The differential diagnoses may be categorized into parenchymal or meningeal disorders. When fever and focal neurologic symptoms and signs predominate, parenchymal central nervous system infections are concerns (e.g., brain abscess, viral encephalitis, cerebral toxoplasmosis, and other parenchymal processes). When meningeal signs predominate, other infectious meningitides, meningeal neoplasm, and subarachnoid hemorrhage are possible.

For evaluation of parenchymal brain infections, LP is unhelpful and potentially dangerous, since it can lead to transtentorial or tonsillar herniation. A cranial computed tomography (CT) scan should be done first if the patient exhibits papilledema or focal neurologic signs. A cranial CT scan is also the preferred mode in diagnosing subarachnoid hemorrhage.

For meningeal disorders other than subarachnoid hemorrhage, CSF examination is most helpful. Typical CSF findings for bacterial, viral, neoplastic, and fungal meningitides are displayed in T§bJ.e...22.7..-.2, but there is considerable overlap in findings. Some bacteria (e.g., Mycoplasma, Listeria, spirochetes, syphilis, Leptospira, and Borrelia) produce CSF alterations that in T.a.bIe 2.2.7.-.2.. An aseptic profile, suggesting viral infection, is typical of partially treated bacterial infections (one-third or more of pediatric cases have received antimicrobial treatment before presenting with meningitis). The same is true of untreated bacterial infections adjacent to but not communicating with the subarachnoid space, such as abscesses of the brain and subdural or epidural spaces. The percentage of polymorphonuclear cells may be higher in early viral meningitis, and glucose levels may be reduced in some viral cases.

TABLE 227-2 Typical Spinal Fluid Results for Meningeal Processes

Additional helpful tests may include viral cultures in suspected viral meningitis, tests for Borrelia antibodies in patients with possible Lyme disease, india ink and latex agglutination assay for fungal antigen in cryptococcal meningitis (serum cryptococcal antigen, if available, obviates this CSF analysis), acid-fast stain and culture for mycobacteria in tuberculous meningitis, and latex agglutination or counterimmune electrophoresis for bacterial antigens in potentially partially treated bacterial cases. Assays are most widely available for S. pneumoniae, other group B streptococci, H. influenzae type b, and N. meningitidis. Rarely, CSF may be normal or nearly so in very early bacterial meningitis, especially during meningococcemia. Empiric antibiotic treatment, admission, and repeated LP are appropriate if clinical suspicion is great despite negative initial CSF results.8

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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