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INITIAL SYMPTOMS:
Erythema migrans (EM) is estimated to occur in 80% of infected patients within 30 days of exposure. "EM is a red, expanding rash, with or without central clearing." EM is often accompanied by flu-like symptoms. [CDC Travel, p. 235]
FINDINGS:
A red macule or papule (erythema migrans) is the initial finding in 70-80% of patients. In the classic presentation, the macule or papule expands concentrically with central clearing (annular shape), reaching a diameter of at least 5 cm. Other symptoms are fever, fatigue, headache, stiff neck, myalgia, arthralgia, and lymphadenopathy. Lyme disease does not develop in experimental animals unless the tick has been attached for 36 hours or longer (May be shorter for Ixodes ricinus;). Weeks to months after onset of erythema migrans, about 5% of patients develop arthritis, 3% have neurological complications, and less than 1% develop cardiac manifestations. [CCDM, p. 363-4] Most patients do not recall a tick bite because the nymph stage of the deer tick is so small. Other stage 2 findings include hematuria, malar rash, urticaria, conjunctivitis, hepatitis, pharyngitis, cough, and splenomegaly. Other possible findings (occurred in a few cases) are orchitis, iritis, choroiditis, myelitis, and osteomyelitis. In children, optic nerve damage may lead to blindness. [PPID, p. 2728-30] Lyme meningitis is preceded by erythema migrans (by 2-10 weeks) in less than 1/2 of cases. Most prominent are symptoms of headache and stiff neck. Other symptoms are fever, fatigue, aches, and weight loss. [PPID, p. 1118] The three stages are: 1.) Early localized (erythema migrans); 2.) Early disseminated (flu-like symptoms that may last for weeks followed by meningitis, Bell's palsy, or heart block); and 3.) Late (arthritis occurring in about 60% of patients usually within several months of erythema migrans); Less common findings are nausea/vomiting, pharyngitis, lymphadenopathy, and splenomegaly. [Merck Manual, p. 1269] EM varies in appearance; it is vesicular-pustular in about 5% of cases, and it may be purpuric on the lower legs. Patients may have tender regional lymphadenopathy. About 20% of patients in the US have more than one EM at the time of diagnosis. Multiple EMs are thought to be caused by hematogenous dissemination of the spirochetes. About 60% of patients not treated with antibiotics will develop arthritis about 6 months after EM with a range of 4 days to 2 years. Tick-bite hypersensitivity reactions occur within 48 hours of the bite, are often pruritic, and do not last as long as EM. EM lasts about 4 weeks. Unlike EM, erythema multiforme often involves mucous membranes, palms, and soles. [Cecil, p. 1930-5]
EPIDEMIOLOGY:
The enzootic transmission cycle is maintained by ixodid ticks and wild rodents. [CCDM] A vaccine became available in 1999, but it was withdrawn by the only manufacturer in 2002. [PPID, p. 2735] Deer play an important role in feeding and transporting ticks, but they are not competent hosts for the spirochetes. [Cecil, p. 1930]
LABORATORY TESTING:
Testing not indicated for patients with subjective symptoms only, e.g., fatigue and muscle pain; High rate of false positives (up to 90%) for IgM Western blot when screening patients with symptoms >1 month; [ABX Guide] CDC criteria: IgM western blot must show at least 2 of 3 defined bands and IgG western blot must show at least 5 of 10 bands to be considered positive. [Harrison, p. 665] Clinical diagnosis (EM and travel to endemic area) is sufficient. Perform 2-tiered serological testing (ELISA/IFA and confirmatory Western blot) for cases of possible disseminated infection. Test with C6-based ELISA if Lyme infection acquired in Europe. [CDC Travel, p. 232]
RELATED INFECTIONS:
Several different strains of B. burgdorferi have been identified in Europe. Southern tick-associated rash illness (STARI) is a related infectious disease that has not yet been completely defined. It resembles Lyme disease with the typical erythema migrans type of rash. However, STARI follows the bite of the lone star tick (Amblyomma americanum) while Lyme disease follows the bite of the black-legged tick (Ixodes scapularis or Ixodes pacificis). The spirochete, Borrelia burgdorferi, causes Lyme disease. Tests for Borrelia burgdorferi are negative in patients with STARI. A spirochete (Borrelia lonestari) has been isolated from a skin biopsy and infected ticks. Treatment is with doxycycline or amoxicillin, and there are no late manifestations. [PPID, p. 3269-70] See http://www.cdc.gov/stari/.
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