A 2-year-old girl is brought to the office by her mother for evaluation of
fever. You have been the girl's physician since birth. While in the office, the
girl stiffens and then has bilateral, symmetrical shaking of her upper and
lower extremities; she becomes mildly cyanotic. The episode lasts for
approximately 45 seconds, after which she becomes relaxed and appears
to fall asleep. Vital signs at this time are temperature 40.0°C (104.0°F),
pulse 120/min, and respirations 40/min. On physical examination she has a
generally pink complexion and flushed cheeks. She is limp and somnolent
and responds with a cry to noxious stimulus. Tympanic membranes are
inflamed bilaterally, nose has a scant, clear discharge, and throat is mildly
erythematous. Lungs are clear to auscultation except for transmitted
upper airway sounds. Heart has rapid rate with a grade 1/6 systolic
murmur at the left sternal border. Complete blood count, blood culture,
lumbar puncture, and catheterized urine specimen are obtained and sent
for stat analysis. Acetaminophen is administered by rectal suppository.
Thirty minutes later the patient awakens and is smiling. She is afebrile.
Additional history discloses that she was born at term, she had an
uneventful neonatal course, she has normal growth and development, and
vaccinations are up-to-date. She has never had an episode similar to this.
Initial laboratory results are shown: Blood WBC 10,400/mm3
Neutrophils, segmented 25%
Neutrophils, bands 5%
Lymphocytes 65%
Monocytes 5%
Cerebrospinal fluid 0 RBC/mm3
Urinalysis Normal
Other laboratory studies are pending.
Two weeks later the patient is brought to the office for a follow-up visit.
Her mother says that she is doing well and she has had no recurrence of
her symptoms. Examination of the ears shows resolution of the otitis
media. Which of the following is the most important diagnostic step at
this time?
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