Lyme disease is a tick-transmitted infection caused by the spirochete Borrelia burgdorferi. Early symptoms include an erythema migrans rash, which may be followed weeks to months later by neurologic, cardiac, or joint abnormalities. Diagnosis is primarily clinical in early-stage disease, but serologic testing can help diagnose cardiac, neurologic, and rheumatologic complications that occur later in the disease. Treatment is with antibiotics such as doxycycline or ceftriaxone.
Lyme disease was recognized in 1976 because of close clustering of cases in Lyme, Connecticut and is now the most commonly reported tick-borne illness in the US. It has been reported in 49 states, but > 90% of cases occur from Maine to Virginia and in Wisconsin, Minnesota, and Michigan. On the West Coast, most cases occur in northern California and Oregon. Lyme disease also occurs in Europe, across the former Soviet Union, and in China and Japan. Onset is usually in the summer and early fall. Most patients are children and young adults living in heavily wooded areas.
Lyme disease is transmitted primarily by 4 Ixodes sp worldwide: Ixodes scapularis (the deer tick) in the northeastern and north central US, I. pacificus in the western US, I. ricinus in Europe, and I. persulcatus in Asia. In the US, the white-footed mouse is the primary animal reservoir for Borrelia burgdorferi and the preferred host for nymphal and larval forms of the deer tick. Deer are hosts for adult ticks but do not carry Borrelia. Other mammals (eg, dogs) can be incidental hosts and can develop Lyme disease. In Europe, sheep are hosts for the adult tick.
B. burgdorferi enters the skin at the site of the tick bite. After 3 to 32 days, the organisms migrate locally in the skin around the bite, spread via the lymphatics to cause regional adenopathy or disseminate in blood to organs or other skin sites. Initially, an inflammatory reaction (erythema migrans) occurs before significant antibody response to infection (serologic conversion).
Symptoms and Signs
Lyme disease has 3 stages:
The early and late stages are usually separated by an asymptomatic interval.
Erythema migrans (EM), the hallmark and best clinical indicator of Lyme disease, is the first sign of the disease. It occurs in at least 75% of patients, beginning as a red macule or papule at the site of the tick bite, usually on the proximal portion of an extremity or the trunk (especially the thigh, buttock, or axilla), between 3 and 32 days after a tick bite. Because tick nymphs are so small, most patients do not realize that they have been bitten. The area expands, often with clearing between the center and periphery resembling a bull's eye, to a diameter ≤ 50 cm. Darkening erythema may develop in the center, which may be hot to the touch and indurated. Without therapy, EM typically fades within 3 to 4 wk.
Evanescent lesions may appear as EM resolves. Mucosal lesions do not occur. Apparent recurrences of EM lesions after treatment are caused by reinfection, rather than relapse, because the genotype identified in the new lesion differs from that of the original infecting organism.
Symptoms of early-disseminated disease begin days or weeks after the appearance of the primary lesion, when the bacteria spread through the body. Soon after onset, nearly half of untreated patients develop multiple, usually smaller annular secondary skin lesions without indurated centers. Cultures of biopsy samples of these secondary lesions have been positive, indicating dissemination of infection. Patients also develop a musculoskeletal, flu-like syndrome, consisting of malaise, fatigue, chills, fever, headache, stiff neck, myalgias, and arthralgias that may last for weeks. Because symptoms are often nonspecific, the diagnosis is frequently missed if EM is absent; a high index of suspicion is required. Frank arthritis is rare at this stage. Less common are backache, nausea and vomiting, sore throat, lymphadenopathy, and splenomegaly.
Symptoms are characteristically intermittent and changing, but malaise and fatigue may linger for weeks. Some patients develop symptoms of fibromyalgia. Resolved skin lesions may reappear faintly, sometimes before recurrent attacks of arthritis, in late-stage disease.
Neurologic abnormalities develop in about 15% of patients within weeks to months of EM (generally before arthritis occurs), commonly last for months, and usually resolve completely. Most common are lymphocytic meningitis (CSF pleocytosis of about 100 cells/μL) or meningoencephalitis, cranial neuritis (especially Bell palsy, which may be bilateral), and sensory or motor radiculoneuropathies, alone or in combination.
Myocardial abnormalities occur in about 8% of patients within weeks of EM. They include fluctuating degrees of atrioventricular block (1st-degree, Wenckebach, or 3rd-degree) and, rarely, myopericarditis with chest pain, reduced ejection fractions, and cardiomegaly.
In untreated Lyme disease, the late stage begins months to years after initial infection. Arthritis develops in about 60% of patients within several months, occasionally up to 2 yr, of disease onset (as defined by EM). Intermittent swelling and pain in a few large joints, especially the knees, typically recur for several years. Affected knees commonly are much more swollen than painful; they are often hot, but rarely red. Baker cysts may form and rupture. Malaise, fatigue, and low-grade fever may precede or accompany arthritis attacks. In about 10% of patients, knee involvement is chronic (unremittent for ≥ 6 mo). Other late findings (occurring years after onset) include an antibiotic-sensitive skin lesion (acrodermatitis chronica atrophicans) and chronic CNS abnormalities, either polyneuropathy or a subtle encephalopathy with mood, memory, and sleep disorders.
EM is usually diagnosed clinically because it develops before serologic tests become positive.
Cultures of blood and relevant body fluids (eg, CSF, joint fluid) may be obtained, primarily to diagnose other pathogens. Acute (IgM) and convalescent (IgG) antibody titers 2 wk apart may be helpful; positive enzyme-linked immunosorbent assay (C6 ELISA) titers should be confirmed by Western blot. However, seroconversion may be late (eg, > 4 wk) or occasionally absent (eg, if patients received prior antibiotic therapy), and positive IgG titers alone represent previous exposure. If only IgM bands are detected on Western blot, especially long after exposure, the results are often false positive. PCR testing of CSF or synovial fluid is often positive when those sites are involved. Consequently, diagnosis depends on both test results and the presence of typical findings. A classic EM rash strongly suggests Lyme disease, particularly when supported by other elements (eg, recent tick bite, exposure to endemic area, typical systemic symptoms).
In the absence of rash, diagnosis is more difficult. Early-disseminated disease may mimic idiopathic RA in children and reactive arthritis and atypical RA in adults. Important negative RA findings in adults include usually absent morning stiffness, subcutaneous nodules, iridocyclitis, mucosal lesions, rheumatoid factor, and antinuclear antibodies.
In the US, human granulocytic anaplasmosis and babesiosis are also transmitted by I. scapularis and have a common geographic distribution in the northeastern and upper Midwest. Patients ill with any one of the diseases transmitted by I. scapularis may be concurrently infected with the other diseases it transmits. A clinician should suspect that patients with Lyme disease also have babesiosis if they have hemolytic anemia and thrombocytopenia or that they also have human granulocytic anaplasmosis if they have hepatitis, leukopenia, or thrombocytopenia.
Human monocytotropic ehrlichiosis, which is caused by Ehrlichia chaffeensis and transmitted by the Lone Star tick, Amblyomma americanum, occurs mainly in the southeastern and south central US and is unlikely to be confused with Lyme disease. In southern and mid-Atlantic states, bites from the A. americanum tick may result in an EM-like rash accompanied by nonspecific self-limited systemic symptoms and signs. No specific infectious agent has yet been identified as the cause of this disorder (called southern tick-associated rash illness.
Although anaplasmosis, a rickettsial infection, is transmitted by the same tick, clinical coinfection is rare. The lack of leukopenia, thrombocytopenia, elevated aminotransferases, and inclusion bodies in neutrophils helps distinguish Lyme disease from human granulocytic anaplasmosis. Another tick-borne illness, ehrlichiosis (see Ehrlichiosis and Anaplasmosis), which has many similar clinical manifestations, is transmitted by a different tick. Lack of hemolytic anemia (unelevated LDH) and thrombocytopenia helps exclude babesiosis. Acute rheumatic fever is considered in the occasional patient with migratory polyarthralgias and either an increased PR interval or chorea (as a manifestation of meningoencephalitis). However, patients with Lyme disease rarely have heart murmurs or evidence of a preceding streptococcal infection.
Late-stage disease lacks axial involvement, which distinguishes it from spondyloarthropathies with peripheral joint involvement. Lyme disease may cause Bell palsy and, in summer, can manifest with a musculoskeletal aseptic meningitis syndrome that mimics other causes of lymphocytic meningitis or that mimics peripheral neuropathies.
In areas where Lyme disease is endemic, many patients report arthralgias, fatigue, difficulty concentrating, or other nonspecific symptoms. Few patients who have these symptoms but have had no history of EM or other symptoms of early-localized or early-disseminated Lyme disease actually have Lyme disease. In such patients, elevated IgG titers (with normal IgM titers) indicate past exposure, not current or persistent infection, and may, if misinterpreted, lead to long and unnecessary courses of antibiotic therapy. There is no evidence linking B. burgdorferi infection to this fibromyalgia-like or chronic fatigue–like syndrome, often termed chronic Lyme disease.
(See also the Infectious Diseases Society of America's Practice Guidelines for the Treatment of Lyme Disease.) Most features of Lyme disease respond to antibiotics, but treatment of early disease is most successful. In late-stage disease, antibiotics eradicate the bacteria, relieving the arthritis in most people. However, a few genetically predisposed people have persistent arthritis even after the infection has been eliminated because of continued inflammation. Table 1: Guidelines for Antibiotic Treatment Lyme Disease in Adults* shows adult treatment regimens for various presentations of Lyme disease. Treatment in children is similar except that doxycycline is avoided in children < 8 yr and doses are adjusted based on weight (see Table 3: Usual Doses of Commonly Prescribed Antibiotics).
For symptomatic relief, NSAIDs may be used. Complete heart block may require a temporary pacemaker. Tense knee joints due to effusions require aspiration. Some genetically predisposed patients with arthritis of the knee that persists despite antibiotic therapy may respond to arthroscopic synovectomy.
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Precautions against tick bite (see Sidebar 1: Tick Bite Prevention) should be taken by people in endemic areas. Deer tick nymphs, which attack humans, are small and difficult to see. Once attached to the skin, they gorge on blood for days. Transmission of B. burgdorferi does not usually occur until the infected tick has been in place for > 36 h. Thus, searching for ticks after potential exposure and removing them promptly can help prevent infection.
A single dose of doxycycline 200 mg po has been shown to reduce the likelihood of Lyme disease after a deer tick bite. Patients with a known tick bite can easily be instructed to monitor the bite site and seek care if rash or other symptoms occur; the diagnostic dilemma of Lyme is most prominent when there is no history of tick bite.
A vaccine, which had adverse effects similar to symptoms of Lyme disease and was only moderately effective, has been removed from the market.
Last full review/revision March 2014 by Larry M. Bush, MD; Maria T. Perez, MD
Content last modified March 2014