTION: The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention (CDC) (2008) recommends that the meningococcal conjugated vaccine be given to adolescents entering high school and to college freshmen living in dormitories. Vaccination should also be considered as an adjunct to antibiotic chemoprophylaxis for anyone living with a person who develops meningococcal infection. Vaccination against H. influenzae and S. pneumoniae should be encouraged for children and at-risk adults. People in close contact with patients with meningococcal meningitis should be treated with antimicrobial chemoprophylaxis using rifampin, ciprofloxacin hydrochloride (Cipro), or ceftriaxone sodium (Rocephin). Therapy should be started within 24 hours after exposure because a delay in the initiation of therapy limits the effectiveness of the prophylaxis.
MEDICAL MANAGEMENT: Vancomycin hydrochloride in combination with one of the cephalosporins (eg, ceftriaxone sodium, cefotaxime sodium) is administered by intravenous (IV) injection. Dexamethasone has been shown to be beneficial as adjunct therapy in the treatment of acute bacterial meningitis and in pneumococcal meningitis. Dehydration and shock are treated with fluid volume expanders. Seizures, which may occur early in the course of the disease, are controlled with phenytoin. Increased ICP is treated as necessary.
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