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Meningitis is the most common case asked in almost
all USMLE exams
A Case of Bacterial Meningitis Bacterial meningitis affects 1 in 500 children younger than 2 years. Meningitis most commonly presents with subtle signs and symptoms that may easily be mistaken for a benign childhood illness.
In older infants and children, initial symptoms of bacterial meningitis consist of fever, signs of increased intracranial pressure, and cerebral dysfunction. The fever in children who have bacterial meningitis usually is greater than 38.3 degrees C. Increased intracranial pressure initially is manifested as
vomiting and lethargy. Older children and adolescents frequently present
with headache, fever, altered sensorium, and meningismus. Kernig's or
Brudzinski's signs may be absent in 50% of adolescents and adults with
bacterial meningitis. How do you diagnose meningitis? Meningitis is frequently associated with acute otitis media, pneumonia, and even gastroenteritis. The most important consideration in suspecting acute bacterial meningitis in the child or infant is his interaction with the environment. The child who is difficult to console, paradoxically irritable (increasingly agitated with parental comforting), or appears toxic should be suspect. Lumbar puncture is recommended in the young child or infant who fails to follow your examination or who interacts inappropriately. All febrile neonates less than 2 months of age should undergo a full septic work-up, with initiation of empiric antibiotic treatment. This evaluation includes bacterial cultures of urine, blood, and CSF. Children between 2 and 24 months old. In these younger children, the initial presentation of early meningitis is often non-focal, with fever, lethargy, irritability, and/or vomiting. Only 48% of infants with bacterial meningitis will have positive meningeal signs, including nuchal rigidity or Kernig's or Brudzinski's signs. A high index of suspicion for meningitis is essential when evaluating the febrile infant 12 months of age or younger. Lumbar Puncture Analysis of CSF by LP is the basis for evaluation of suspected meningitis. A CT scan is not necessary prior to an LP In children without evidence of increased intracranial pressure, focal neurological findings, or papilledema. If increased intracranial pressure is suspected, LP should be postponed, a blood culture obtained and empiric antimicrobial therapy initiated while the CT scan is pending. CSF studies include cell count, protein, glucose, bacterial culture, and Gram's stain. Opening pressures are helpful in older children and adults, but they are usually not obtained in the infant age group. Prior administration of antibiotics has minimal effect on CSF findings in bacterial meningitis. CSF glucose of less than 40 mg/dL or a CSF glucose-to-blood glucose ratio of less than 0.3-0.5 suggests bacterial meningeal infection, as does a CSF protein of more than 150-170 mg/dL in neonates, or 40-50 mg/dL in older infants and children. In HIV-positive children, India ink, cryptococcal antigen, acid fast bacillus (AFB) smear and culture, and fungal cultures are obtained. Children with a history of tuberculosis exposure or travel to an area endemic for tuberculosis should have a CSF AFB smear and culture. Higher WBC counts (>1000 cell/mm3) with a predominance of polymorphic neutrophils (PMNs) are associated with bacterial meningitis; however, a finding of fewer WBCs (or <50% PMNs) may be seen with early bacterial disease. A small number of patients with bacterial meningitis may present with normal CSF indices. Therefore, a child who clinically appears ill, even with a normal spinal fluid analysis, mandates immediate empiric antimicrobial therapy and hospital admission. Repeat LP 12-24 hours later may reveal a conversion to CSF indices consistent with bacterial infection.
Associated Diagnostic Work-up Complete blood count (CBC) should be obtained, but a normal WBC count does not exclude a significant bacterial infection. Serum electrolytes and glucose are obtained as a baseline and to exclude the syndrome of inappropriate antidiuretic hormone (SlADH). Bacterial antigen tests of CSF (latex agglutination and counter immunoelectrophoresis) are usually of little value. However, children on antibiotics for another focus of infection who present with partially treated meningitis, may have falsely negative cultures, and latex agglutination or other rapid antigen detection test may yield a diagnosis. False-positive and false-negative results are common. Blood cultures are obtained to rule out sepsis or bacteremia and to increase the diagnostic yield for a bacterial pathogen. Treatment of Meningitis Antibiotics Antibiotics should be initiated immediately on suspicion of bacterial meningitis. Initial agents are chosen empirically because culture results will not be available for 24 hours. In neonates without grossly purulent CSF, ampicillin and gentamicin are the agents of choice while awaiting culture results. Three weeks of parenteral therapy is required.
Supportive Care Maintenance of normal blood glucose, appropriate blood volume, blood pressure and oxygenation, and management of increased intracranial pressure have a greater impact on outcome than the specific antibiotic chosen. Restricting fluids to two-thirds maintenance, after the intravascular volume has been replaced, is recommended to prevent cerebral edema. Dexamethasone Administration of dexamethasone during the treatment of H influenzae meningitis reduces the incidence of subsequent sensorineural hearing loss. Dexamethasone is administered to children older than 3 months of age with bacterial meningitis. The dosage is 0.15 mg/kg IV q6h for the first 4 days. The effect is maximized if it is administered 10 minutes before the first dose of antibiotics. Acute Complications of Bacterial Meningitis Cerebral Edema Within the first 2 days of bacterial meningitis, the most common complication is cerebral edema. Restricting fluids to two-thirds maintenance after intravascular volume has been restored will minimize the likelihood of cerebral edema. Increased intracranial pressure, secondary to cerebral edema manifests as coma, absence of a oculocephalic reflex (ie, fixed response to the doll head maneuver), or fixed eye deviation. Increased intracranial pressure is managed with mannitol and surgical decompression. Acute intervention is warranted to avoid cerebral or cerebellar herniation. Subdural Empyema Subdural empyema usually occurs in infants with severe Gram-negative meningitis. Coma and increased intracranial pressure with intermittent decorticate posturing may be followed by seizures. Cranial computed tomography with contrast will reveal a subdural collection of fluid. Ventriculitis Ventriculitis is a common complication of Gram-negative and group B streptococcal meningitis in neonates. This disorder is manifest by clinical worsening in a neonate being treated with appropriate antibiotics whose CSF sampled from the lumbar area shows improvement. Apneic spells and bradycardia often occur. Cranial CT may identify fluid of different contrast densities in the ventricles. The diagnosis is confirmed by ventricular puncture. Brain Abscess is an uncommon complication of bacterial meningitis; it most commonly occurs as a complication of H influenzae disease and is manifested by a focal motor deficit. Chemoprophylaxis for Pediatric Meningitis Haemophilus Influenzae (HiB) Household contacts should receive rifampin only if there is one or more child less than 4 years of age living in the household. All members of the household, including those previously immunized, and the patient should receive prophylaxis with rifampin. Daycare contacts may receive prophylaxis if two or more cases of invasive HiB disease occur within two months. In smaller daycare settings with children <2 years, prophylaxis after a single case may be recommended. Rifampin Prophylaxis: 20 mg/kg single daily dose (maximum, 600 mg/d) PO for four days. Neisseria Meningitidis All household and daycare contacts, and anyone with close contact with oral secretions should receive prophylaxis. Rifampin Prophylaxis: 20 mg/kg/d (maximum, 600 mg/d) q12h PO for two days. Streptococcus Pneumoniae. Chemoprophylaxis is not indicated. §
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