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Appropriate laboratory testing in Lyme disease

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Release date: November 1, 2019
Expiration date: October 31, 2020
Estimated time of completion: 1 hour

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ABSTRACT

Testing for Lyme disease is challenging and if done incorrectly can lead to unnecessary treatment. To interpret serologic test results, first assess the patient’s pretest probability of infection based on the probability of exposure and clinical findings. Two-tiered testing remains the gold standard in diagnosing Lyme disease, although new guidelines may be published soon.

KEY POINTS

  • Lyme disease, the most common tick-borne infection in North America, is a complex multisystem bacterial disease caused by Borrelia burgdorferi.
  • Lyme disease preferably affects the skin, joints, and nervous system and presents with typical and atypical features. Certain clinical features are diagnostic. Its diagnosis is mainly clinical and epidemiologic and, when doubtful, is supported by serologic testing.
  • Standard 2-tiered testing is the diagnostic testing method of choice—enzyme-linked immunoassay followed by Western blot. Interpretation of the bands depends on the duration of infection.
  • When interpreting the test results, be aware of false-positives and the reasons for them.


 

References

Lyme disease is a complex multisystem bacterial infection affecting the skin, joints, heart, and nervous system. The full spectrum of disease was first recognized and the disease was named in the 1970s during an outbreak of arthritis in children in the town of Lyme, Connecticut.1

This review describes the epidemiology and pathogenesis of Lyme disease, the advantages and disadvantages of current diagnostic methods, and diagnostic algorithms.

THE MOST COMMON TICK-BORNE INFECTION IN NORTH AMERICA

Lyme disease is the most common tick-borne infection in North America.2,3 In the United States, more than 30,000 cases are reported annually. In fact, in 2017, the number of cases was about 42,000, a 16% increase from the previous year, according to the US Centers for Disease Control and Prevention (CDC).

Ixodes scapularis is the vector of Lyme disease in the eastern United States.  Infected nymphs account for most cases. From Sigal LH. Myths and facts about Lyme disease. Cleve Clin J Med 1997; 64(4):203–209.

Figure 1. Ixodes scapularis is the vector of Lyme disease in the eastern United States.
Infected nymphs account for most cases.

The infection is caused by Borrelia burgdorferi, a particularly arthritogenic spirochete transmitted by Ixodes scapularis (the black-legged deer tick, (Figure 1) and Ixodes pacificus (the Western black-legged tick). Although the infection can occur at any time of the year, its peak incidence is in May to late September, coinciding with increased outdoor recreational activity in areas where ticks live.3,4 The typical tick habitat consists of deciduous woodland with sufficient humidity provided by a good layer of decaying vegetation. However, people can contract Lyme disease in their own backyard.3

Table 1. US states with the highest average incidence of Lyme disease, 2015–2017.

Most cases of Lyme disease are seen in the northeastern United States, mainly in suburban and rural areas.2,3 Other areas affected include the midwestern states of Minnesota, Wisconsin, and Michigan, as well as northern California.4 Fourteen states and the District of Columbia report a high average incidence (> 10 cases per 100,000 persons) (Table 1).2

FIRST COMES IgM, THEN IgG

The pathogenesis and the different stages of infection should inform laboratory testing in Lyme disease.

It is estimated that only 5% of infected ticks that bite people actually transmit their spirochetes to the human host.5 However, once infected, the patient’s innate immune system mounts a response that results in the classic erythema migrans rash at the bite site. A rash develops in only about 85% of patients who are infected and can appear at any time between 3 and 30 days, but most commonly after 7 days. Hence, a rash occurring within the first few hours of tick contact is not erythema migrans and does not indicate infection, but rather an early reaction to tick salivary antigens.5

Antibody levels remain below the detection limits of currently available serologic tests in the first 7 days after exposure. Immunoglobulin M (IgM) antibody titers peak between 8 and 14 days after tick contact, but IgM antibodies may never develop if the patient is started on early appropriate antimicrobial therapy.5

If the infection is not treated, the spirochete may disseminate through the blood from the bite site to different tissues.3 Both cell-mediated and antibody-mediated immunity swing into action to kill the spirochetes at this stage. The IgM antibody response occurs in 1 to 2 weeks, followed by a robust IgG response in 2 to 4 weeks.6

Because IgM can also cross-react with antigens other than those associated with B burgdorferi, the IgM test is less specific than the IgG test for Lyme disease.

Once a patient is exposed and mounts an antibody-mediated response to the spirochete, the antibody profile may persist for months to years, even after successful antibiotic treatment and cure of the disease.5

Despite the immune system’s robust series of defenses, untreated B burgdorferi infection can persist, as the organism has a bag of tricks to evade destruction. It can decrease its expression of specific immunogenic surface-exposed proteins, change its antigenic properties through recombination, and bind to the patient’s extracellular matrix proteins to facilitate further dissemination.3

Certain host-genetic factors also play a role in the pathogenesis of Lyme disease, such as the HLA-DR4 allele, which has been associated with antibiotic-refractory Lyme-related arthritis.3

LYME DISEASE EVOLVES THROUGH STAGES

Lyme disease evolves through stages broadly classified as early and late infection, with significant variability in its presentation.7

Early infection

Early disease is further subdivided into “localized” infection (stage 1), characterized by a single erythema migrans lesion and local lymphadenopathy, and “disseminated” infection (stage 2), associated with multiple erythema migrans lesions distant from the bite site, facial nerve palsy, radiculoneuritis, meningitis, carditis, or migratory arthritis or arthralgia.8

Highly specific physical findings include erythema migrans, cranial nerve palsy, high-grade or progressive conduction block, and recurrent migratory polyarthritis. Less specific symptoms and signs of Lyme disease include arthralgia, myalgia, neck stiffness, palpitations, and myocarditis.5

Erythema migrans lesions are evident in at least 85% of patients with early disease.9 If they are not apparent on physical examination, they may be located at hidden sites and may be atypical in appearance or transient.5

If treatment is not started in the initial stage of the disease, 60% of infected patients may develop disseminated infection.5 Progressive, untreated infection can manifest with Lyme arthritis and neuroborreliosis.7

Noncutaneous manifestations are less common now than in the past due to increased awareness of the disease and early initiation of treatment.10

Late infection

Manifestations of late (stage 3) infection include oligoarthritis (affecting any joint but often the knee) and neuroborreliosis. Clinical signs and symptoms of Lyme disease may take months to resolve even after appropriate antimicrobial therapy is completed. This should not be interpreted as ongoing, persistent infection, but as related to host immune-mediated activity.5

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