Lyme Disease
23 related topics
The patient's ECG shows a new heart block and they mention pulling a tick off three weeks ago — connecting those dots fast is the difference between doxycycline and a pacemaker.
Core Concept
Lyme disease is caused by the spirochete Borrelia burgdorferi, transmitted via the bite of an infected Ixodes (black-legged/deer) tick. The tick must be attached for 36–48 hours to transmit the bacterium. The disease progresses through three stages. Early localized (3–30 days post-bite): expanding erythema migrans rash, sometimes with central clearing, appearing at the bite site. This rash is diagnostic; no lab confirmation is needed when present. Flu-like symptoms (fever, fatigue, headache, myalgia) often accompany it. Early disseminated (weeks to months): multiple erythema migrans lesions, cranial nerve palsy (especially facial nerve/Bell palsy), cardiac involvement (AV block, myocarditis), and migratory joint pain. Late disseminated (months to years): chronic arthritis (large joints, especially the knee), peripheral neuropathy, and encephalopathy. Diagnosis uses two-tier serologic testing: ELISA screening followed by Western blot confirmation. Do not test in the first 1–2 weeks — antibodies have not yet developed. For early localized Lyme disease, doxycycline, amoxicillin, or cefuroxime are recommended options depending on age, pregnancy status, allergies, and clinical scenario. Doxycycline is avoided in pregnancy; amoxicillin is commonly used in pregnancy and often in young children, but short doxycycline courses are no longer treated as absolutely contraindicated solely because of age. IV ceftriaxone is reserved for neurologic or severe cardiac involvement. Nursing priorities: proper tick removal using fine-tipped forceps (grasp close to skin, pull straight upward — do not twist, squeeze, or apply heat/petroleum jelly), prevention teaching (light-colored clothing tucked in, DEET repellent, daily tick checks after outdoor activity), and monitoring for Jarisch-Herxheimer reaction (fever, chills, hypotension within 24 hours of starting antibiotics — a cytokine response to dying spirochetes, not an allergy).
Watch Out For
Do not confuse Lyme erythema migrans with cellulitis — cellulitis is uniformly red, warm, and tender without central clearing, while erythema migrans expands outward and is often painless. Note that erythema migrans may not always show the classic bull's-eye pattern. Students frequently confuse the two-tier testing sequence: ELISA comes first as a screening test, Western blot confirms — never order Western blot alone. A common error is assuming doxycycline is absolutely contraindicated in all young children; current guidelines allow short courses in Lyme disease across age groups. Remember that a negative Lyme test in the first two weeks does not rule out infection — seroconversion takes time.
Clinical Pearl
Expanding erythema migrans rash means Lyme — treat now, test later. The rash IS the diagnosis.
Test Your Knowledge
3 quick questions — see how well you understood Lyme Disease