On a warm, summer afternoon an 11-year-old girl presents having had low-grade fevers for 4 days and a rash. On physical examination, the pediatrician notes annular eruptions with erythema on her shoulder and legs (Figure 183-1). The mother states that the rash has gotten progressively larger during the last 3 days and her daughter complains of intermittent joint pain. She does not recall being bitten by an insect. She denies taking medications within the last month and has no known allergies. When asked about recent travel, the mother admits to taking the family on a camping trip in eastern Massachusetts with a return of 5 days ago. The patient was diagnosed with Lyme borreliosis (acute Lyme disease) and started on doxycycline 100 mg twice daily for 14 days. She responded quickly to the antibiotics and never developed the late stage of Lyme disease.

Lyme disease is an infection caused by the spirochete Borrelia burgdorferi, transmitted via tick bite. Most cases of Lyme disease occur in the northeast between April and November. Patients experience flu-like symptoms and may develop the pathognomonic rash, erythema migrans. Lyme disease is prevented by avoiding exposure to the tick vector using insect repellent and protective clothing.

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  In 1977, clusters of patients in Old Lyme, Connecticut, began reporting symptoms originally thought to be juvenile rheumatoid arthritis.¹

  
  
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  In 1981, American entomologist, Dr. Willy Burgdorfer, isolated the infectious pathogen responsible for Lyme disease from the midgut of Ixodes scapularis (a.k.a., black-legged deer ticks; Figure 183-2), which serve as the primary transmission vector in the US.¹

  
  
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  It was identified as a bacterial spirochete and named B. burgdorferi in honor of its founder.

  
  
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  Based on Centers for Disease Control and Prevention (CDC) data reported in 2007, Lyme disease (or Lyme borreliosis) is the most common tickborne illness in the US, with an overall incidence of 7.9 per 100,000 persons.²

  
  
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  In 2010, 94 percent of Lyme disease cases were reported from 12 states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Jersey, New Hampshire, New York, Pennsylvania, Virginia, and Wisconsin.³

  
  
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  Patients living between Maryland and Maine accounted for 93 percent of all reported cases in the US in 2005, with an overall incidence of 31.6 cases for every 100,000 persons.²

  
  
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  The incidence is highest among children 5 to 14 years of age, and more than 90 percent of cases report onset between April and November.²

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  B. burgdorferi begins to multiply in the midgut of I. scapularis ticks upon attaching to humans.

  
  
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  Migration from midgut to salivary glands of ticks requires 24 to 48 hours.

  
  
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  Prior to this migration, host infection rarely occurs.

  
  
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  Common hosts include field mice, white-tailed deer, and household pets.

  
  
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  Ticks must feed on infested hosts in order to infect humans.

  
  
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  Thirty percent of infected patients do not recall being bitten.⁴

  
  
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  Once a human is infected, disease progression is categorized into three clinical stages: early localized, early disseminated, and late disseminated.

Clinical Features

Early Localized (3 to 32 days after tick bite)

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  Erythema migrans (formerly known as erythema chronicum migrans)—This pathognomonic finding occurs in roughly 68 percent of Lyme disease cases.⁴ Described as a “bull’s-eye” eruption (Figures 183-1 and 183-3), this nonpruritic, maculopapular lesion typically occurs near the site of infection. The erythematous perimeter migrates outward over several days while the central area clears. Erythema migrans can persist for 2 to 3 weeks if left untreated.

  
  
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  Flu-like symptoms—Roughly 67 percent of patients will develop flu-like symptoms that can include fever, myalgias, headache, malaise, and lymphadenopathy. Symptoms usually subside within 7 to 10 days.

Early Disseminated (3 to 10 weeks after tick bite)

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  Erythema migrans—Multiple lesions (Figure 183-4).

  
  
  
  
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    May develop as a consequence of bacteremic dissemination to multiple sites.

    
    
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    About 25 percent of children are first diagnosed with Lyme disease based on these lesions.

    
    
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    Lesions are usually smaller than primary lesions and often accompanied by flu-like symptoms.

  
  
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  Cranial nerve palsy—Bell’s palsy (seventh cranial nerve) is the most common neurologic manifestation of Lyme disease, occurring in 3 to 5 percent of children with Lyme disease. However, nearly every cranial nerve has been reported to be involved. Facial nerve palsy is a lower motor neuron lesion that results in weakness of both the lower face and the forehead. Lasting up to 8 weeks, the resolution of symptoms is gradual, begins shortly after initial onset, and does not appear to be influenced by antimicrobial therapy (see Chapter 202, Bell’s Palsy).

  
  
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  Aseptic meningitis—Patients may present with complaints similar to bacterial meningitis (photophobia, nuchal rigidity, and headache), but symptoms are generally less severe in nature. This can also occur with or without concomitant cranial nerve palsy.⁴

  
  
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  Atrioventricular blockade—This is a very uncommon finding in children with Lyme disease. When it does occur, syncope, lightheadedness, and dyspnea are classic symptoms consistent with atrioventricular (AV) dysfunction.³ However, patients can be completely asymptomatic. The degree of Lyme-associated blockade varies so that symptoms are generally episodic. Most cases resolve spontaneously within 1 week.⁴

  
  
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  All of the following can be accompanied by nonspecific signs and symptoms as fatigue, myalgia, headache, fever, and lymphadenopathy.