Delaware County Medicine & Health Winter 2017 - 21

It usually takes at least 36 hours of tick attachment
for spirochete to be injected into the human skin.
Infection can occur with attachments of shorter
duration if the tick fed previously. Other tickborne infections, such as the Powassan virus, can be
transmitted within minutes of initial tick attachment.
After entering the skin, the Lyme spirochete travels via
the bloodstream to various tissues including the brain, joints,
heart, peripheral nerves, muscles, and connective tissue. In
about 70% of cases, an expanding skin rash develops in the
weeks following the infection. It often appears as a reddish
or purple oval, but as it spreads, it may look like a target with
a red perimeter and a central clearing. It is important to note
that some patients never develop or not notice this rash.
Other symptoms of Lyme disease may develop quickly or
they may take up to months or even years to develop as the
spirochetes are adept at evading the human immune response.
Since symptoms and signs of Lyme disease can be diverse
and blood tests are not 100% reliable, diagnosis is often based
on the patient's clinical history, which is then supplemented
by blood test results. It is important for the clinician to ask
for a full medical history, including any tick bites or rashes.
These criteria are not very helpful, however, for
assisting the clinician in detecting Lyme disease when
these markers are not present. For example, in early
Lyme disease, about 30% of patients do not recall
the rash. These patients might instead present with
marked fatigue, muscle pains and headaches, and be
incorrectly diagnosed as having a viral illness.

In the early 1990s, the Centers for Disease Control
and Prevention (CDC) delineated a set of criteria for the
diagnosis of Lyme disease to be used by public health
officials	to	count	the	number	of 	new	Lyme	disease	cases	each	
year. Although it was recognized that the manifestations of
Lyme disease are quite diverse and not entirely represented
by the CDC "surveillance criteria," these criteria were
narrowly	defined	on	purpose	to	ensure	with	a	high	degree	
of certainty that all patients included had proven Lyme
disease. These criteria rely on the externally visible signs, such
as the typical erythema migrans rash, arthritis, facial nerve
palsy,	or	meningitis	with	abnormal	spinal	fluid	markers.	

In late stage neurologic Lyme disease, one of the
more common manifestations is a mild to moderate
encephalopathy,	with	non-specific	symptoms	of 	memory	
problems and fatigue, but the physician may not consider
Lyme disease in the differential diagnosis because he or
she mistakenly relies too heavily on the CDC surveillance
criteria. Even if this patient is shown to have a positive
blood test for Lyme disease, the physician may mistakenly
dismiss	it	as	insignificant	because	the	clinical	manifestations	
fall	outside	of 	the	CDC's	surveillance	definition.	The	
CDC recognizes that there are clinical manifestations of
Lyme disease that fall outside of the narrow criteria used
for	the	case	definition.	This	should	not	be	considered	
as an error by the CDC but rather as an error by
physicians who misapply the CDC surveillance criteria,
inappropriately using these narrow criteria developed for
epidemiologic surveillance to exclude clinical cases that
do	not	meet	the	strict	"surveillance	case	definition."			

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Table of Contents for the Digital Edition of Delaware County Medicine & Health Winter 2017
