Lyme disease: Staying on track
Lyme disease is the most common vector-borne illness in the United States. The spirochete, which causes the disease, is transmitted by Ixodes ticks, which have geographic distributions. For a person to develop Lyme disease, he or she must be bitten by an infected tick. The organism is transmitted only if the tick is infected and if the tick feeds long enough (ie, more than 36 hours).
New ticks hatch in the spring and the tick takes only one blood meal per stage. Newly hatched ticks are not yet infected, so they can’t transmit disease during the first blood meal. There are only three stages, and the adult ticks prefer deer. Thus, the major transmitters are the nymphs, which feed over the summer.
The hallmark of early localized Lyme disease is the bull’s eye rash: erythema migrans. The rash begins at the tick bite site and expands over days to reach diameters in excess of 5 cm. Generally, the border of the rash is erythematous, with central clearing, although at times the center is erythematous or even purplish. Fever, malaise, aches and pains often accompany the rash. The rash resolves with or without antibiotic therapy.
Some patients will develop early disseminated disease in which there are multiple erythema migrans. Cranial nerve palsies, most often the seventh nerve, may occur in this stage. Aseptic meningitis occurs in some patients and can be difficult to distinguish from viral meningitis. However, the onset is generally more insidious than viral meningitis. Carditis occurs in this stage but is rare in children; carditis presents as heart block.
Late disease is characterized by arthritis, generally pauciarticular, and most often involving the knees. Central nervous system disease and peripheral neuropathy are rare manifestations of late Lyme disease.
Importance of patient history
As with almost all illnesses, the diagnosis of Lyme disease should be based on the history and the clinical findings. The patient must have resided or traveled to an area where Ixodes ticks are present, and they must have spent time in an activity that would allow them to be bitten by a tick. The clinical findings should suggest and be consistent with Lyme disease.
Although serology is often relied upon to make the diagnosis, in my experience, it is often misleading. It takes weeks to develop an antibody response that can be detected by the usual serologic studies. Therefore, in early Lyme disease, serology is insensitive and should not be obtained. During late disease, serology should be positive; immunoglobulin G antibody should be present and IgM may be present.
The usual method for serology is a two-step process. A quantitative screen test for serum antibodies is performed by either enzyme immunoassay or immunofluorescent antibody assay. If this test is positive or equivocal, then Western immunoblot should be performed. If testing is performed in a patient with suspected early disseminated disease, both IgG and IgM immunoblots should be performed; if late Lyme disease is suspected, only IgG testing is necessary. The Western blot testing should not be performed if the screening test is negative. Further, the IgM test is often falsely positive.
Antibody persists for a variable amount of time. However, it is not protective and levels do not correlate with disease activity. There is no reason to obtain follow-up or serial titers. Currently, there is no serologic test of cure.
Lyme disease treatment
Treatment depends upon the stage of the infection. For children aged 8 years and older, doxycycline is given for 2 to 3 weeks; amoxicillin is used in younger children or those who cannot tolerate doxycycline. Parenteral therapy is reserved for patients with persistent arthritis or meningitis; however, many experts would consider repeating an oral course of antibiotics for arthritis and using doxycycline for meningitis. As with many infections, symptoms often persist after completion of an effective antibiotic course. There is no evidence that prolonged antibiotic courses are needed or are helpful.
Prevention of Lyme disease
Prevention relies on avoidance of tick bites or prompt removal of the tick before transmission of the spirochete occurs. Ticks are most common in high grass or weeds. In general, if you can see your shoes, you are not likely to be bitten. This was shown in a study of golfers that correlated likelihood of Lyme disease with time spent in the rough. Tick checks are important so that the tick can be removed promptly.
Finally, here are 10 suggestions to keep physicians on track: 1) Lyme disease occurs in areas where Ixodes live, and early Lyme disease is a clinical diagnosis; serology is not helpful; 2) Lyme serology is often falsely positive, so do not order it in patients with nonspecific complaints; 3) if you order a test simply because the parent “demanded or requested” it, you are the one who will have to deal with the results; 4) repeated testing is not helpful; 5) symptoms often persist after antibiotic therapy is completed and more antibiotic is not necessary, whereas tincture of time is usually curative; 6) if the patient’s symptoms are not due to Lyme disease, it should not be surprising that antibiotics will not make the patient feel better; 7) if someone comes to you with Lyme titers drawn during the winter and the IgG is negative, the patient does not have Lyme disease but certainly may have false-positive IgM bands and a falsely positive screening test; 8) there are several laboratories that perform a variety of tests that are not approved by the FDA and are often not standardized nor useful in the care of patients. Some of your patients will spend hundreds of dollars on unreliable tests; this is not a reason for you to prescribe antibiotics for “concern about Lyme disease” or abnormal test results in a person with nonspecific complaints; 9) Beware of physicians whose sole practice involves Lyme disease; and 10) there is no “Limes Disease!”
Disclosure: Fisher reports no relevant financial disclosures.