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Tuesday, January 06, 2009
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How
Lyme Disease Is Diagnosed
Lyme disease may be difficult to diagnose because many of its
symptoms mimic those of other disorders. In addition, the only
distinctive hallmark unique to Lyme disease-the erythema migrans
rash-is absent in at least one-fourth of the people who become
infected. The results of recent studies indicate that an infected
tick must be attached to a person's skin for at least 2 days to
transmit the Lyme bacteria. Although a tick bite is an important
clue for diagnosis, many patients cannot recall having been bitten
recently by a tick. This is not surprising because the tick is
tiny, and a tick bite is usually painless.
When a patient with possible Lyme disease symptoms does not develop
the distinctive rash, a physician will rely on a detailed medical
history and a careful physical examination for essential clues
to diagnosis, with laboratory tests playing a supportive role.
Early Infection
- EM Rash
(erythema migrans)
- Muscle and
joint aches
- Headache
- Fever
- Fatigue
Early Disseminated
Infection
- Multiple
EM lesions
- Facial paralysis
(Bell's palsy)
- Meningitis
- Radiculitis
(numbness, tingling, burning)
- Brief episodes
of joint pain and swelling
Late Infection
- Arthritis,
intermittent or chronic
- Encephalopathy
(mild to moderate confusion)
Less Common
Symptoms of Lyme Disease
- Heart abnormalities
- Eye problems
such as conjunctivitis
- Chronic
skin disorders
- Encephalomyelitis
(limb weakness, motor coordination)
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Blood Tests. Unfortunately, the Lyme disease
microbe itself is difficult to isolate or culture from body tissues
or fluids. Most physicians look for evidence of antibodies against
B. burgdorferi in the blood to confirm the bacterium's
role as the cause of a patient's symptoms. Antibodies are molecules
or small substances tailor-made by the immune system to lock onto
and destroy specific microbial invaders.
Some patients experiencing nervous system symptoms may also undergo
a spinal tap. Using this procedure, doctors can detect brain and
spinal cord inflammation and can look for antibodies or genetic
material of B. burgdorferi in the spinal fluid.
The inadequacies of the currently available diagnostic tests may
prevent physicians from firmly establishing whether the Lyme disease
bacterium is causing a patient's symptoms. In the first few weeks
following infection, antibody tests are not reliable because a
patient's immune system has not produced enough antibodies to
be detected. Antibiotics given to a patient early during infection
may also prevent antibodies from reaching detectable levels, even
though the Lyme disease bacterium is the cause of the patient's
symptoms.
The antibody test used most often is called an ELISA test. When
an ELISA is positive, it should be confirmed with a second, more
specific test, called a Western blot.
![[Borrelia burgdorferi]](bbmicro.jpg) Physicians must rely on their clinical judgment in diagnosing
someone with Lyme disease even though the patient does not have the distinctive
erythema migrans rash. Such a diagnosis would be based on the time of
year, history of a tick bite, the patient's symptoms, and a thorough ruling
out of other diseases that might cause those symptoms. Doctors may consider
such factors as an initial appearance of symptoms during the summer months
when tick bites are most likely to occur, and outdoor exposure in an area
where Lyme disease is common.
New Tests Under Development. To improve the accuracy
of Lyme disease diagnosis, NIH-supported researchers are developing
a number of new tests that promise to be more reliable than currently
available procedures.
NIH scientists are developing tests that use the highly sensitive
genetic engineering technique, known as polymerase chain reaction
(PCR), to detect extremely small quantities of the genetic material
of the Lyme disease bacterium in body tissues and fluids.
A bacterial protein, outer surface protein (Osp) C, is proving
useful for the early detection of specific antibodies in people
with Lyme disease.
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Last Updated February 25, 1999 (kap)
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