PHYSICAL EXAMINATION

VS: T 40°C, P 108/min, R 18/min, BP 138/78 mmHg

PE: The patient was not able to answer more than simple questions, and he frequently seemed to drift into sleep. The neck was supple, but neurologic exam was difficult due to poor cooperation. Slight tremors of the face and extremities were noted.

LABORATORY STUDIES

Blood

Hematocrit: 42%

WBC: 14,400/μL

Differential: Normal

Platelets: 210,000/μL

Serum chemistries: Sodium 128 mmol/L (other markers were normal)

Imaging

Chest x-ray was normal; head CT scan was normal (there was no evidence of hydrocephalus).

Table 60-1 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

• Cultures 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, rabies)

TABLE 60-1 Differential Diagnosis and Rationale for Inclusion (consideration)

Arthropod-borne encephalitides