Meningitis PDF

Meningitis Disease Summary ○ Definition: Acute pyogenic meningitis (APM) is a potentially fatal inflammation of the leptomeninges of the brain and spinal cord (i.e., pia mater and arachnoid), the cerebrospinal fluid (CSF)-filled subarachnoid space, and ventric...

Meningitis Disease Summary ○ Definition: Acute pyogenic meningitis (APM) is a potentially fatal inflammation of the leptomeninges of the brain and spinal cord (i.e., pia mater and arachnoid), the cerebrospinal fluid (CSF)-filled subarachnoid space, and ventricular system. ○ Although many types of microbes cause meningitis, APM is most often caused by a variety of bacteria. ○ As a result, APM is also known as bacterial meningitis. ○ Since CSF circulates around and through the brain and spinal cord, APM is typically an extremely rapidly spreading infection. Prevalence ○ Older adults also tend to have a higher incidence of meningitis than do young children. ○ The median age of patients is currently 25 years. ○ The incidence of neonatal APM is 0.25–1 case per 1,000 live births and 2.5 cases per 1,000 premature births. ○ Among neonates, male-to-female ratio is 3:1. ○ Although race may not be an independent risk factor, incidence rates for APM are higher in pediatric African-American and Native American populations. Causes and risk factors ○ There are numerous bacterial causes of APM and the cause is often related to the patient’s age. ○ Risk factors are related to infections that spread to the meninges by extension or through the bloodstream, to significantly reduced immune defenses in the patient, or to a combination of these conditions ○ Risk factors include: respiratory tract infection otitis media (i.e., middle ear infection) mastoiditis (i.e., inflammation of any part of the mastoid process of the temporal bone) Sinusitis Neurosurgery head trauma Alcoholism use of high-dose corticosteroids Splenectomy sickle cell disease immunoglobulin deficiency Pathophysiology infections: ○ That cause APM typically originate in another part of the body. ○ Microbes pass through the bloodstream and localize in the meninges (e.g., as with pneumococcal pneumonia) or directly extend from an infected area to the subarachnoid space (e.g., as with a sinus infection). ○ Central nervous system (CNS) bacterial pathogens are often surrounded by polysaccharide capsules that protect microbes from eradication by white blood cell phagocytosis. ○ 1 month to 29 years of age Haemophilus influenzae, Neisseria meningitidis (meningococcus), and Streptococcus pneumoniae (pneumococcus) ○ 30–60 years of age S. pneumoniae and N. meningitidis ○ 60 years of age S. pneumoniae, gram-negative enterics, and L. monocytogenes ○ Exudate accumulates rapidly, increases the viscosity of CSF, interferes with normal CSF flow around the brain and spinal cord, and causes an increase in both intraventricular and intracranial pressure. ○ Shows a case of APM in which the meninges have been stripped away and a thick, cream-colored exudate fills the subarachnoid space ○ Polymerase chain reaction testing of CSF for detecting bacteria provides results within hours. ○ A CT (i.e., computed tomography) scan is performed prior to lumbar puncture if a brain abscess is suspected (i.e., the patient also presents with papilledema, coma, seizure, or focal neurologic findings). ○ A spinal tap in the presence of a brain abscess may cause herniation of the brainstem, which may be immediately life-threatening. ○ Patients with APM usually seek medical assistance within 48 hours after the onset of symptoms. ○ As described above, the microbial agent responsible is often closely linked to the age of the patient. ○ Certain clinical manifestations are common to all types of CNS infections in adults and include the following: Headache fever with chills sensorial disturbances neck and back stiffness nausea and vomiting photophobia (i.e., an extreme sensitivity of the eyes to light) CSF abnormalities positive Kernig sign (i.e., patient in the supine position with the hips at 90° flexion senses pain in the hamstrings upon extension of the knees) positive Brudzinski sign (i.e., patient in the supine position flexes the knees in response to flexion of the neck) Positive Kernig and Brudzinski signs are caused by stretching of the inflamed meninges, which is very painful. Although it is rare for all of the clinical manifestations listed above to be present, the presence of even one should suggest the possibility of a CNS infection. Young infants with APM may have more non-specific clinical manifestations, such as irritability, an altered sleeping pattern, a high-pitched cry, and decreased appetite. ln older children, a more CNS-specific clinical picture becomes more prevalent.  A decrease in activity level, somnolence, confusion, and lethargy are frequently reported ○ Diagnosis is often established based on tests performed on the CSF (i.e., a Gram-stained smear, which is positive in up to 80% of patients with APM) and culture (which is positive in 90% of cases). ○ Other typical CSF findings include: CSF is cloudy in appearance neutrophil count of 200–200,000/mm3 glucose concentration 50% of the patient’s serum glucose level (because bacteria in the CSF utilize glucose to maintain their metabolic needs) elevated protein concentration (50 mg/dL) When the pathogen is identified, antibiotic therapy should be tailored toward the specific microbe: ○ For S. pneumoniae and N. meningitidis, the antibiotic of first choice is penicillin G; ○ For H. influenzae, the antibiotics of first choice are cefotaxime (if the microbial strain is β-lactamase producing) and ampicillin (if non–β-lactamase producing); ○ For Escherichia coli, the antibiotics of first choice are cefotaxime or ceftriaxone;