Microbiology · Year 2 · from Microbiology
Case 3: Lyme Disease with Cardiac Manifestations
Presentation
A 28-year-old man from Connecticut presents with fatigue, intermittent palpitations, and near-syncope for the past week. He recalls an outdoor camping trip 3 weeks ago and noticed an expanding red rash on his thigh shortly thereafter that has since faded. He did not see a tick. Physical examination is notable for bradycardia with heart rate of 38 bpm. ECG shows complete heart block (third-degree AV block) with a ventricular escape rhythm. He is hemodynamically stable but is admitted for temporary pacing.
Clinical Image
Erythema migrans - the classic expanding erythematous patch with central clearing ("bull's eye" pattern), the pathognomonic rash of early Lyme disease.
Image Source: Lecture image - Borrelia burgdorferi infection
Questions
- What is the most likely diagnosis, and what organism causes this disease?
- What stage of infection does this patient's cardiac manifestation represent?
- How is the diagnosis confirmed, and what are the limitations of serologic testing?
- What is the treatment approach for Lyme carditis?
Answers
- Diagnosis and organism: This is Lyme carditis caused by Borrelia burgdorferi, a spirochete transmitted by Ixodes (deer) ticks. The history of an expanding "bull's eye" rash (erythema migrans), outdoor exposure in an endemic area (Connecticut, where Lyme disease was first described), and the development of heart block are classic for Lyme disease. Lyme carditis occurs in 1-5% of untreated Lyme disease cases.
- Stage of infection: This represents early disseminated Lyme disease, occurring days to weeks after the initial infection. During this stage, spirochetes disseminate hematogenously from the initial skin inoculation site to various organs including the heart, nervous system, and joints. Cardiac manifestations typically include varying degrees of AV block, with complete heart block being the most severe. The conduction abnormality usually fluctuates and is often reversible with treatment.
- Diagnosis and serologic limitations: Diagnosis is based on clinical presentation combined with two-tier serologic testing (screening with ELISA or IFA, followed by Western blot confirmation). However, serologic tests have limitations: they may be negative early in infection before antibodies develop (the "window period"), they remain positive for months to years after successful treatment, and they cannot distinguish active from past infection. In patients with erythema migrans, treatment should not be delayed for serologic confirmation.
- Treatment for Lyme carditis: Patients with Lyme carditis and high-degree AV block (second-degree type II or third-degree) typically receive intravenous ceftriaxone initially due to concerns about absorption with oral medications and the need for close monitoring. Once the heart block improves, patients can transition to oral therapy (doxycycline or amoxicillin) to complete a 14-21 day course. Temporary pacing may be needed but is usually not permanent, as conduction abnormalities typically resolve within days to weeks of antibiotic treatment. Most patients do not require a permanent pacemaker.