Enteroviruses and parechoviruses cause meningitis with peaks during summer and fall in temperate climates. These infections are more prevalent among low socioeconomic groups, young children, and immunocompromised persons. The prevalence of arboviral meningitis is determined by geographic distribution and seasonal activity of the arthropod (mosquito) vectors. In the United States, most arboviral infections occur during the summer and fall.
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Preceding upper respiratory tract symptoms are common. Rapid onset is typical of S. pneumoniae and N. meningitidis.Indications of meningeal inflammation include headache, irritability, nausea, nuchal rigidity, lethargy, photophobia, and vomiting. Fever usually is present. Kernig and Brudzinski types a, b, c, d, e, f, and nontypable
Table 100-2 Cerebrospinal Fluid (CSF) Findings in Various Central Nervous System Disorders CONDITION PRESSURE LEUKOCYTES (/µL) PROTEIN (mg/dL) GLUCOSE (mg/dL) COMMENTS Normal 50–180 mm H2O <4; 60%–70% lymphocytes, 30%–40% monocytes, 1%–3% neutrophils 20–45 >50% of serum glucose
HSV, Herpes simplex virus; IGRA, interferon gamma release assay for tuberculosis; PCR, polymerase chain reaction; PMNs, polymorphonuclear leukocytes; TST, tuberculin skin test.
signs of meningeal irritation are often positive in children older than 12 months. In young infants, signs of meningeal inflammation may be minimal with only irritability, restlessness, depressed mental status, and poor feeding present. Focal neurologic signs, seizures, arthralgia, myalgia, petechial or purpuric lesions, sepsis, shock, and coma may occur. Symptoms of increased intracranial pressure include headache, diplopia, and vomiting; a bulging fontanelle may be present in infants. Ptosis, sixth nerve palsy, anisocoria, bradycardia with hypertension, and apnea are signs of increased intracranial pressure with brain herniation. Papilledema is uncommon, unless there is occlusion of the venous sinuses, subdural empyema, or brain abscess.
If bacterial meningitis is suspected, a lumbar puncture shouldbe performed unless there is evidence of cardiovascular instability or of increased intracranial pressure (because of the risk ofherniation), other than a bulging fontanelle. Routine CSF examination includes a white blood cell count, differential, proteinand glucose levels, and Gram stain (Table 100-2). CSF should be cultured for bacteria and, when appropriate, fungi, viruses, andmycobacteria. The polymerase chain reaction is used to diagnose enteroviruses, parechoviruses, and herpes simplex virus;it is more sensitive and rapid than viral culture. Peripheral leukocytosis is common, and blood cultures are positive in 90%of cases of bacterial meningitis. An electroencephalogram mayconfirm an encephalitis component (see Chapter 101).
Many disorders may show signs of meningeal irritation and increased intracranial pressure, including the infectious causes of meningitis or encephalitis, hemorrhage, rheumatic diseases, and malignancies. Seizures are associated with meningitis, encephalitis, and intracranial abscess or can be the sequelae of brain edema, cerebral infarction or hemorrhage, or vasculitis.