PHYSICAL EXAMINATION

VS: T 38.5°C, P 102/min, R 20/min, BP 118/60 mmHg

PE: On examination, the patient was difficult to arouse and did not respond appropriately to questioning. A coarse tremor was present in the chin and upper and lower extremities.

LABORATORY STUDIES

Blood

Hematocrit: 37%

WBC: 11,600/μL

Differential: 72% PMNs, 8% lymphs, 15% monos

Blood gases: Normal

Serum chemistries: AST 58 U/L

Imaging

Head CT was unremarkable, and brain MRI showed increased signal in the basal ganglia.

Table 89-1 lists the likely causes of illness (differential diagnosis). Diagnosis of encephalitis on clinical grounds alone is difficult. There are not enough specific findings on physical examination. A high index of suspicion in the summer months in the appropriate geographic areas may support a presumptive diagnosis of arboviral encephalitis. Lumbar puncture is performed, and CSF is examined to rule out bacterial and viral meningitis. The CSF of patients with arboviral encephalitis may reveal lymphocytic leukocytosis, with a normal protein and a normal glucose level. Further investigational approach may include

• Cultivation of neurotropic virus in CSF

• Direct cryptococcal antigen in CSF

• Viral serology

• Presence of specific IgM in acute-phase serum or CSF

• Elevated arboviral IgG between early and late specimens of serum

• PCR amplification of DNA from CSF to rule out a neurotropic virus (e.g., HSV-1)

TABLE 89-1 Differential Diagnosis and Rationale for Inclusion (consideration)

Arthropod-borne encephalitides

California/LaCrosse virus

Eastern equine virus

St. Louis virus

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