possibility of neurologic disease must be assessed simultaneously with the assessment of the
patient’s overall medical status.
A general examination should initially focus on vital signs—remembering that fever may
not be evident at either end of the age spectrum or in those with compromised immunity. The
examination must seek evidence of pulmonary, hepatic, or renal compromise. Finally, a limited
neurologic assessment, focusing on language, orientation, and cranial nerve function is
essential. Key biochemical markers, including glucose, sodium, liver and renal function and, if
relevant, blood gases, should similarly be assessed immediately. If none of this reveals
significant extra-neurologic disease, focus should shift to the nervous system.
If either the history or examination suggests a primary CNS process, brain imaging
(usually, in the interest of timeliness, with computerized tomography) is usually rapidly
completed. If this does not demonstrate significant focal mass effect, and the picture does not
clearly suggest a noninfectious cause, a lumbar puncture should be performed. Spinal fluid
studies should include cell count, differential, protein, glucose (with simultaneous blood
glucose!), bacterial culture, and Gram stain. Depending on the context, additional studies may
include mycobacterial cultures and PCR, fungal cultures, CSF RPR, paired serum and CSF
Lyme serologies, PCR for herpes viruses, serologic and PCR testing for West Nile virus, etc.
Blood cultures should normally be obtained as well if there is serious consideration of a
nervous system bacterial infection. Initial treatment is often started empirically, depending on
context, to cover likely pathogens.
CONCLUSIONS
Although alterations of nervous system function can arise from a broad range of disorders, a
logical clinical approach can lead to rapid diagnosis in most. Fortunately CNS infection is
statistically rare. However, when encephalitis does occur, its results can be devastating; generally
the earlier the treatment can be initiated the better the likelihood of a favorable outcome.
REFERENCES
- Whitley R, Kimberlin D, Roizman B. Herpes simplex viruses. Clin Infect Dis 1998; 26:541–553.
- Halperin J. Viral encephalitis. In: Halperin J, ed. Encephalitis—Diagnosis and Treatment. New York:
Informa; 2007:115–132.
Figure 1 Clinical approach to the patient with altered brain function.
162 Halperin