Diagnosis? What’s Your I Mosquitoes on the Attack?

What’s Your
Diagnosis?
Mosquitoes on the Attack?
By Irving Salit, MD, FRCPC
n early September, while in central Ontario, Peter, 61,
noted fever, urinary frequency, dysuria, abdominal pain,
back pain, and achiness in his legs. He was started on
ciprofloxacin and phenazopyridine, but he did not improve. His
urine culture was negative. He felt he had some leg weakness and had difficulty walking. Peter’s travel history included a trip to Italy in July and a
stay at a cottage around Georgian Bay, Ontario in August.
Because of the fever and back pain, he was admitted to hospital
with a diagnosis of possible pyelonephritis or prostatitis.
Investigations in hospital
did not reveal any uriTable 1
nary tract obstruction, although there was a cyst in his
Examination and laboratory
test results
right kidney. In hospital, he had chills and rigors, with a
Physical examination
temperature of 38.5 C. He was switched from
• No definite flank tenderness
ciprofloxacin to ampicillin and gentamicin.
During hospitalization, he started to develop a slight
• Tremor of the left hand
left-sided tremor. Magnetic resonance imaging did not
• Mild confusion
reveal any new lesions to account for the tremor. He was previ• Neurologic exam: Otherwise normal
ously noted to have an acoustic neuroma which was unchanged.
Lab tests
Results of the physical and laboratory examinations are shown in
• Hemoglobin: 135 g/L
Table 1.
• White blood cells: 11.2
When seen in a followup one month after the onset of his orig• Creatinine: Normal
inal symptoms, he still had a tremor and difficulty with fine
• Transaminases: Normal
motor skills. The tremor interfered with his ability to write and he
• Albumin: Normal
found it most noticeable when had to sign his name; his signature
• Urinalysis/Urine culture: Negative
was no longer recognizable as being his own. An additional test
was done which revealed the cause of his problem.
I
What’s your diagnosis?
Dr. Salit is an associate professor, University of Toronto,
and a staff member, division of infectious diseases,
University Health Network, Toronto General Hospital,
Toronto, Ontario.
See page 40 for the answer
The Canadian Journal of Diagnosis / August 2003
37
What’s Your Diagnosis ?
Answer: West Nile virus
This patient’s predominant symptoms included an initial febrile illness followed
by a tremor. There was some unsteadiness of gait and subtle confusion.
Because of the large number of cases of West Nile virus infection occurring in
Ontario, the patient’s blood was sent for arbovirus serology. Antibody titres to
both St. Louis encephalitis and West Nile virus were 1:≥ 640 at one month and
four months after the onset of his illness. Cross-reactions can occur among
arboviruses, such as St. Louis encephalitis, Dengue fever, West Nile virus,
Powassan encephalitis, Yellow fever, and Japanese encephalitis, but West Nile was
geographically most likely.
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More on West Nile virus
In 2002, there was a 65-fold increase in the number of West Nile virus cases in the
U.S. Similarly, during 2002, West Nile virus activity was detected in birds and mosquitoes in many areas of southern Ontario. During August and September 2002,
there were many patients admitted to hospital with neurologic disorders which
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Table 2
turned out to be West Nile
encephalitis. Patients admitted
to hospital with West Nile virus
had the most severe forms of
the disease. The main symptoms of those hospitalized for
West Nile virus and the prevalence of those symptoms are
listed in Table 2.
The neurologic dysfunction
with West Nile virus usually
starts several days after the
onset of systemic symptoms,
such as fevers and myalgias.
Most patients with severe West
Nile virus neurologic disease
are over age 50 and about half
have significant underlying disease. The mortality rate is
almost 20% and survivors very
frequently have chronic and
persistent neurologic deficits.
Neurologic manifestations of West
Nile and their prevalence
Symptom
Prevalence
• Decreased level of
consciousness
75%
• Neuromuscular
weakness
40%
• Dysphagia
34%
• Ataxia
30%
• Dysarthria
17%
• Vertigo
14%
• Intention tremor
13%
Some of the most severe neuromuscular
manifestations include coma and flaccid
quadriparesis.
What happened
to Peter?
The patient presented here had a
milder form of West Nile virus
encephalitis, which did improve
over the ensuing months. In fact,
after six months he was
essentially normal. Without a
high index of suspicion, many
other cases of milder forms of
West Nile virus encephalitis
have probably occurred and have
not been recognized. Dx
3