Lyme Disease and Related Tick-Borne Infections
DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of Lyme Disease.
Alternative NamesBabesiosis; Human Granulocytic Ehrlichiosis
Proper diagnosis of Lyme disease is important. A diagnosis of Lyme disease is straightforward if the patient meets the following criteria:
If the patient has all of these symptoms, except the rash, then the physician may undertake the enzyme-linked immunosorbent assay (ELISA) or the Western Blot test.
In some cases, if the patient seeks a diagnosis within the first two or three weeks, the physician may take a sample of the skin or of the blood. If Lyme spirochete is present, it may be identified in the laboratory in a culture medium (a substance in which the organism can thrive and reproduce). This is necessary only if a physician suspects Lyme but the diagnosis is not clear. Basically, it is a research technique.
If the infection is not obvious from the patient's history and physical symptoms but Lyme disease is suspected, the physician may run tests for evidence of specific factors that suggest infection with B. burgdorferi. Such factors include the following:
Tests have now been developed to detect either the antibodies that attack the Osps or the Osps themselves.
Research is underway to create more accurate immune system tests for Lyme disease. One blood test, for example, can directly identify the Osp A protein itself (not just the antibodies to it), which would provide direct evidence of the Lyme spirochete. However, widespread use of this test is probably years away.
Accuracy of the Tests. It should be noted that these tests are very expensive and none are completely accurate in either identifying Lyme or ruling it out. They should never be used to make a primary diagnosis of Lyme disease in patients who do not have obvious symptoms of the disease.
Either false positive and false negative results are common with these tests.
False positive results occur when the test suggests the presence of the disease, but the person does not actually have an active infection. This may occur in different ways:
False negative results are those that miss the actual presence of the disease. These results are also common. (If the results are negative but Lyme disease is highly suspected, the physician will probably prescribe antibiotics anyway.) False negative results occur for a number of reasons:
In summary, a negative blood test does not rule out a diagnosis of Lyme disease, particularly if symptoms strongly suggest its presence. Conversely, a weakly positive blood test does not prove that Lyme disease is causing the symptoms. A second blood test, taken several weeks later, may help.
Polymerase Chain Reaction (PCR) Test
The polymerase chain reaction (PCR) test is a sophisticated approach that makes multiple copies of a specific region of unknown but suspicious DNA found in urine or blood. Once it produces enough DNA, it can be tested to see if matches the DNA of B. burgdorferi. The test allows detection much more quickly than a culture. This test may be particularly useful in detecting Lyme disease in people who still have persistent symptoms after being treated with antibiotics. It has limitations, however. For one, it requires strict controls to be accurate, and at this time can be performed only in a few laboratories in the country. It can also fail to identify the Lyme spirochete, since organisms do not always show up in bodily fluids at the time the test is being taken. At this point, it is reserved for certain patients with specific diagnostic problems.
Tests for Neurologic Involvement
Analysis of Spinal Fluid. In patients who have neurologic symptoms, a lumbar puncture (a spinal tap) may be used to test for the bacteria in spinal fluid and may be useful for an early diagnosis of Lyme disease. PCR testing is more accurate than attempts to culture the spirochete in the fluid.
Imaging Tests. An advanced imaging test called single photon emission computed tomography (SPECT) is showing promise for revealing patterns in the brain that are indicative of central nervous system involvement in Lyme disease. Other imaging tests, including computed tomography (CT) scans and magnetic resonance imaging (MRI) tests, are not useful.